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Title: Efficient Electrical Systems Design
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Efﬁcient Electrical Systems
Design Handbook

“This page left intentionally blank
...
E
...
E
...
and
Harry Franz, P
...

Library of Congress Cataloging-in-Publication Data
Thumann, Albert
...

p
...

Includes bibliographical references and index
...
paper) -- ISBN-10: 0-88173-594-9 (electronic)
ISBN-13: 978-1-4398-0300-4 (Taylor & Francis : alk
...
Commercial buildings--Electric equipment
...
Electric power systems
...
Franz, Harry, 1947- II
...

TK4001
...
3--dc22

2008039662

Effcient electrical systems design handbook / by Albert Thumann and Harry Franz
...
All rights reserved
...

Published by The Fairmont Press, Inc
...
fairmontpress
...

6000 Broken Sound Parkway NW, Suite 300
Boca Raton, FL 33487, USA
E-mail: orders@crcpress
...

23-25 Blades Court
Deodar Road
London SW15 2NU, UK
E-mail: uk
...
co
...
)
13: 978-1-4398-0300-4 (Taylor & Francis Ltd
...

iv

This book is dedicated to my father
who showed me how to install
electrical systems
...
”

Contents
Chapter
Page
1 Electrical Basics
...
19
3 Equipment Selection Considerations
...
63
5 Conduit and Conductor Sizing
...
167
7 Using Logic to Simplify Control Systems
...
223
9 Protective Relaying for Power Distribution Systems
...
265
11 Energy Management Systems
...
301
13 Variable Speed Drives
...
337
15 Testing Rewinds to Avoid Motor Efﬁciency Degradation
...
365
References
...
387

vii

“This page left intentionally blank
...
With the advent of high energy costs, plant
and project engineers have needed to become more aware of electrical
systems
...

ix

“This page left intentionally blank
...
Often
included under the general title of electrical engineer are the ﬁelds of electronics, semiconductors, computer science, power, lighting and electromagnetics
...

The following chapter provides a brief review of basic concepts that
serve as background for the electrical engineer
...

ELECTRICAL UNITS
Table 1-1 and the following text provide deﬁnitions of the basic electrical quantities
...
Electrical Quantities in MKS Units

————————————————————————————————
Quantity

Symbol

Deﬁnition

Unit

————————————————————————————————
Force
Energy

f
w

push or pull
ability to do work

Power
Charge
Current
Voltage
Electric ﬁeld
strength
Magnetic ﬂux
density
Magnetic ﬂux

p
q
i
v
E

energy /unit of time
integral of current
rate of ﬂow of charge
energy /unit charge
force/unit charge

B

force/unit charge
momentum
integral of magnetic
weber ﬂux density

φ

Newton
joule or wattsecond
watt
coulomb
ampere
volt
volt/meter
tesla
weber

————————————————————————————————
1

2

Efﬁcient Electrical Systems Design Handbook

“Force”—A force of 1 newton is required to cause a mass of 1 kilogram to
change its velocity at a rate of 1 meter per second
...
The joule or watt-second is the energy
associated with an electromotive force of 1 volt and the passage of
one coulomb of electricity
...
The transformation of 1 joule of energy in 1 second represents an average power of 1 watt
...
The coulomb is deﬁned as
the charge on 6
...

“Current”—The current through an area is deﬁned by the electric charge
passing through per unit of time
...
In a current of 1 ampere, charge is being transferred
at the rate of 1 coulomb per second
...
A charge of 1 coulomb receives or delivers an energy
of 1 joule in moving through a voltage of 1 volt
...
” The electric ﬁeld strength is deﬁned by the
magnitude and direction of the force on a unit positive charge in the
ﬁeld (i
...
, force/unit charge)
...
” The intensity of the
magnetic effect is determined by the magnetic ﬂux density, which
is deﬁned by the magnitude and direction of a force exerted on a
charge moving in the ﬁeld with a certain velocity
...

“Magnetic Flux”—Magnetic ﬂux quantity, in webers, is obtained by integrating magnetic ﬂux density over an area
...
(See the schematic representation in Figure 1-1
...
The
constant that relates the voltage and current is called “resistance
...

Since voltage is the energy per unit charge and current is the charge
per unit time, the basic expression for electrical energy per unit time, or
power, is:
FORMULA 1-2

P = vi = i2R

Consequently, resistance is also deﬁned as a measure of the ability of a
device to dissipate power (in the form of heat)
...
Ohm’s Law Representation

CAPACITANCE
Now let’s connect the battery to two ﬂat plates separated by a small
air space between them
...
)
When a voltage is applied, it is observed that a positive charge appears on
the plate connected to the positive terminal of the battery, and a negative
charge appears on the plate connected to the negative terminal
...
Such a device that stores charge
is called a capacitor
...
The relationship can be expressed by the equation:
FORMULA 1-3

i = C dv/dt

where C is a constant called “capacitance” (measured in farads) and dv/
dt is differential notation representing the rate of change of voltage
...
Capacitance Law

INDUCTANCE
If the signal generator is placed in a circuit in which a coil of wire
is present, it is observed that only a small voltage is required to maintain
a steady current
...
) However, to produce a rapidly changing current, a relatively large voltage is
required
...

Additionally, when a direct current is removed from an inductor
the resulting magnetic ﬁeld collapses, thereby “inducing” a current in an
attempt to maintain the current ﬂow
...

Electrical Basics

5

Figure 1-3
...

These circuit laws allow voltages and currents to be calculated if only some
of the circuit information is known
...
” Kirchoff’s Current Law states
that the sum of the currents ﬂowing into a common point (or node) at any
instant is equal to the sum of the currents ﬂowing out
...
If the circuit represented by Figure 1-4 is analyzed, Kirchoff’s
Law would be utilized as follows:
Kirchoff’s Voltage Law states that the summation of the voltages
measured across all of the components around a loop equals zero
...
Kirchoff’s Current Law

Efﬁcient Electrical Systems Design Handbook

6

one arbitrary direction
...

If the potential decreases, the voltage is said to be negative
...
Kirchoff’s Voltage Law

ALTERNATING CURRENT
Although direct current ﬁnds uses in some semiconductor circuitry,
the primary focus of electrical design is concerned with alternating currents
...
; and alternating patterns (i
...
, sound and light waves)
occur in nature and consequently provide the basis for analysis of signal
transmission
...

FORMULA 1-5

where

a
A
ω
t
α

a = A cos (ωt + α)

= instantaneous value
= amplitude or maximum value
= frequency in radians per second (omega)
= time in seconds
= phase angle in radians (alpha)

Electrical Basics

7

Figure 1-6
...
)
The phase angle α represents the difference between the reference
time t = 0 and the time that the peak amplitude A occurs
...
* In this ﬁgure, the sinusoid is represented as a complex vector rotating with a frequency ω from an initial phase
angle α
...

Using phasor notation for the sinusoid represented by Figure 1-7, we
get:
FORMULA 1-7

a = b + jc = Ac (jα) = A∠α

*For more information on the phasor concept, see Circuits, Devices and Systems, R
...
Smith,
John Wiley and Sons, Inc
...
Phasor Representation of a Sinusoid

Consequently, the term A∠α is a simpliﬁed representation of Formula 1-5 for a given frequency
...

In a circuit with capacitive and inductive elements present, Ohm's
law is modiﬁed to be the following, where all symbols are represented by
phasors:
FORMULA 1-8

Z = V/I

where Z is measured in Ohms
...
We
say that the voltage across an inductive element leads by 90° the current
through it
...
Its reactance is given by:
FORMULA 1-11

where

ZC = VC/IC = 1/ωC∠–90° = 1/2πfC∠–90°,
1
XC = ——
2πfC

Note that the voltage and current are ill phase across a purely resistive
element
...
When inductive and/
or capacitive elements are present, however, the energy is not dissipated
in these elements but is stored and returned to the circuit every half cycle
...

FORMULA 1-12 P = VI COS Θ watts,
where Θ = angle between V and I

The difference between the power in watts and the "volt-amperes" is the
product of a quantity termed the power factor, which is calculated by Formula 1-13
...
This effective value is found to be the “square root of the mean
squared value,” or the root mean square (RMS) value
...
The RMS value is found to be:
FORMULA 1-14

IRMS = IPEAK × 0
...
707

The RMS values are commonly used when referring to distribution
voltages and currents, since this is the value measured by voltmeters and
ammeters
...
Additionally, RMS values of voltage and current are generally used in Formula 1-12, since average power is generally of primary
interest
...
e
...
Express frequency in terms of Hz and assume the phase angle
is zero
...
Since 115 VAC is an RMS value, A
is 115 volts/0
...
From Formula 1-6 ω = 2πf; therefore, for a 60
Hz distribution frequency the expression is:
v = 163 cos (2π60t) volts

THREE-PHASE POWER
Most power is generated and transmitted in three phases in which
three wires are utilized, with the voltage in each equal in magnitude but
differing in phase by 360°/3 = 120° (See Figure 1-8)
...

Generators are more efﬁcient
...

Motors start and run smoother
...

Power is constant rather than ﬂuctuating during the cycle
...
Three-phase Voltages

Phasor addition of the currents and voltages of a three-phase power system yield the following expression for power:
For balanced system
watts = P3φ = √3 (VL–L)(IL) cos Θ watts,
where L = line, L–L = line-to-line

FORMULA 1-15

FORMULA 1-16

watts = P3φ = 3 VφIφ cos Θ,

FORMULA 1-17

VARS = Q3φ = 3 VφIφ sin Θ

FORMULA 1-18

V–A = S3φ = 3 VφIφ

where φ = phase

TRANSFORMERS
Vout
——
Vin

=

Nout
——
Nin

Iin
= ——
Iout

where N = # turns

Figure 1-9
...
This is
accomplished with approximately equal power transfer (i
...
, if the voltage
is increased, the current is decreased a proportionate amount)
...

Transformers contain two separate coils of insulated wire wound on
an iron frame
...

The magnetic ﬁeld in one coil induces current to ﬂow in the other coil by
cutting through the turns of wire
...
Power is generally transferred at very high
distribution voltages (several thousand volts), since the associated current
is relatively low and the distribution losses are much decreased
...
) Additionally, lower
current values allow smaller wires and associated current-carrying equipment to be used
...

DISTRIBUTION VOLTAGES
Modern electrical distribution within facilities has tended toward
higher voltages, for many of the same reasons as utilities have (i
...
, lower
costs associated with lower current carrying needs)
...
(called branch circuit wiring) has tended
to be routed relatively short distances to strategically located transformer
load centers, which are then linked to a central distribution panelboard
...
There are three basic
voltage distribution systems that are used today as described below
...
)
SINGLE-PHASE
This is a commonly used system in residential and small commercial
buildings
...
240 volt branch circuits can be used for power

Electrical Basics

13

Figure 1-10
...
120 volt branch circuits
are used for lighting and receptacles
...
” This system provides three-phase
and single-phase power at a variety of voltages
...

The 120/208 volt conﬁguration is generally available in all except
heavy industrial facilities, to some extent
...

The 277/480 volt system is rapidly becoming the system of choice in
commercial and industrial facilities because of the advantages mentioned
earlier of utilizing higher distribution voltages
...

In a balanced wye system, the magnitude of line currents equal the
phase currents, and the line-to-line voltage is th √3 times the phase voltage
...
Note, however, that the currents from one phase to the other
and not necessarily equal, but due to the neutral wire the line-to-neutral
voltage remains the same even if the load becomes unbalanced
...
Wye Distribution
SIM 1-2

Refer to the second drawing in Figure 1-11
...

Answer

Note (3, 12) rectangular form of the impedance converts to impedance
Z = 12
...
732 = 277 volts
I φ load = 277/12
...
3 amps
I line = I phase = 22
...
f
...
24 → 24% lagging
...

P3φ loads = 3 (277) (22
...
24 = 4
...
3) sin 76 degrees = 18 kVARs
S3φ loads = 3 (277) (22
...
53 kVA
DELTA SYSTEMS
The delta-connected secondary system (Figure 1-12) is available with
phase-to-phase voltages of 240,480 or 600 volts
...
Delta Distribution

motor loads represent a large part of the total load (i
...
, some industrial
facilities)
...

A variation on the delta connection is also shown in Figure 1-12
...
Motors are supplied at 240 volts three-phase, while 120-volt
single-phase circuits are supplied by the neutral conductor and phases B
or C
...

SIM 1-3

Refer to the second drawing in Figure 1-12
...

Answer

Note (3, 12) rectangular form of the impedance converts to impedance
Z = 12
...
4 = 38
...
7 = 67 amps
Power factor = p
...
= cos (76 degrees) = 0
...

Note that the power factor lags due to positive reactive ohms
load
...
7) 0
...
37 kW
Q3φ loads = 3 (480) (38
...
7) = 55
...

These instruments are described below
...
For most audits, alternating currents are measured
...
Ammeters must have relatively low resistance, and are put in series or
clamped around
...
This range can
be extended to 4000 amperes continuously for some models with an accessory step-down current transformer
...
After attachment, the recording ammeter can keep recording
current variations for as long as a full month on one roll of recording paper
...

The ammeter supplies a direct measurement of electrical current,

Electrical Basics

17

which is one of the parameters needed to calculate electrical energy
...

A voltmeter measures the difference in electrical potential between
two points in an electrical circuit
...

In series with the probes are the galvanometer and a ﬁxed resistance (which determine the voltage scale)
...

The voltage drops measured in many instances are fairly constant
and need only be performed once
...

Most voltages measured in practice are under 600 volts; there are
many portable voltmeter/ammeter clamp-ons available for this and
lower ranges
...

Wattmeter and Power Factor Meter
The portable wattmeter can be used to indicate by direct reading
the electrical energy in watts
...

The basic wattmeter consists of three voltage probes and a snap-on
current coil that feeds the wattmeter movement
...
It can be used on both one- and three-phase circuits
...
One of its three voltage probes is attached to each conductor phase
and a snap-on jaw is placed about one of the phases
...

It can measure power factor over a range of 1
...
0 lagging, with ampacities up to 1500 amperes at 600 volts
...

The power factor is a basic parameter whose value must be known
to calculate electric energy usage
...

18

Efﬁcient Electrical Systems Design Handbook

Portable digital kWh and kW demand units are also now available
...
Instantaneous usage, accumulated
usage, projected usage for a particular billing period, alarms when overtarget levels are desired for usage, and control-outputs for load-shedding and cycling are possible
...

Chapter 2

Using the Language of the
Electrical Engineer
To design the electrical portions of an industrial plant or a commercial building requires knowledge of power, lighting, and control
...
This “role playing” experience will enable the reader to gain a
better understanding of the elements that go into the design, to deal better
with contractors and in-house designers, and to interpret the design of an
existing facility
...

•

Technical Proﬁciency
...

•

Cost Considerations
...
Electrical engineering and design manpower requirements should be established, monitored and controlled
...
Schedules should be made for all engineering and construction activities
...
Monitoring progress, spotting areas of concern,
and implementing corrective action are required to ensure an orderly design
...
Since a facility can contain process, power generation,
and ofﬁce areas, you will gain a broad exposure to electrical problems
...

Typical Problem
The Ajax Company* is building a plant
...
Many
clients know what they want, but they need help in deﬁning what has to
be done
...
The design engineer must consider, for example:
•

•
•
•
•
•
•

How to service the loads of the plant
...
)
Type of lighting system required
...

Type of equipment required
...

Economic considerations
...

Engineering Activities
Using the above design criteria, the engineering activities include:
•
•

Establishing criteria for One Line Diagram
...

*The Ajax Company is ﬁctitious, but the principles you will experience are not
...

Inspecting equipment
...

Checking vendor CAD work
...

Preparing estimates
...
Typical diagrams required for
the project are as follows:
•

One-line or Single-line Diagram
This diagram (Figure 2-1) is a basic schematic which identiﬁes how
power is distributed from the source to the user
...
Several one-line diagrams are
often needed
...

•

Motor Control Center (MCC) One-line or Single-line Diagram
A main one-line diagram illustrates the distribution of power by
the MCC to motors and other loads
...
This is to scale and locates equipment in a manner that
is similar to that of a map
...
It is to
scale and shows the actual locations of the electrical power users
...

22

Efﬁcient Electrical Systems Design Handbook

If the project is large, separate diagrams are often used to list the
conduit and cable sizes
...

•

Lighting Plans
A typical lighting plan (Figure 2-5) illustrates by a top view the
physical location of all lighting ﬁxtures and other electrical lighting loads
...
Conduits and cables for lighting are
also physically shown on the lighting plan
...
It is important to note that 120
VAC/240 VAC single-phase receptacles are typically included on
the lighting plans rather than the power plans
...
This
is drawn to scale and shows the actual locations of the instruments
...
If the project is large, separate diagrams are
often used to list more information about instruments and the respective conduit and cable sizes
...
It is important to note that instrument diagrams are not
combined with other diagrams on any job, even if the job is very
small
...
It is to scale
and shows the actual locations of the grounding system, which includes the main grounding loop, grounding branch loops, and location of grounding connections
...
It is important to note that location of
the lightning rods and rod cable downcomers are often shown as
part of the grounding plans
...
Once again, it
is important to note that instrument plans are not combined with
other plans
...

•

Power Panel Board Schedules
A power panel board schedule lists the number, location, and power consumed by the loads on each branch circuit and the receptacles for three-phase loads
...

•

Lighting Panel Board Schedules
A lighting panel board schedule (Figure 2-6) lists the number, location, and power consumed by the lights on each branch circuit
and the receptacles for single-phase 120 V AC and 240 VAC power
loads
...

•

Instrument Panel Board Schedules
An instrument panel board schedule lists the number, location, and
power consumed by the instruments on each branch circuit and
related instrument power loads
...

•

Elevations
A typical elevation illustrates by a front view, usually for layout,
or side view, typically for clariﬁcation of details that are used to
supplement a plan view
...
The electrical NEMA size and physical space size are shown on the MCC layout
...

•

Motor Control Center (MCC) Rear View Elevation
This shows the actual physical location of motor control center buss
horizontal and vertical, electrical buss bars, and the incoming cable
for the motor control center
...

•

Lightning Rod Detail Elevation
This shows the actual mounting of the lightning rods, the rod
downcomer cables to ground, and the connections to the lightning
rods
...

•

Elementary Diagrams
The elementary is a type of schematic
...
The elementary
may be in ladder logic form, as shown in the ﬁgure
...
Note that the elementary diagram indicates how the
system operates but not the physical attributes of each element
...
Terminal numbers and point-to-point connections are shown in their relative location on the interconnection
diagram for each device
...
It is important to note that the
interconnection diagram shows connections from one device to another, as well as the details of connections at each device
...
Terminals number and point-to-point are shown in their
relative location on the connection diagram for single device
...
It is important to note that a connection diagram shows
only connections to a device
...
The details may indicate more information about a special item, more precise item locations, a larger or different view of an item, or any further clariﬁcations necessary
...
It
shows which items are dependent on the completion of other items
and which items are independent from the completion of other
items
...
The previous items in series must be done before the next
item in series
...

DESIGN ACTIVITY HOURS
When dealing with outside contractors and evaluating the scope of
a project, it is useful to have an understanding of how work time estimates are made
...
The
hours for each item depend on the amount of detail shown and the type
of ﬁrm making the design
...
A designer in an engineering ﬁrm would probably show in
addition the circuits to each ﬁxture and a lighting panelboard schedule
...
This table should
serve only as a hypothetical example
...

26

Efﬁcient Electrical Systems Design Handbook

Figure 2-1
...
Typical Power Plan

27

28

Efﬁcient Electrical Systems Design Handbook

Figure 2-3
...
Typical Interconnection Diagram
Table 2-1
...

30

Efﬁcient Electrical Systems Design Handbook

Figure 2-5
...
Typical Lighting Panel

In the following pages you will experience job situations
...
The answer will be written below the problem
...

SIM 2-1

Estimate the number of power and lighting layouts for the following
details
...

Since standard size is 30" × 42", half of the operating and basement
ﬂoor can ﬁt on one layout
...

Lighting Plan—1/8”=1’
50
—
8

×

200
—
8

= 6” × 25"

One layout will be sufﬁcient (30" × 42")
...

Given: 28 motors on two motor control centers with an estimated
load of 800 kVA
...

Answer

Based on the above load, one unit substation and the associated motor control centers will ﬁt on one diagram
...
3

Estimate the number of elementary and interconnection diagrams for
SIM 2-2
...
Control
schemes should be provided so that 14 solenoid valves can be activated
...
, are located on a local panel
...
Allow 2 spaces between each scheme
...

Usually at the beginning of the project it is difﬁcult to get an exact description of the control
...
Assume 2 spaces between each motor
...

Using the Language of the Electrical Engineer

33

In estimating the interconnection diagrams, assume an interconnection diagram is needed for each motor control center and local panel
...

Compile a list with estimated hours for problems SIM 2-1 through

Answer

————————————————————————————————
DESCRIPTION

ESTIMATED HOURS

————————————————————————————————
One Line Diagram
Power Plan
Power Plan
Lighting Diagram—Basement Operating
Grounding Drawing
Conduit and Cable Schedule—Assume 2*
Lighting Schedule—Assume 2
Elementary Diagram
Elementary Diagram
Interconnection MCC No
...
2
Interconnection Local Devices
TOTAL HOURS

75
50
50
30
30
20
20
75
75
30
30
30
515

————————————————————————————————
*One for basement and one for operating ﬂoor
...

From the details of the design, an estimate can be made of the number of requisitions which are needed to purchase equipment
...

•

To write a completely new speciﬁcation may take 60 hours
...
The hours required depend on the
complexity of the equipment being purchased
...
Coordination and general engineering activities may be
from 10-20% for small projects below 5000 hours and 15-30% for larger
ones that need more coordination
...

SIM 2-5

Estimate the engineering hours for the design of 500 hours as indicated in SIM 2-4
...

Answer

Substation Speciﬁcation
Requisition and Vendor Items
Motor Control Centers (2)
Speciﬁcations
Requisition and Vendor Items
Coordination—10% (500)

10
40
10
40
50
150 hours

Notice that the engineering activities on an industrial project are
usually only a fraction of the total time required for design
...
The two organizations widely encountered are:
•
Department Oriented
...
The department head usually has people grouped
together
...

Using the Language of the Electrical Engineer

•

35

Task Force
...

These people move out of the department and operate as a team
...

In the project or task force approach, a project engineer is
assigned to the job to help coordinate the various disciplines
...

Good relations with manufacturers can aid in electrical design
...

•
Technical brochures
...

•
Proven expertise in their ﬁeld
...
Remember, vendors are offering these
services as a means of selling their product
...

ELECTRICAL SCHEDULE
Always Last
Electrical design cannot proceed without the motor horsepowers
...
The electrical engineer is vulnerable to
any changes from the other departments, since such changes will probably affect the electric load
...
This
input is required to design the power and lighting
...
Thus the electrical design is usually the last to
be ﬁnished on a project
...

36

Efﬁcient Electrical Systems Design Handbook

Critical Path
In many cases it is the electrical group which determines the critical
path
...
Thus, one of
the ﬁrst activities the electrical engineer should do is purchase equipment
...

A typical critical path schedule is illustrated in Figure 2-7
...
In these problems you will play the role of an electrical en-

Figure 2-7
...
The plant is comprised of two identical modules
...

The ﬁrst task will be to identify the electrical loads from an equipment list which has been given to the engineer by the plant
...

For example:
A—Architectural
M—Mechanical
H—Heating and Ventilating
Equipment List—Module #1
Note: Module #2 is identical
...

The area of the Process Plant 2 is as follows:
Basement
20 ft × 400 ft
Operating Floor 20 ft × 400 ft
From the above information prepare a list and submit the cost to do
this project
...

Analysis
Once it is known what equipment requires a motor, it is necessary to
obtain the electrical loads from each discipline and compile a motor information ﬁle
...

NO
...
speed

Reversing
Local starter
by vendor
Local starter
by vendor

M
M
M
M

M
M
H
H
H
M
M
M
M
A

————————————————————————————————
Next, prepare an information ﬁle to estimate the hours required to
produce the diagrams and speciﬁcations
...
1 and Local Device
Interconnection MCC No
...
Also it was
assumed that the job is complex
...

“This page left intentionally blank
...

This chapter introduces some of the equipment that the engineer must
size and specify when designing a safe and efﬁcient power distribution
system
...

ELECTRICAL EQUIPMENT
Electrical equipment commonly speciﬁed is as follows:
•
Switchgear Breakers—used to distribute power and provide
overcurrent protection for high voltage applications
...
Consists of a high
voltage disconnect switch, transformer, and low-voltage breakers
...

•

Motor Control/Center (MCC)—a structure which houses starters
and circuit breakers, or fuses for motor control, and various other
control devices
...

(4) AC drive units, which control AC motor speed
...

41

42

Efﬁcient Electrical Systems Design Handbook

(6) Smart overload relays, which protect equipment from high
currents
...

(8) PLC I/O chassis, for programmable logic controlleers
...

•

Panelboard/Switchboard Breakers—used to distribute power and
provide overcurrent protection to motor control centers, lighting,
receptacles, and miscellaneous power circuitry within a building
...
Switchgear breakers may be of the “vacuum type,” whereas
substation breakers may be of the “magnetic air circuit type,” and motor
control center and panelboard breakers may be of the “molded case” type
...
When a short circuit occurs,
many thousand amperes of peak (or asymmetrical) current can ﬂow which
can “fuse” the contacts of a circuit breaker closed, thereby preventing it
from operating to prevent ﬁres, explosions, etc
...
Typical low-voltage breakers (less than 600
volts) breakers are illustrated in Figure 3-1
...

The ﬁrst, or “thermal,” protection is adjusted to prevent the wiring
from overheating when overloaded for a period of time
...

Table 3-1 summarizes breaker and starter sizes for motor control
centers
...
The fuse and breaker sizes indicated in these tables are
based on vendor’s data
...

Equipment Selection Considerations

Table 3-1
...
The instantaneous response occurs
when the solenoid activates the plunger to break the current
path
...
Higher fault interruption
promotes poor current limiting
...

Fuse Circuit
Breakers
and Limiters

These breakers combine the convenience of breakers with
high fault current-limiting characteristics of fuses
...
This is
accomplished by a reverse current loop, which creates a
magnetic force causing the conductors to repel
...

Motor Circuit
Protectors

These breakers are standard types without thermal
element and must be used with overload relays
...
Features include
easy adjustments to ampere rating, long time delay
band, short time delay pickup, short time delay band,
instantaneous pickup, ground fault pickup and ground
fault time delay
...

————————————————————————————————

————————————————————————————————
Figure 3-1
...
Each type is
characterized by its time to isolate the fault, interrupting rating, and
current limiting property
...
Typical fuses
are illustrated in Figure 3-2
...
Full-load Current in Amperes, Direct-current Motors
The following values of full-load currents* are for motors running at base speed
...
0
5
...
8
9
...
2
—
—
—
—
—

3
...
1
5
...
6
9
...
2
17
25
40
58

2
...
6
3
...
8
6
...
3
10
...
6
2
...
7
3
...
7
6
...
5
12
...
6

—
—
—
—
—
—
—
—
—
12
...

Reprinted with permission from NFPA 70-2008, National Electrical Code®, Copyright© 2007, National Fire Protection Association, Quincy,
Massachusetts 02269
...

National Electrical Code® and NEC® are Registered Trademarks of the National Fire Protection Association, Inc
...

Advantages of Fuses Over Breakers
The advantages of fuses over breakers are:
•
Higher interrupting ratings (200,000 amps dual-element fuses)
•
Current limiting action )will limit the short circuit current downstream
of fuse)
•
Lower cost
•
Less affected by corrosive atmosphere
•
Less affected by moisture
•
Less affected by dust
•
Faster clearing

Efﬁcient Electrical Systems Design Handbook

46

Table 3-2b
...
The voltages listed are rated motor
voltages
...

————————————————————————————————
Horsepower

115
Volts

200
Volts

208
Volts

230
Volts

1/6
1/4
1/3
1/2
3/4
1
1-1/2
2
3
5
7-1/2
10

4
...
8
7
...
8
13
...
5
3
...
1
5
...
9
9
...
5
13
...
6
32
...
0
57
...
4
3
...
0
5
...
6
8
...
0
13
...
7
30
...
0
55
...
2
2
...
6
4
...
9
8
...
This reprinted material is not the complete and ofﬁcial position of the N2FPA on the referenced subject, which is represented
only by the standard in its entirety
...
, Quincy, MA
...

•
Adjustable characteristics
SIM 3-1

Indicate the starter size for 10,30 and 100 HP motors
...
Indicate the frame (continuous rating) and trip
(current at which breaker will open) sizes for 7-1/2, 30, 60 and 100 HP
motors
...
Full-load Current, Two-phase Alternating-current Motors (4-Wire)
The following values of full-load current are for motors running at usual speeds
for belted motors and motors with normal torque characteristics
...
41 times the value given
...
The currents listed shall be permitted
for system voltage ranges of 110 to 120, 220 to 240, 440 to 480, and 550 to 600 volts
...
0
4
...
4
9
...
8
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—

20
2
...
2
4
...
9
8
...
2
19
24
36
47
59
69
90
113
133
166
218
270
312
416

1
...
2
1
...
3
3
...
2
6
...
0
12
18
23
29
35
45
56
67
83
109
135
156
208

0
...
0
1
...
8
2
...
3
5
...
0
10
14
19
24
28
36
45
53
66
87
108
125
167

—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
14
18
23
28
32
43

————————————————————————————————
1/2
3/4
1
1-1/2
2
3
5
7-1/2
10
15
20
25
30
40
50
60
75
100
125
150
200

————————————————————————————————
Reprinted with permission from NFPA 70-2008, National Electrical Code®, Copyright© 2007, National Fire Protection Association, Quincy,

Massachusetts 02269
...

National Electrical Code® and NEC® are Registered Trademarks of the National Fire Protection Association, Inc
...

Answer (from Table 3-1)

Horsepower
7-1/2
30
60
100

SIM 3-3

Trip Size
30
70
125
200

Frame Size
100
100
225
225

The short-circuit current available at a motor control center is 25,000
amperes asymmetrical
...

48

Table 3-2d
...

The voltages listed are rated motor voltages
...

——————————————————————————————————————————————

Synchronous-Type Unity Power
Induction-Type Squirrel Cage and Wound Rotor (Amperes)
Factor* (Amperes)
————————————————————————————————————————————— ————————————————————
Horse230
115
460
460
200
575
575
208
2300
2300
230
power
Volts
Volts
Volts
Volts
Volts
Volts
Volts
Volts
Volts
Volts
Volts

——————————————————————————————————————————————
4
...
4
8
...
0
13
...
5
3
...
8
6
...
8
11
...
5
25
...
4
3
...
6
6
...
5
10
...
7
24
...
2
3
...
0
6
...
6
15
...
1
1
...
1
3
...
4
4
...
6
11

0
...
3
1
...
4
2
...
9
61
9

—
—
—
—
—
—
—
—

—
—
—
—
—
—
—
—

—
—
—
—
—
—
—
—

—
—
—
—
—
—
—
—

10
15
20
25
30
40

—
—
—
—
—
—

32
...
3
62
...
2
92
120

30
...
2
59
...
8
88
114

28
42
54
68
80
104

14
21
27
34
40
52

11
17
22
27
32
41

—
—
—
—
—
—

53
63
83

—
—
—
26
32
41

—
—
—
21
26
33

—
—
—
—
—
—

50
60
75
100
125
150
200

—
—
—
—
—
—
—

150
177
221
285
359
414
552

143
169
211
273
343
396
528

130
154
192
248
312
360
480

65
77
96
124
156
180
240

52
62
77
99
125
144
192

—
16
20
26
31
37
49

104
123
155
202
253
302
400

52
61
78
101
126
151
201

42
49
62
81
101
121
161

—
12
15
20
25
30
40

250
300
350
400
450
500

—
—
—
—
—
—

—
—
—
—
—
—

—
—
—
—
—
—

—
—
—
—
—
—

302
361
414
477
515
590

242
289
336
382
412
472

60
72
83
95
103
118

—
—
—
—
—
—

—
—
—
—
—
—

—
—
—
—
—
—

—
—
—
—
—
—

——————————————————————————————————————————————

——————————————————————————————————————————————

——————————————————————————————————————————————

——————————————————————————————————————————————
*For 90 and 80 percent power factor, the ﬁgures shall be multiplied by 1
...
25, respectively
...
Combination Fuse-switch Ampere Ratings

————————————————————————————————
MOTOR
HP

460 V
FLA

1
1%
2
3
5
7%
10
15
20
25
30

1
...
6
3
...
8
7
...

** Based on MCC vendor’s data for FVNR starters
...

————————————————————————————————

Answer (from Table 3-1)

Horsepower
Trip Size
Frame Size
7-1/2
70
225
Min
...
Either the short-circuit current should be
decreased, or fuses should be used instead of breakers
...

————————————————————————————————

Fast-Acting Fuses These non-time delay fuses are single-element construction
(Non-Time Delay) and have a very high degree of current limitation in the
short circuit region
...

Low Peak DualElement Fuses

Similar to dual-element fuses, these fuses are considerably
more current-limiting in the short circuit region
...

Semiconductor
Fuses

These special fuses have an extremely high degree of current
limitation and are used to protect power superconductors
...
Typical Fuse Types

SIM 3-4

Indicate the fuse and switch sizes for the following: 3, 10,
50, 75 HP motors
...
Dimensions vary
between vendors, and the space allocated for wiring depends on whether
cables enter from top or bottom and whether terminal blocks are required
in upper or lower section
...

Figure 3-3
...
C
...
Outline
(Consult Vendor for Speciﬁc Dimensions)

Referring to Figure 3-3, a vertical section is a structure with an
overall height of 90”, a width of 20” and a depth of nominally 13”-20”
...
A unit is the motor starter-disconnect
module that ﬁts into the vertical section and is covered by a door
...
The working height
is the available space in any section for motor control center units
...

52

Efﬁcient Electrical Systems Design Handbook

•

Place the various required units in as many sections as necessary to
accommodate them
...
Filler plates can be used for
leftover spaces
...
The sizes shown in Figure 3-4 are
based on combination fuse starters
...

Typical symbols used for an MCC one-line diagram are illustrated in
Figure 3-5
...
(Invented by Nicola Tesla to replace the more complicated
and higher maintenance DC motors that have commutators and brushes
...
The speed of the rotor
depends on the frequency into the motor and the number of poles which
come in pairs
...
) = ————————————————
(number of pairs of poles per phase)

(Formula 3-1a)

(Formula 3-1b)

Full-voltage Non-reversing AC Induction Motor (FVNR)
Basically this starts across the line and either runs or stops
...

Equipment Selection Considerations

53

————————————————————————————————
FVNR = FULL VOLTAGE NON-REVERSE
FVR = FULL VOLTAGE REVERSE
TSCP = 2 SPEED SINGLE WINDING
TSSW = 2 SPEED SEPARATE WINDING

————————————————————————————————
(NOTE: ALL SPACE FACTORS 20” WIDE)
FILLER PLATE: 1 SPACE FACTOR (14” HIGH) THRU 5 SPACE FACTORS (70” HIGH)

————————————————————————————————
ONE SPACE FACTOR 14” HIGH:

NEMA SIZE ONE FVNR
NEMA SIZE TWO FVNR
30 AMP FUSED SWITCH
60 AMP FUSED SWITCH

————————————————————————————————
TWO SPACE FACTORS (28” HIGH):

NEMA SIZE THREE FVNR
NEMA SIZE ONE FVR
NEMA SIZE TWO FVR
NEMA SIZE ONE TSCP FVNR
NEMA SIZE THO TSCP FVNR
200 AMP FUSED SWITCH

————————————————————————————————
THREE SPACE FACTORS (42” HIGH):

NEMA SIZE FOUR FVNR
NEMA SIZE THREE FVNR
NEMA SIZE ONE FVNR
NEMA SIZE TWO FVNR
200 AMP FUSED SWITCH

————————————————————————————————
FOUR SPACE FACTORS (56” HIGH):

NEMA SIZE FOUR FVR
NEMA SIZE THREE TSCP FVR
NEMA SIZE THREE TSSW FVNR

————————————————————————————————
FIVE SPACE FACTORS (70” HIGH):

NEMA SIZE FIVE FVNR
NEMA SIZE FIVE FVR
NEMA SIZE FOUR TSCP FVNR
NEMA SIZE FIVE TSCP FVNR
NEMA SIZE FOUR TSCP FVR
NEMA SIZE FIVE TSCP FVR
NEMA SIZE FOUR TSSW FVNR
NEMA SIZE FIVE TSSW FVNR

————————————————————————————————

Note: The minimum bus for a motor control center is 600 amperes
...
This is usually adequate
...

————————————————————————————————
Figure 3-4
...
Symbols for an M
...
C
...
The single-phase motor requires two power leads, and the
three-phase version requires three power leads
...

A single-phase AC induction motor will reverse if its two power leads are
swapped
...
Exchanging just any two of the three
power leads to the three-phase motor will change the phase-sequence

Equipment Selection Considerations

55

and cause reversal
...

Full-voltage Two-speed Consequent Pole AC Induction Motor (TSCP)
This starts across the line and either runs fast or slow, or stops
...
The speed action is accomplished by
the controls using certain power leads to the motor
...
The motor will run the other speed if a lead is
chosen so that only part of the set of poles is used
...

The single-phase motor requires four power leads, and the three-phase
version requires six power leads
...
The three-phase
version that uses six power leads will use either one set of three power
leads for slow, or the other set of three power leads for fast
...

Thus, if the frequency is ﬁxed, the effective number of motor poles
should be changed to change the speed
...
Three-phase two-speed
motors require six power leads
...
The speed of a
DC motor is changed by varying the ﬁeld voltage through a rheostat, or
through higher efﬁciency solid state controls
...

Synchronous Motors are used when constant speed operation
is essential
...

Synchronous motors also are considered for power factor correction
...
8 P
...
synchronous motor will supply corrective kVARs to the system
...
Since
many synchronous motors are self-excited, only the power cables are

Efﬁcient Electrical Systems Design Handbook

56

required to the motor
...

Additionally, these motors offer signiﬁcant improvement in power factor
...

Variable Speed Drives utilizing inverters are being used to change
the frequency of power (and thereby the speed) supplied to standard
induction motors
...
(Note, that a 50% reduction
in speed yields an 88% reduction in power required for a fan
...

In order to relate the motor horsepower to a kilowatt (kW), multiply
the horsepower by
...

kW =

HP ×
...
Efﬁciency vs Horsepower Rating (Dripproof Motors)

Equipment Selection Considerations

57

HP = Motor Horsepower
η = Efﬁciency of Motor
Motor efﬁciencies and power factors vary with load
...
Values are based on totally enclosed fan-cooled
motors (TEFC) running at 1800 RPM “T” frame
...

—————————————————————————
HP RANGE

3-30

40-100

η% at
1/2 Load
3/4 Load
Full Load

83
...
8
86
...
2
90
...
9

P
...
at
1/2 Load
3/4 Load
Full Load

70
...
2
83
...
2
85
...
4

—————————————————————————

—————————————————————————

—————————————————————————

Figure 3-7
...
These
motors are usually fed from a lighting or panel and do not appear on the
MCC one-line diagram
...

Motors 1/2 HP to 250 HP are usually fed from a 480-volt, 3-phase,
motor control center or equivalent
...
The
reason for this is mostly economics, i
...
, price of motor, starter, cable and
transformer
...

Answer

Frequency × 120
60 × 120
No
...
Find the RPM rated speed
...
Find the RPM rated speed
...
Motor HP are: 1/4, 25, 150, and 400
...
16 KV

1φ
3φ
3φ
3φ

—————————————————————————

—————————————————————————
SUMMARY
Circuit breakers and fuses are used to protect wiring and equipment
from fault currents
...

Motor efﬁciency and power factor are dependent on size and load
...

JOB SIMULATION—SUMMARY PROBLEM
SIM 3-7
Background

(a) From the motor list established in SIM 2-6 at the end of Chapter
2, indicate the rated voltage of each motor and if it is a single- or threephase
...
Assume a
30 Amp switch in each MCC to take care of lighting loads and fractional
horsepower motors
...
Assume each module is fed from a separate MCC
...
Typical forms are illustrated
...

DESCRIPTION

HP

VOLTAGE

PHASE

60
100
30
10
25

460
460
460
460
460

3
3
3
3
3

20
40
20
1/6
50
20
5
3/4
1/8

460
460
460
110
460
460
460
460
110

3
3
3
1
3
3
3
3
1

————————————————————————————————
AG-1
CF-3
FP-4
TP-5
CTP-6

CT-9
HF-10
HF-11
UH-12
BC-13
C-16
H-17
SC-19
RD-22

Agitator Motor
Centrifuge Motor
Feed Pump Motor
Transfer Pump Motor
Cooling Tower
Feed Pump Motor
Cooling Tower Motor
H&V Supply Fan Motor
H&V Exhaust Fan Motor
Unit Heater Motor
Brine Compressor Motor
Conveyor Motor
Hoist Motor
Self-Cleaning Strainer Motor
Roll-Up Door Motor

————————————————————————————————
(b) A typical response the client would expect to SIM 3-7 would look
as follows:

Equipment Selection Considerations

61

“This page left intentionally blank
...
This chapter illustrates some of the simple concepts involved in establishing a one-line diagram, determining system reliability, and determining breaker interrupting capacities
...

THE POWER TRIANGLE
The total power requirement of a load is made up of two components, namely the resistive part and the reactive part
...
The pure resistive
power is known as the watt, while the reactive power is referred to as the
reactive volt amperes
...
The closer Θ equals 0° or power
factor approaches unity, the smaller the kVA
...
The
statement usually causes the customer to pay an additional power rate if
the power factor of the plant deviates substantially from unity
...
Similarly, a facility wishes to maximize the efﬁciency
of its distribution equipment by minimizing current levels with a high
power factor
...

The loads of many institutions and industry are usually more inductive loads that include motors and transformers
...
The
equipment must be sized larger to provide the same amount of energy
...

To counterbalance this situation, power factor correcting capacitors
are usually added to correct the power factor close to the ideal value of
100%, usually at about 95%
...

Power factor correction can often be done for an entire site; however,
power factor correction is also often done at various individual locations
and even at individual pieces of equipment
...
This is often done on project expansions to
“free up” the load of equipment, rather than purchase and replace existing
equipment with larger units, transformers, for example
...
Also if it is desired to obtain a power factor that is very close to the 100% ideal power, say 98%, at least some of the
capacitors should have an automatic switching feature
...

Power Factor Correction
The problem facing the electrical engineer is to determine the power
factor of the plant and to install equipment such as capacitor banks or

Efﬁcient Electrical Systems Design Handbook

66

synchronous motors so that the overall power factor will meet the utility
company’s objectives
...

SIM 4-1

A total motor horsepower load of 854 is made up of motors ranging
from 40-100 horsepower
...
Refer to Table 3-3
for efﬁciency and power factor values
...
746
———————————
Motor Eff
...
909 and PF =
...
746
—————

...
87

= 806

SIM 4-2

As an initial approximation for sizing a transformer assume that a
horsepower equals a kVA
...

Answer

Total HP = 854
HP = kVA = 854
Problem answer = 806

For an initial estimate, equating horsepower to kVA is done in industry
...
The load at which the
motor is operating is not established at the beginning of a project, and this
approach usually gives a conservative answer
...
95
...
87
...
87 corresponds to an angle of 29°
...
95 is required
...
95
Θ = 18°
The kVAR of 386 needs to be reduced by adding capacitors
...

Thus, the desired power triangle would look as follows:

CoS Θ =
...
31
701
—— = 738

...

kVARc = 738 Sin 18° = 738 ×
...
Find the (capacitive)
MVARSc added to correct the power factor to 95% lag, which is often the
practical desired value for the power factor
...
8 original power factor = 4 MW original
...

Correcting the power factor does not change the wattage; hence,
the new MW = original MW = 4 MW
...
95, lag so the new MVA = (new MW/0
...
21 MVA new
...
21 MVA
new2 – 4 MW2 new)1/2 = 1
...

The original MVARS – new MVARS gives the added MVARS
...
31 new MVARS = 1
...

SIM 4-5

A plant original load is 200 kVA @ pf = 90% lag; ﬁnd the (capacitive)
kVARSc added to correct the power factor to 100% in-phase, the ideal
power factor
...
9 original power
factor = 180 kW original
...
2
kVARS original
...
Note that its pf = cos
zero = 1
...
Original
87
...
0 new kVARS = 87
...

SIM 4-6

Assume that all motors in SIM 4-1 are not running at the same time
...
1
...

Analyzing Power Distribution Systems
Answer

kVA+
kVAMin
...
1

Many times in industry the transformer capacity is simply based
on the sum of the motor horsepowers plus an additional factor to take
into account growth
...

Remember that electrical loads seldom shrink
...
Additional beneﬁts are derived by capacitor location
...
Maximum beneﬁt of capacitors is derived by locating them as closely as possible to the load
...
This, in turn, will substantially reduce power
losses of the system
...
When power losses are reduced, voltage at the motor increases;
thus, motor performance also increases
...
Note that in all three locations, extra switches are
not required, since the capacitor is either switched with the motor starter
or the breaker before the starter
...
In Case C1B, as in Case C1A, the capacitor is
energized only when the motor is in operation
...
In position C1C, the capacitor is permanently connected to the circuit, but it does not require a separate switch, since it can
be disconnected by the breaker before the starter
...
If this condition
exists, damaging overvoltage or transient torques can occur
...

The next preference for capacitor locations, as illustrated by Figure

Efﬁcient Electrical Systems Design Handbook

70

Figure 4-1
...
In these locations, a breaker or switch will be
required
...
The advantage of
locating capacitors at power centers or feeders is that they can be grouped
together
...

POWER FLOW CONCEPT
Power ﬂowing is analogous to water ﬂowing in a pipe
...
Several branches from the main pipe service various loads
...
Similarly, a large feeder at a high voltage services a plant
...

Analyzing Power Distribution Systems

71

The switchgear breakers serve as a protector for each of the smaller feeders
...

HOW TO CREATE A ONE-LINE DIAGRAM
An overall one-line diagram indicates where loads are located and
how they are fed
...
(Remember that initial design is
based on your best estimate
...

(a) For single buildings and small complexes without heavy equipment loads, incoming voltage levels may be 208 or 480 volts
...
8 kV
...
8 kV
...
8 kV or 33 kV are typical
values
...
(Certain
loads are more economical
...

•

The third step is to establish equipment types, sizes and ratings
...
The type
of process and plant requirements are the deciding factors
...

Efﬁcient Electrical Systems Design Handbook

72

The three commonly used primary distribution systems for industrial plants are simple radial, primary selective, and secondary selective
systems
...
As Figure 4-2 indicates, it is composed of one feed and one transformer
...
See Figure 4-3
...
As Figure 4-4 indicates, it is composed of two complete
substations joined by a tie breaker
...

Simple Radial System

Figure 4-3
...
Secondary Selective System

Analyzing Power Distribution Systems

73

SIM 4-7

Develop the one-line diagram for the Ajax Plant
...

Step 1: Establish loads and their locations
...
1
Process Unit No
...

Answer

See Figure 4-6
...
Ajax Plant Layout

74

Efﬁcient Electrical Systems Design Handbook

Figure 4-6
...

Assume plant capacity may triple in the future and the utility primary
voltage is 115 kV
...
Since
the plant load may triple in the future, 13
...

SIM 4
...
Substations should be
located as closely as possible to the load center
...

Use standard size transformers illustrated in Table 4-1, and size at least
1
...

Analyzing Power Distribution Systems

Administration Building
Feed from same Transformer
Machine Shop
Warehouse
Boiler House
Process Unit No
...
2

75

Load
210
340
185
675
890
765
3065

Total Load

Locate substations and switchgear on Figure 4-5
...

Answer

Administration Building
Feed from same Transformer
Machine Shop
Warehouse
Boiler House
Process Unit No
...
2

Load
1
...
It becomes impractical
to run this size feeder to each substation
...

The substations and switchgear are located on Figure 4-6
...

SIM 4-10

Make a one-line diagram for SIM 4-7
...
Provide two switchgear breakers,
one feeding the process substations and the second feeding the utility and
auxiliary areas
...

76

Efﬁcient Electrical Systems Design Handbook

GENERAL TIPS FOR DISTRIBUTION SYSTEMS
•

Always size unit substations with growth capacity (25% growth capacity for transformers is common practice)
...
A 1000 kVA dry-type
transformer with fans is good for 1333 kVA (33% increase)
...
Overall One-line Diagram

Analyzing Power Distribution Systems

77

oil-type transformer a factor of 25% is used
...

•

The question comes up as to where to locate equipment
...
Substations and motor control centers are usually located indoors in electrical rooms
...

•

Do not allow roof penetrations
...

•

Do not allow other trades to use electrical room space
...
(Special equipment,
such as computers, may require air conditioning
...
Use the recommended clearances established by
the vendor
...

SHORT-CIRCUIT CURRENTS
Faults occur for many reasons: deterioration of insulation, accidents,
rats electrocuted across power leads, equipment failure, and a multitude
of other events
...
At
ﬁrst it has an initial peak or asymmetrical value, but after a period of time
it will become symmetrical about the zero axis
...

Efﬁcient Electrical Systems Design Handbook

78

RATING SUBSTATION BREAKERS (480V)
All breakers should be sized to meet the full-load current and the
available short-circuit current
...
Coordination of protective devices such as breakers means:
(a) That a protective device will not trip under normal operating
conditions, such as when the motor is started
...

The impedance of the transformer limits the amount of short-circuit
current that could ﬂow
...
Use this table as a
guide; a more detailed analysis is required on actual selection
...
75% impedance, and available primary short circuit of 250 MVA, determine the short-circuit current, assuming
100% motor contribution
...

Note: Usually at the beginning of a project, if no utility data are available,
assume unlimited short-circuit current and 100% motor load contribution
...
Select a breaker frame to meet this load
...

From Table 4-1, the 1600 ampere breaker is the minimum breaker

Based on a continuous current rating, a 600 ampere frame breaker
would have been sufﬁcient, but the 600 ampere breaker can only handle
a short-circuit current of 22,000 amperes
...
Thus, the frame size required is 1600 amperes
...
Short-circuit Application Table: 480 Volts, Three-phase

79

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Efﬁcient Electrical Systems Design Handbook

/more/

Analyzing Power Distribution Systems

81

Table 4-1
...
To protect the motor control center, a 600
ampere trip would be chosen
...
To get competitive
bids, requests for quotations are initiated with several bidders
...

•

Check to see if a vendor has met speciﬁcations
...

•

Look at advantages and disadvantages with each vendor
...
may affect the ﬁnal recommendation
...

•

Evaluate cost picture
...

Sometimes a client may wish to direct purchase an item, due to overriding factors, such as spare parts or to match an existing installation
...
Exclude motors below 3 HP from computations
...
The plant is comprised of two identical
modules (two motors for each equipment number listed in SIM 2-6)
...
)

(b)

Based on the total kVA of the plant, determine the transformer size
and the rating of each breaker
...
The substation data will be sent to the three industries
listed below for competitive bids:
Recommended vendors:

(c)

ABC Industries
DEF Industries
GHI Industries

Based on the substation quotes received in SIM 3-7(b), recommend a
vendor
...

Complete the following form:
Simpliﬁed Bid Analysis Form

————————————————————————————————
Vendor’s
Name

Vendor’s
Name

Vendor’s
Name

————————————————————————————————
Cost per
Substation
Delivery
Meets Speciﬁcation
Overall Area

————————————————————————————————
Bidder Recommended
Reason:

Analyzing Power Distribution Systems

(a)

83

Based on the motor list, the plant power factor was estimated at
...

Here’s what the client expected to see:
Module #1
Lighting kW3 = 40 Total

————————————————————————————————
Motors 3-30

Motors 40-100

————————————————————————————————
30

60

10

100

25

40

20

50

20

250

20
5
130

————————————————————————————————
At Full Load:
PF = 83
...
2

PF = 87
...
9

130 ×
...
83 ×
...
746
= ———— = 238

...
87

kW1

kW2

=kVA2 CoSΘ

= kVA CoSΘ
= kVA
...
87

= 112

= 207

kVAR1

= kVA1 SinΘ

kVAR2= kVA2 SinΘ

kVAR1

= kVA1 ×
...
54
= 73

Θ = 29°

kVAR2 = kVA2 ×
...
87
774

(b)

The substation requisition should have included a 1000 kVA transformer and two 600 ampere feeder breakers
...
25 (Total kVA) = 1
...

The closest transformer size is 1000 kVA
...
This
size is required even though the total load on each breaker is 774 ÷ 2 = 387
kVA or
387 k = 466 Amps
3 x 480
The breaker must be sized to meet the short-circuit current of approximately 25,000 amps symmetrical
...
Incoming line compartment with load interrupter switch and current
limiting fuse
2
...
8 kV to 480 volt wye
3
...

Total Price is $37,000
...

Standard terms 30 days from date of invoice
...
See

Analyzing Power Distribution Systems

85

DEF Industries
Gentlemen:
We regret to inform you that at this time we cannot quote
...

Very truly yours,
/s/Dee Frank
GHI Industries
Dear Sir:
We wish to offer our package completely in accordance with your speciﬁcations
...

The above prices are quoted F
...
B
...

The earliest time equipment can be shipped is 40 weeks after receipt of order
...

Yours very truly,
/s/Gee Hi Eye

Efﬁcient Electrical Systems Design Handbook

86

(c)

A completed bid analysis form:

————————————————————————————————
Vendor’s
Name

Vendor’s
Name

Vendor’s
Name

ABC Ind
...

GHI Ind
...

Lower price
...
Since loads constantly change,
a sizing based on the sum of the motor and miscellaneous loads, plus 25%
extra gives a reasonable initial basis for determining capacity
...

The one-line diagram is the single most important drawing for the
electrical design
...
By
use of the one-line diagram, problem areas can be located and corrective
action can be taken
...
Table 5-1 lists a number of insulations commonly used
...
Types THW, RHW,
and XHHW are frequently used in industrial plants for 600 volt or less
distribution
...
Sometimes the designations 0, 00, 000, and 0000 are
referred to as 1/0, 2/0, 3/0, 4/0, respectively
...
Copies of the complete code are available from the association,
Batterymarch Park, Quincy, Massachusetts 02269
...

Answer

From Table 5-2 (page 91) type THW is rated for 310 amperes
...

SIM 5-3

Determine the ampacity for (3) 4/0 cross-linked polyethylene copper
conductors run in conduit at 86°F in a dry location
...
Conductors for Use in Raceways (A Partial Listing)

———————————————————————————————
TYPE

INSULATION

———————————————————————————————
FEP
Fluorinated Ethylene Propylene
MI
Mineral Insulation (metal sheathed)
RH
Heat-resistant Rubber
RHH
High-heat-resistant Rubber
RHW
Moisture and Heat-resistant Rubber
RUH
Heat-resistant Latex Rubber
RUW
Moisture-resistant Latex Rubber
T
Thermoplastic
TW
Moisture-resistant Thermoplastic
THW
Moisture and Heat-resistant Thermoplastic
THWN
Moisture and Heat-resistant Thermoplastic with Nylon Jacket
THHN
High-heat -resistant Thermoplastic with Nylon Jacket
XHHW
Moisture and Heat-resistant Cross-linked Synthetic Polymer
V
Varnished Cambric
UF
Underground Feeder
NOTE: Asbestos (A) is banned from use due to carcinogenic properties
...
When used in a dry location, it is good for 90°C
...

CONDUCTOR DERATINGS
Derating Due to the Number of Conductors
If three conductors or less are run in a conduit, no derating need
be applied
...
For example: 4 to 6 conductors derate the cable
80%; 7 to 24, 70%; 25 to 42, 60%; and 43 and above, 50%
...

Derating Due to Ambient Temperature
If the ambient differs from 30°C, another derating should be applied
...

Conduit and Conductor Sizing

89

SIM 5-4

What is the allowable ampacity of (6) 500 MCM, THW copper
conductors run in the same conduit at 50°C ambient?
Answer

From Table 5-2 (page 91), the allowable ampacity of 500 MCM cable
is 380 amperes
...
8; derating for 50°C is
...

Allowable ampacity =
...
8 ×
...
Doubling the area of a conductor, i
...
, 500 MCM cable to a 1000
MCM cable, does not double the ampacity rating
...
Using conductors larger than 500 MCM
is also not recommended, due to difﬁculties in installation
...

CABLE SIZING
Sizing a Feeder to a Motor for Continuous Service
The minimum size cable for power conductors is #12
...
25 × the full load amperes of the
motor
...

SIM 5-5

What cable size should be used for a 50 HP induction motor? Assume
the cable is type THW and run in conduit
...

Answer

From Table 3-2d (page 48), Chapter 3, a 50 HP motor has an FLA (full
load amperes) of 65 amps
...
25 × 65 = 81
amps
...

Sizing Feeder to Several Motors
The size of the feeder which has more than one motor unit is based
on 1
...
Note: If two or more motors “tie” for the largest,
multiply only the FLA of one by 1
...

90

Table 5-2
...
This reprinted
material is not the complete and ofﬁcial position of the N2FPA on the referenced subject, which is represented only by the standard in its entirety
...
, Quincy, MA
...
(Continued)

91

92

Table 5-2
...
(Continued)

93

94

Table 5-2
...
(Continued)

95

96

Table 5-2
...
(Continued)

97

98

Table 5-2
...
(Continued)

99

100

Table 5-2
...

Determine the size of the feeder if it is rated for ambient 30°C and cable
run in conduit
...
)
Answer

FLA – 30 HP motor – 40 amps (from Table 3-2d)
...

Cable must meet: (1
...

The nearest cable size from Table 5-2 (page 90) is #1 THW
...
Depending
on the application the material used for the conduit can be rigid steel,
electrical metallic tubing (EMT), ﬂexible metal or PVC
...

The size of a conduit depends on the allowable percent ﬁll of the
conduit area
...
Table 5-4 is based on Table
5-3 and enables the engineer to readily select the number of conductors
which can be installed in a conduit
...

Table 1 Percent of Cross Section of Conduit and Tubing for Conductors

———————————————————————————————
Number of Conductors

All Conductor Types

1
2
Over 2

53
31
40

———————————————————————————————
———————————————————————————————

FPN No
...
It should be recognized that,
for certain conditions, a larger size conduit or a lesser conduit ﬁll should be considered
...
2: When pulling three conductors or cables into a raceway, if the ratio of the raceway (inside diameter) to the conductor or cable (outside diameter) is between 2
...
2, jamming can occur
...

Reprinted with permission from NFPA 70-2008, National Electrical Code®, Copyright©2007, National Fire Protection
Association, Quincy, Massachusetts 02269
...

National Electrical Code® and NEC® are Registered Trademarks of the National Fire Protection Association, Inc
...

Efﬁcient Electrical Systems Design Handbook

102

Annex C, from the 2008 National Electric Code®, is duplicated at the
end of this chapter
...

SIM 5-7

What is the allowable percent ﬁll for three conductors (type THW)
run in conduit?
Answer

From Table 5-3, 40%
...
1 to Process Panel No
...
What size conduit is required?
Answer

From Table 5-3 the maximum conduit ﬁll is 40%
...
Since 40 wires can be
run in a 1-1/4” conduit, the correct size is 1-1/4”
...
An example might be a local
STOP-START pushbutton at the motor
...

Above this size, it becomes impractical to pull the smaller control wires
with the larger power conductors
...
Then
look at Table 5-4 under the appropriate percent ﬁll column and choose
a conduit size whose area is equal to or greater than the total conductor
area
...

SIM 5-9

Determine the conduit size for the 50 HP motor, in SIM 5-5
...

Answer

From SIM 5-5, #4 conductors are required for a 50 HP motor
...
Multiply
the area by 3 to get the total area
...

Reprinted with permission from NFPA 70-2008, National Electrical Code®, Copyright©2007, National Fire Protection
Association, Quincy, Massachusetts 02269
...

Efﬁcient Electrical Systems Design Handbook

104

cable sizing
...
1087 =
...
0206 =
...
3879

From Table 5-4, based on 40% ﬁll, conduit size is 1-1/4”
...
Each motor and its associated auxiliaries can
be determined at a glance
...

POWER LAYOUTS
Power layouts are drawn to scale (usually 1/4” = 1’)
...
Usually conduits
run vertically and horizontally
...
Conduit
layouts should be coordinated with other groups (Piping, HVAC) to avoid
interferences
...

Conduit and Conductor Sizing

105

Answer

JOB SIMULATION - SUMMARY PROBLEM
SIM 5-11

(a) With the motor data of 81M 2-6 (Chapter 2) establish a conduit
and cable schedule (ambient 40°C and wire type THW
...
No local
control is provided for the two-speed motor, the reversing motors, and
AG-1 and FP4
...

When power and control are run in the same conduit, designate the
conduit by PC-motor number
...
For
control alone, use C-motor number
...
Use #14 for control
...

Note: Cable size 3 is not frequently used
...

Analysis

(a) See the conduit schedule on the following page
...
25% of the FLA
of the largest motor, plus the full load amps of the others
...
The lighting and fractional HP load of
approximately IS amps is then added, bringing the total to 540 amps
...
88 = 545
...

Efﬁcient Electrical Systems Design Handbook

106

(a)

Conduit Schedule

————————————————————————————————
Conduit No
...

Size

Conduit Size

P-AG1
P-CF3
P-FP4
PC-TP-5

1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1

#2
#2/0
#6
#12
#14
#6
#14
#8
#4
#14
#8
#14
#2
#14
#8
#12
#12
#14

1-1/4”
1-1/2”
1”

————————————————————————————————

PC-CTP6
P-CT9
PC-HF10
PC-HF11
PC-BC13
P-C16
P-H17
PC-SC19

}
}
}
}
}
}

3/4”
1”
3/4”
3/4”
1”
1-1/4”
3/4”
1/2”
3/4”

————————————————————————————————
SUMMARY
The National Electrical Code gives speciﬁc tables for calculating
ampacities and conduit sizes for different cables and various conditions
...
Wireways and trays
are used as a raceway to carry the cable
...

Conduit and Conductor Sizing

107

The following tables are reprinted with permission from the NFPA 70-2008
National Electricl Code®
...
This reprinted material is not the complete and ofﬁcial position of the NFPA on the referenced subject, which is represented only by
the standard in its entirety
...

Annex C

Conduit and Tubing Fill Tables for Conductors and
Fixture Wires of the Same Size

This annex is not a part of the requirements of this NFPA document but is included for
informational purposes only
...
1 — Electrical Metallic Tubing (EMT)
C
...
2 — Electrical Nonmetallic Tubing (ENT)
C
...
3 — Flexible Metal Conduit (FMC)
C
...
4 — Intermediate Metal Conduit (IMC)
C
...
5 — Liquidtight Flexible Nonmetallic Conduit (Type LFNC—B)
C
...
6 — Liquidtight Flexible Nonmetallic Conduit (Type LFNC—A)
C
...
7 — Liquidtight Flexible Metal Conduit (LFMC)
C
...
8 — Rigid Metal Conduit (RMC)
C
...
9 — Rigid PYC Conduit, Schedule 80
C
...
10 — Rigid PYC Conduit, Schedule 40 and HDPE Conduit
C
...
11 — Type A, Rigid PYC Conduit
C
...
12 — Type EB, PYC Conduit
C
...
1 through C
...

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Chapter 6

How to Design a
Lighting System
With the increased concern for energy conservation in recent years,
much attention has been focused on lighting energy consumption and
methods for reducing it
...
This chapter
presents an introduction to lighting design and some of the energy
efﬁcient techniques that can be utilized while maintaining the quality of
illumination
...
By understanding the basics of lighting design, several
ways to improve the efﬁciency of lighting systems will become apparent
...
One is called the
lumen method, while the other is the point-by-point method
...
This
method is used frequently by lighting designers since it is simplest;
however, it wastes energy, since it is the light “at the task” which must be
maintained and not the light in the surrounding areas
...

Point-by-point Method
The point-by-point method makes use of the inverse square law,
which states that the illuminance at a point on a surface perpendicular to
the light ray is equal to the luminous intensity of the source at that point
divided by the square of the distance between the source and the point of
calculation, as illustrated in Formula 6-1
...

Θ = Angle between the source and the point of calculation
...
From this deﬁnition,
the lumen method is developed and illustrated by Formula 6-2
...

F1 is the required footcandle level at the task
...

A is the area of the room in square feet
...
A lumen is a measure of lamp
intensity; its value is found in the manufacturer’s catalogue
...
It represents the ratio of the lumens
reaching the working plane to the total lumens generated by the
lamp
...
Its
values are found in the manufacturer’s catalogue
...
It takes into account that the
lamp lumen depreciates with time
...

L2 is the luminaire (ﬁxture) dirt depreciation factor
...

L3 is the lamp burn out factor

How to Design a Lighting System

169

The lumen method formula illustrates several ways lighting
efﬁciency can be improved
...
The multitude
of equipment options to meet one or more of the above needs permits
the consumer and the lighting designer-engineer to consider the trade-offs
between the initial and operating costs, based upon product performance
(life, efﬁcacy, color, glare, and color rendering)
...
Then, some state-of-the-art advances will be
characterized so that their beneﬁts and limitations are explicit
...
It is a measure of the efﬁciency of a
process, but it is a term used in place of efﬁciency when the input (W) has
different units than the output (lm) and expressed in lm/W
...
Incandescents have a low color temperature (~2800°K) and have a
red-yellowish tone; daylight has a high color temperature (~6000°K) and
appears bluish
...

Color Rendering is a parameter that describes how a light source
renders a set of colored surfaces with respect to a black body light source
at the same color temperature
...
It depends upon the speciﬁc wavelengths of which the light is
composed
...
Fluorescent lamps and high intensity
discharge lamps (HID) have a spectrum rich in certain colors and devoid
in others
...
The same material would appear
*Source: Lighting Systems Research, R
...
Verderber

170

Efﬁcient Electrical Systems Design Handbook

different when viewed with an incandescent lamp, which has a spectrum
that is rich in red
...
Each of these sources is discussed brieﬂy here
...
To obtain the total
system efﬁcacy, ballast input watts must be used, rather than lamp watts,
to obtain an overall system lumen per watt ﬁgure
...

Incandescent lamps have the lowest lamp efﬁcacies of the commonly
used lamps
...
However,
this does not mean that incandescent lamps should never be used
...

General service incandescent lamps do not have good lumen
maintenance throughout their lifetime
...

Efﬁcient Types of Incandescents for Limited Use
Attempts to increase the efﬁciency of incandescent lighting while
maintaining good color rendition have led to the manufacture of a number
of energy-saving incandescent lamps for limited residential use
...
Halogen gases keep the glass
bulb from darkening by preventing the ﬁlament’s evaporation, thereby
increasing lifetime up to four times that of a standard bulb
...
Knott

How to Design a Lighting System

Figure 6-1
...
Tungsten
halogen lamps may require special ﬁxtures, and during operation the
surface of the bulb reaches very high temperatures
...
Sealed tungsten halogen lamps are also available for
car headlamps
...
Certain incandescent light ﬁxtures,
such as recessed or directional ﬁxtures, trap light inside
...
In these ﬁxtures, a 50-watt reﬂector
bulb will provide better lighting and use less energy when substituted for
a 100-watt standard incandescent bulb
...
Reﬂector lamps
are available in 25, 30, 50, 75, and 150 watts
...
(See Figure 6-2)
...
They are available in 75, 150, and 250
watts
...

ER Lamps (ellipsoidal reﬂector lamps) are ideally suited for recessed
ﬁxtures, because the beam of light produced is focused two inches ahead
of the lamp to reduce the amount of light trapped in the ﬁxture
...
(See Figure 6-2
...
Typical
ratings for mercury vapor lamps range from about 30 to 70 lumens per
watt
...
Mercury vapor lamps
are not common, as they have been replaced by ﬂuorescent and higher
efﬁcacy HID sources
...
Several styles of low

How to Design a Lighting System

173

Figure 6-2
...
Lamp
efﬁcacy now ranges from about 30 lumens per watt to near 90 lumens
per watt, or more
...
The compact ﬂuorescent lamps (plug-in and screw-in types)
permit design of much smaller luminaries
...
This makes them somewhat less energy efﬁcient
than high pressure sodium
...
While this lamp displays some very desirable
qualities, it also has some distinct drawbacks, including relatively shorter
life for an HID lamp and long restrike time to restart after the lamp has
been shut off
...

High pressure sodium lamps have extremely high efﬁcacy (60-140
lumens/watt) in a lamp that operates in ﬁxtures having construction very
similar to those used for metal halide
...
The 24,000-hour lamp life, good lumen
maintenance, and high efﬁcacy of these lamps make them ideal sources
for industrial and outdoor applications where discrimination of a range of
colors is not critical
...
The
lamp produces a high percentage of light in the yellow range of the spectrum
...
Rendering of reds and
greens shows a pronounced color shift
...
In areas where color selection, matching and
discrimination are necessary, high pressure sodium should not be used
as the only source of light
...
Since both sources have relatively high efﬁcacies, there is not
a signiﬁcant loss in energy efﬁciency by making this compromise
...
This
source will yield a high efﬁciency system; however, it should be used only
with the knowledge that foliage and landscaping colors will be severely
distorted where high pressure sodium is the only, or predominant,
illuminant
...
If this is a problem, it is necessary
for the designer or owner to determine the extent and signiﬁcance of this
problem and what steps might be taken to alleviate it
...

Low pressure sodium lamps provide the highest efﬁcacy of any of the
sources for general lighting, with values ranging up to 180 lumens per
watt
...
This effect results in no color
discrimination under low pressure sodium lighting and is suitable for
use in a very limited number of applications
...
This source has application for either indoor/
outdoor safety or security lighting, as long as color rendering is not
important
...
The xenon lamps produce a very
white light close to a full spectrum light
...
The use of xenon lamps in car
headlights have expanded the lamp’s popularity
...
A major example of LED’s use
is for the trafﬁc and other signaling lamps
...
LEDs often use 15% or less energy than
typical halogen incandescent lamps
...

Quartz Halogen Lamps—Use quartz crystal encapsulation rather than
boron silica glass
...
The
quartz ﬁlled with the halogen gas allows higher burning temperature and
more light out per watts in
...
They are more efﬁcacious than other ballasts
...

An HID electronic ballast system features better lumen maintenance
and lower ballast losses, compared to magnetic HID ballasts
...
As a result, fewer ﬁxtures are required due to

176

Efﬁcient Electrical Systems Design Handbook

lower lamp loss factors in new installations
...
Therefore, metal halide or high pressure sodium lamps can be
retroﬁtted into mercury vapor ﬁxtures, or self-ballasted mercury lamps
can replace incandescent lamps
...

Figure 6-3 presents data on the efﬁcacy of each of the major lamp
types in relation to the wattage rating of the lamps
...

The lamp efﬁcacies discussed here have been based on the lumen
output of a new lamp after 100 hours of operation or the “initial lumens
...
Some lamp types, such as lightly
loaded ﬂuorescent and high pressure sodium, hold up well and maintain
their lumen output at a relatively high level until they are into or past
middle age
...
Lamp Efﬁcacy (Does Not Include Ballast Losses)

How to Design a Lighting System

177

useful life
...

Incandescent Replacement
The most efﬁcacious lamps that can be used in incandescent sockets
are compact ﬂuorescent lamps
...
These are closer to the size and weight
of the incandescent lamp than the earlier type of ﬂuorescent (circline)
replacements
...
Table 6-1 lists the characteristics
of various types of incandescent and compact ﬂuorescent lamps that can
be used in the same type sockets
...
Lamp Characteristics

————————————————————————————————
Lamp Type
(Total Input Power) *

Lamp Power
(W)

Light Output
(lumens)

Lamp Life
(hour)

100
75
60
40
25
18
36
5
7
9
13
—

1750
1200
890
480
238
870
1750
240
370
560
850
1100

750
750
1000
1500
2500
9000
9000
10000
10000
10000
10000
7500

Efﬁcacy
(lm/W)

————————————————————————————————
100 W
75 W
60 W
40 W
25 W
22 W
44 W
7W
10 W
13 W
19 W
18 W

(Incandescent)
(Incandescent)
(Incandescent)
(Incandescent)
(Incandescent)
(Fl
...
Circline)
(Twin)
(Twin)
(Twin)
(Twin)
(Solid-State)**

18
16
15
12
10
40
40
34
38
43
45
61

————————————————————————————————
*Includes ballast losses
...

The advantages of the compact ﬂuorescent lamps are larger and
increased efﬁcacy, longer life, and reduced total cost
...
00 and $6
...
This is based upon an energy
cost of $
...
The circline lamps were much larger and heavier
than the incandescents and would ﬁt in a limited number of ﬁxtures
...
However, there are some ﬁxtures that are too small for
them to be employed
...
These phosphors improve
lumen depreciation at high lamp power loadings
...
By proper mixing of these phosphors, the color characteristics
(color temperature and color rendering) are similar to the incandescent
lamp
...
In
one type of lamp system, the ballast and lamp are integrated into a single
package
...
In the integrated system, both the lamp
and the ballast are discarded when the lamp bums out
...
The initial lumen output for the various lamps is
shown in Table 6-1
...

Footcandle Level—The footcandle level required is that level required
at the task
...
Footcandle levels can be
lowered to one third of the levels for surrounding areas such as aisles
...
)
The placement of the lamp is also important
...

Coefﬁcient of Utilization (Cu)—The color of the walls, ceiling, and
ﬂoors, the type of luminaire, and the characteristics of the room determine
the Cu
...
The
Cu can be improved by analyzing components such as lighter colored
walls and more efﬁcient luminaires for the space
...
Choosing a luminaire
which resists dirt buildup, group relamping, and cleaning the luminaire
will keep the system at optimum performance
...

The Light Loss Factor (LLF) takes into account that the lamp lumen
depreciates with time (L1), that the lumen output depreciates due to dirt
buildup (L2), and that lamps burn out (L3)
...

LLF = L1 × L2 × L3

Formula (6-3)

To reduce the number of lamps required, which in turn reduces
energy consumption, it is necessary to increase the overall light loss factor
...
One is to choose the luminaire
which minimizes dust buildup
...
Thus, if it is known that a group
relamping program will be used at a given percentage of rated life, the
appropriate lumen depreciation factor can be found from manufacturer’s
data
...
If a group relamping program is used, (L3) is
assumed to be unity
...
Every luminaire has a tendency for dirt buildup
...

Solid-state Ballasts
Fluorescent lamps at high frequency (20 to 30 kHz) with solid-state
ballasts have achieved credibility
...
Effect of Dirt Buildup on Dustproof Luminaires for Various
Atmospheric Conditions

180

Efﬁcient Electrical Systems Design Handbook

have designed new lamps to be operated at high frequency is evidence
that the solid-state high frequency ballast is now state-of-the-art
...
In addition,
the solid-state ballast is more efﬁcacious than conventional ballasts in
conditioning the input power for the lamps, such that the total system
efﬁcacy increase is between 20 and 25 percent
...

Continued development of the product has improved reliability and
reduced cost
...
These multi-lamp ballasts reduce
the initial cost per lamp, as well as the installation cost, and are even more
efﬁcient than the one- and two-lamp ballast system
...
The ballast factor is one parameter
that will be speciﬁed by ANSI
...
The ballast factor is the light output provided
by the ballast-lamp system compared to the light output of the lamp
speciﬁed by the lamp manufacturer
...
5 percent
...
These ballasts are most effectively used in new installations
...
It is essential that the lighting designer/engineer and consumer
know the ballast factor for the lamp-ballast system
...
For example, a core-coil ballast
will have a ballast factor of 95 ± 2 percent when operating a 40-watt F40
argon-ﬁlled lamp, and less when operating an “energy saving” 34-watt
F40 Krypton-ﬁlled lamp
...
5
percent with the 34-watt energy saving lamp
...
Notice that the system efﬁcacy of any ballast
system is about the same operating a 40-watt or a 34-watt F40 lamp
...
The lite white

How to Design a Lighting System

181

phosphor is more efﬁcient than the cool white phosphor but has poorer
color rendering characteristics
...
A scientiﬁc ﬁeld
study of ofﬁce workers in the U
...
showed that complaints of headaches
and eye-strain are 50 percent less under high frequency lighting when
compared to lamps operating at 50 cycles, the line frequency in the U
...

Table 6-2
...
5
6050

...
6
5060

...
1
5870

...
1
5060

...
0
11,110

...
6
9250

...
003
1
90

————————————————————————————————
Each of the above ballasts has different factors, which are lower when
operating the 34-watt Krypton-ﬁlled lamp
...

All of the above solid-state ballasts can be used in place of core-coil
ballasts speciﬁed to operate the same lamps
...
The varied light output from
the various systems allows the lighting designer/engineer to precisely
tailor the lighting level
...
Included in the table is the T-8, 32-watt lamp system, which
has an efﬁcacy of 90 lumens per watt
...
The table uses realistic average costs for the ballasts and
lamps
...
The cost of
ﬂuorescent systems is much less than incandescent lamps systems
...
Static equipment can alter
light levels semipermanently
...
Different sets of components can be used to form various lighting
control systems in order to accomplish different combinations of control
strategies
...
Lighting Control Equipment

————————————————————————————————
System

Remarks

————————————————————————————————
STATIC:
Delamping
Impedance Monitors

Method for reducing light level 50%
...

DYNAMIC:
Light Controllers
Switches/Relays

Method for on-off switching of large banks of lamps
...

Solid-State
Dimming Ballasts

Ballasts that operate ﬂuorescent lamps efﬁciently and can
dim them continuously (100 to 10%) with low voltage
...

Personnel

Sensor that detects whether a space is occupied by sensing
the motion of an occupant
...

COMMUNICATION:
Computer/Microprocessor

Power-Line Carrier

Method for automatically communicating instructions
and/or input from sensors to commands to the light
controllers
...

————————————————————————————————

How to Design a Lighting System

183

FLUORESCENT LIGHTING CONTROL SYSTEMS
The control of ﬂuorescent lighting systems is receiving increased
attention
...

Personnel Sensors
There are three classiﬁcations of personnel sensors-ultrasonic,
infrared and audio
...
Ultrasonic sensor systems are
generally made up of a main sensor unit with a network of satellite
sensors providing coverage throughout the lighted area
...
Sensors may be mounted above the ceiling, suspended
below the ceiling, or mounted on the wall
...
Advertised savings range from 20 to
40 percent
...
Coverage
is limited to approximately 130 square feet per sensor
...
They
can be tied into the HVAC control and limit its operation also
...

Audio sensors monitor sound within a working area
...

Some models advertise coverage of up to 1,600 square feet
...

Advertised energy savings are approximately the same as the ultrasonic
sensors
...
First,
normal background noise must be less than 60 dB
...

Lighting Compensators
Lighting compensators are divided into two major groups switched
and sensored
...
These particular systems are used frequently in
residential settings and are commonly known as “dimmer switches
...
The estimated
savings are difﬁcult to determine, as usually switched control systems are
used to control room mood
...

Sensored compensators are available in three types
...
They may be integrated with the building’s energy
management system or installed as a stand-alone system
...
This system senses
daylight levels and automatically turns off lights as the sensed light level
approaches a programmed upper limit
...
8 to 3
...

The second type of system is the daylight compensator (DAC)
system
...
Advertised savings range from
40 to 50 percent
...
The third system
type is the daylight compensator + excess light turn-off system
...

It automatically dims light outputs to achieve a designated light level and,
as necessary, automatically turns off lights to maintain the desired room
conditions
...
The specular reﬂector
material types are aluminum, silver and multiple dielectric ﬁlm mirrors
...

Measurements show the ﬁxture efﬁciency with higher reﬂectance
specular reﬂectors (silver or dielectric ﬁlms) is improved by 15 percent
compared to a new ﬁxture with standard diffuse reﬂectors
...
This increases the light modulation
in the space, which is the reason several light readings at different sites
around the ﬁxture are required for determining the average illuminance
...

When considering reﬂectors, information should be obtained on
the new candle power characteristics
...

How to Design a Lighting System

185

LIGHTING DESIGN
In the previous section, it was seen that a lamp produces an amount
of light (measured in lumens) that depends on the power consumed and
the type of lamp
...
Luminaires, or lighting ﬁxtures, are used to direct the
light to a usable location, depending on the speciﬁc requirements of the
area to be lighted
...

The coefﬁcient of utilization, or CU, is a factor used to determine
the efﬁciency of a ﬁxture in delivering light for a speciﬁc application
...

Luminaire manufacturers provide CU data in their catalogs which are
dependent on room size and shape, ﬁxture mounting height, and surface
reﬂectances
...

To determine the coefﬁcient of utilization, the room cavity ratio, wall
reﬂectance, and effective ceiling cavity reﬂectance must be known
...
To
determine the coefﬁcient of utilization, the following steps are needed:
(a) Estimate wall and ceiling reﬂectances
...

(c) Determine effective ceiling reﬂectance (pCC)
...

Steps (b) and (c)
Once the wall and ceiling reﬂectances are estimated, it is necessary
to analyze the room conﬁguration to determine the effective reﬂectances
...
Figure 6-5 indicates the
basic cavities
...
The space
between the work plane and the ﬂoor is the ﬂoor cavity
...
To determine the cavity
ratio, use Figure 6-5 to deﬁne the cavity depth, and then use Formula 6-4
...
Typical Lamp Vendor Data

Efﬁcient Electrical Systems Design Handbook

How to Design a Lighting System

187

Table 6-5
...
75

...
30

...
Cavity Conﬁgurations

5 × d × (L+W)
Cavity Ratio = ———————
L×W

(Formula 6-4)

Where
d = Depth of the cavity as deﬁned in Figure 6-5
L = Room (or area) length
W = Room (or area) width
To determine the effective ceiling or ﬂoor cavity reﬂectance, proceed
in the same manner to deﬁne the ceiling or ﬂoor cavity ratio, then refer
to Table 6-4 to ﬁnd the corresponding effective ceiling or ﬂoor cavity
reﬂectance
...
1, determine the coefﬁcient of utilization for a
room which measures 24’ × 100'
...
The tasks in the room are performed on work
benches 3' above the ﬂoor
...

Efﬁcient Electrical Systems Design Handbook

188

Answer

Step (a)
Since no wall or ceiling reﬂectance data were given, assume a ceiling
of
...
5
...

hrc = 20-4-3 = 13 (from Figure 6-5)
From Formula 6-4, RCR = 3
...
64 (interpolated)
FIXTURE LAYOUT
The ﬁxture layout is dependent on the area
...
The end ﬁxture
should be located at one half the distance between ﬁxtures
...
Figure 6-6 illustrates a typical
layout
...
Since the ﬁxtures are 4 feet or 8 feet long, a continuous
wireway will be formed
...
Typical Fixture Layout

How to Design a Lighting System

189

SIM 6
...
The
light loss factor is estimated to be 0
...
The initial lumen output is 8,500 per
lamp
...
of ﬁxtures =

Area × Desired Maintained Footcandle
——————————————————
Lumens × CU × LU

24 × 100 × 50
= ————————
8,500 × 0
...
7

31
...
5
6
(b)
3
11
9
8
(c)
2
16
6
12
(a)

8X = 100
(b)
11X = 100
(c)
16X = 100
X = 12
...
2
4Y = 24
3Y = 24
2Y = 24
Y=6
Y=8
Y = 12
————————————————————————————————————

Alternate (b) is recommended, even though it requires one more
ﬁxture
...

190

Table 6-6
...
This load includes ﬁxture voltage and ballast loss
...
12 gauge wire, eight lamps could be fed from each
circuit breaker
...
(Note:
In practice, ballast loss should be based on manufacturer’s speciﬁcations
...

Figure 6-7
...
e
...

SIM 6-4

Designate a hot line from the circuit breaker with a small stroke and
use a long stroke as a neutral; i
...
, ——— 4 wires, 2 hot and 2 neutrals
...
Designate the hot and
neutrals in each branch
...

POINTS ON LIGHTING DESIGN
•
•
•
•
•

Identify all symbols for lighting ﬁxtures
...

Include a note on ﬁxture mounting height
...
(“Homerun” indicates the
number of wires and conduit size from the last outlet box
...
For example, all wires shall be 2 #12 in 3/4”
conduit unless otherwise indicated
...

LIGHTING QUALITY
Illumination levels calculated by the lumen and point methods at
best give only a “ballpark” estimate of the actual foot candle value to be
realized in an installation
...

Precise illumination levels are not critically important, however
...
Very few people
can perceive a difference of plus or minus ten footcandles, but poor quality
lighting is readily apparent to anyone and greatly affects our ability to
comfortably “see” a task
...

Figure 6-8 shows the two types of glare normally encountered
...
Direct glare also can be caused by light sources, including

How to Design a Lighting System

195

Figure 6-8
...
A rating system called Visual
Comfort Probability (VCP) has been developed for assessing direct glare
...

Most manufacturers publish VCP tables for their ﬁxtures
...
Table 6-7 shows a typical VCP table
...
When the light bounces off a task surface, details of the task
surface become less distinct because contrast between the foreground and
background, such as the type on this page and the paper on which it is
printed, is reduced
...

This form of indirect glare is called a veiling reﬂection because its
effects are similar to those that would result if a thin veil were placed
between the worker’s eyes and the task surface
...
(Generally, to the side and slightly behind
the work position gives the best results)
...
Note that in selecting ﬁxtures to minimize
indirect glare, care must be taken not to select ﬁxtures that are a
source of excessive direct glare
...
By tailoring illumination levels to the various
tasks in an area, signiﬁcant energy savings are possible
...

For this area compute the number of lamps required, the space
between ﬁxtures, and the circuit layout
...
7, 110-volt lighting
system, 20-watt ballast loss per ﬁxture, and a ﬁxture length of 2’ × 4'
...

Table 6-8
...
33

...
22

...
26

...
43

...
27

...
35

...
58

...
35

...
42

...
58

...
42

...
48

...
64

...
49

...
54

...
72

...
59

...
60

...
77

...
64

...
65

...
82

...
70

...
69

...
87

...
77

...
74

...
91

...
83

...
78

...

Assume hfc = 3
hcc = 3 Therefore,
hrc = 14

Efﬁcient Electrical Systems Design Handbook

198

Assume

70% ceiling reﬂectance
50% wall reﬂectance

The room cavity ratio is 7 and the effective ceiling cavity ratio pcc = 53
...
55
...
of Fixtures = ————————— =7
2 × 2900 ×
...
70
Each 20 amp lighting circuit can provide power for up to 16 ﬁxtures
...
6
3y = 18−1/2'
y = 6'2"

Note:

With emphasis on energy conservation, a lighting layout using six
ﬁxtures may be preferable
...
Increased
emphasis is being placed on minimizing lighting loads by using lamps and
luminaries that have high lumen outputs and coefﬁcients of utilization
...
Lighting
systems need to be analyzed on a ﬁrst and operating cost basis to ensure

How to Design a Lighting System

199

that the increasing energy costs are taken into account
...
The choice of a luminaire and its location play
an important part in comfortably perceiving a task
...

“This page left intentionally blank
...

Standard contactors, timing devices, relays, and other provide control
functions
...
Learn the logic language, a way for
communicating
...
Contacts physically
located on the relay will either open or close when the relay coil is
energized
...

Push buttons—Devices which are used to actuate a control system,
i
...
stop-start push buttons
...

Plug-in type relays and prepackaged solid-state components are
widely used
...
These symbols are based on the Joint Industrial
Council (JIC) Standards
...
Notice
that line identiﬁcations on the left are used as references to locate relay
contacts on the right
...

Steps for Analyzing Electrical Control Circuits
Look at one line of operation at a time
...
Every contact to the left of the
electrically operated line must be closed for the device to operate
...

•

Numbers at the right of the line, next to a relay, show on what lines
the device has contacts
...

Simple Control Schemes
In order to control a motor, a starter is required
...
HCA represents the holding coil or contactor of the starter
...

If the stop-start push button were located locally, three wires,
numbers 1, 2, 3 would need to run from the ﬁeld to the MCC
...
, 110 volts would be required
...
)
Lockouts
Two typical lockout schemes are illustrated in Figure 7-4
...
Electrical Symbols

203

204

Efﬁcient Electrical Systems Design Handbook

Figure 7-2
...
Elementary Diagram for a FVNR Motor

running
...

Scheme “B” illustrates the case where once Motor “B” is running
it does not matter if Motor “A” stops
...
”

Using Logic to Simplify Control Systems

205

Figure 7-4
...
Figure 7-5 illustrates the elementary for
a reversing motor
...

Two-speed Motors
To change the speed of the motor requires changing the effective
number of poles
...
Six power leads are required to
change the windings
...
The control portion of the elementary
is similar to that of a reversing motor (Figure 7-5), except that six overloads
are required
...

DESCRIPTION OF OPERATION AND
LOGIC DIAGRAMS
To describe how a process operates it is necessary to establish a logic
diagram or description of operation
...

206

Efﬁcient Electrical Systems Design Handbook

Figure 7-5
...

The HVAC design is as follows:
(a) When exhaust fan #1 is operated, damper EP valve is energized
(electric to pneumatic)
...

Answer

Using Logic to Simplify Control Systems

207

Figure 7-6
...

When level switch LCH #1 in Tank “A” reaches “high” level, Pump
#3 is started
...

Pump #4, which feeds Tank “A,” can be started manually and will
automatically stop when high level occurs (LCHA)
...
When Valve
“A” is energized, Valve “C” cannot be energized
...
Once Valve “C”
is energized, Valves “A” and “B” have no effect
...
Another point is that several people may interpret the
above descriptions differently
...

LOGIC DIAGRAMS AND LOGIC CONTROLLERS
Logic diagrams use symbols to describe the operation, whereas
the elementary diagram uses more words
...
To describe a process, the logic diagram uses symbols
for the three words “And,” “Or,” and “Not
...
Figure 7-7 illustrates symbols commonly
used in logic
...

It is possible to design a complete electrical control scheme by using
a programmable logic controller (PLC) diagram
...
Unlike relays,
they are not hard-wired, so changes in operation can be readily made by
just reprogramming the unit
...

Using Logic to Simplify Control Systems

Figure 7-7
...
They are also useful in the development of
conventional control schemes, since they offer a visual tool that can be
understood not only by the electrical engineer, but by the process and
mechanical engineer as well
...
This in itself can minimize costly design changes
...
When time delays are incorporated
into the design, it is necessary to determine the “state” of the process at
various time periods
...

A “1” indicates a signal present, and a “0” indicates the absence of
a signal
...
The logic
elements can be combined in any order to describe the electrical circuit
...

Answer

Step I Identify initial operating and ﬁnal state of logic
...
Note that two signals from switch “A” are used
...
Both signals are required to give a
pulse after the switch is closed
...

What will happen when SE
...

212

Efﬁcient Electrical Systems Design Handbook

Answer

How to Analyze Logic
(a) Determine the initial condition with switch open
...

(c) Always check the ﬁnal state to see if logic resets
...

SIM 7-5

From the description of operation, draw a logic diagram and an
elementary
...

In order for the compressor (C-1) to operate, the oil oump (P-2)
should be running for ﬁve minutes
...

2
...

3
...
(Stop same as 2
...

When the compressor is shut down, auxiliary oil pump will
automatically come on and automatically stop after ﬁve minutes
...

If high pressure occurs, the compressor will automatically stop
...

7
...

A manual STOP-START push button for the compressor is
provided
...

Since the compressor is the simpler scheme, ﬁrst draw the compressor
logic
...
Since Step 4 also automatically stops the
motor, this step must be drawn independently of the seal in contact
...

Using Logic to Simplify Control Systems

215

INTERCONNECTION DIAGRAMS
To show the electrician how to wire from an elementary diagram,
a physical arrangement referred to as an interconnection diagram is
made
...
Each wire on the elementary is assigned a wire number
...
The
electrician needs only to connect the terminals together with the control
cable
...
Wire numbers and terminal numbers have the same designation as
indicated
...
1
...
1
...
1
...
When
CF-3 is reversing, the transfer pump TP-5 can not be operated
...
Push buttons for C-16 and CF-3 are located on Panel
No
...
Push buttons for TP-5 are locally mounted
...
These motors can be started locally and at the
MCC
...

Efﬁcient Electrical Systems Design Handbook

218

SIM 7-6 Answer:

Assume type THW wire and minimum size is #14
...

Common wires will be jumped locally
...
1 to Panel No
...

From MCC No
...
1
...
1 to local devices

Using Logic to Simplify Control Systems

219

(NOTE: local push buttons are excluded since those cables
were sized in Job 5)
...

Illustrated elementary [see (c)] for motors AG-1, FP-4, CT-9, UH-12
and RD-22
...
In many plants the elementary
diagram is the only document that describes how a process works
...
The verbal description that is the input to the elementary
diagram can be easily misinterpreted
...

The electrical engineer can then use the logic diagram as the basis for his
design
...

Solid-state logic or programmable controllers can be obtained from
the logic diagram
...
The individual who understands the
fundamentals of the logic elements can easily apply this important tool in
developing complex industrial and power elementary control schemes
...
”

Chapter 8

Applying Process
Controllers and
Electronic Instrumentation
The basic requirement for developing electrical schematics is to understand the process
...
In the past,
the hardware used to accomplish this logic was a combination of heavyduty machine tool relays
...
In addition, the current trend is to control process variables (i
...
, temperature,
pressure, ﬂow level) by electronic instrumentation loops
...

PROGRAMMABLE LOGIC CONTROLLER
The programmable logic controller (PLC) developed out of the needs
of the automotive industry
...
Out of these requirements developed the ﬁrst series of programmable controllers
...

The memory was capable of expansion to a maximum of 4000 words
...
Let’s examine some of the features of most models
...
“Brick” Logic Controller

Figure 8-1b
...
Logic Controller with Rack and Numerous Modules
Figures above used with permission of Automation Direct

Applying Process Controllers and Electronic Instrumentation

225

Figure 8-1d
...
Automation Direct Programmable Logic Controller Mnemonics and Ladder

Efﬁcient Electrical Systems Design Handbook

226

•
•
•
•
•

Input module
Memory
Processor
Output module
Programming auxiliary

Input Module
The input module usually accepts AC or DC signals from remote devices such as pushbuttons and switches
...

Processor
This module is the working portion of the PLC
...
The status of the input is compared
against an established program, and instructions are executed to the various outputs
...
An internal timing device determines the
required sequence to fetch and execute instructions
...
Information is usually stored on magnetic
cores
...
Components of a Programmable Controller

Applying Process Controllers and Electronic Instrumentation

227

Output Module
The output module provides the means to command external machine devices
...

Many units have input and output lights on the unit that indicate the
status of the remote devices
...
In either case, the logic or elementary is
directly programmed into the unit
...

Use of a PC with Software
A program can be stored in a personal computer (PC), allowing
the program to be developed in one location and transferred to the site
...

Another feature of programming is in elementary simpliﬁcation and
simulation
...
Typical Keyboard for Programmable Controller

228

Efﬁcient Electrical Systems Design Handbook

in a standard elementary simpliﬁcation program
...
The PC can also be used in conjunction with a
simulation program
...
To change sequence
of operation, the memory is simply reprogrammed
...
The basic functions are:
•

Logic Gates—For a review of logic, see Chapter 7
...
Typical ranges
...
9
seconds
...
Counter size is 999 counts
...

•

Shift Registers—Provide the ability to simultaneously remember
the state of several pieces as they move through the manufacturing
process
...

Applications
There are many PLCs available
...
The
size of the input-output and logic capabilities also varies
...

A highly reliable solid state control that minimizes downtime
...

A system compatible with computer simpliﬁcation and simulation
techniques
...

Applying Process Controllers and Electronic Instrumentation

229

INSTRUMENTATION
Modern process control mostly uses electronic instrumentation
...

Closed Loop
To control a process requires a closed loop system
...
Figure 8-4
shows a typical closed loop system
...

Figure 8-5 shows a typical process control diagram illustrating level
control
...
If the level is too low, control
valve CV-1 is throttled
...
Thus, the process is controlled
...

Signal
In electronic instrumentation the standard signal used to convey

Figure 8-4
...
Typical Level Control Process

process variables is 4-20 ma DC
...

This means that a full-scale level reading corresponds to 100%
...

Control Loop
The basic control circuitry for electronic instrumentation is illustrated in Figure 8-7
...
Each receiving element contains an input impedance
...

DIRECT DIGITAL CONTROL
Process controllers are beginning to be used to make not only logic decisions but also control loop decisions
...
Such a
conﬁguration is often called direct digital control (DDC), since the control
action is determined by the program within the controller
...

Applying Process Controllers and Electronic Instrumentation

231

Figure 8-6
...
Electronic Signal

Figure 8-7
...

Types of Control Instrumentation
The several common types of control variables are:
•
Level
•
Pressure
•
Flow
•
Temperature

232

Efﬁcient Electrical Systems Design Handbook

Figure 8-8
...
Level could
also be controlled by a control valve on process line No
...
Two common
types of level transmitters are the ﬂoat type and differential pressure
type
...
The signal from FT-1 is sent to FC-1, and control valve CV-1
is either opened or closed
...

Magmeter Type
The magnetic ﬂowmeter is the more expensive of the two
...
As indicated in Figure 8-10, the ﬂuid ﬂowing acts as the conductor, while the pipe is located in the magnetic ﬁeld caused by the ﬁeld
coils
...
Flow Control

Applying Process Controllers and Electronic Instrumentation

233

Figure 8-10
...
Thus the voltage induced by the
moving ﬂuid is brought out by leads for external measurement
...
For
magmeters to work properly, the ﬂuid must conduct electricity, and the
tube must be liquid full
...
The ﬂow rate is calculated
by measuring the differential pressure across the oriﬁce plate
...

Temperature
The thermocouple is one of the most frequently used methods for
measuring temperatures between 500 and 1500°C
...

The operation of a thermocouple is based on the principle that an
electromotive force (emf) is developed when two different metals come
in contact
...
Oriﬁce Flow Meter

the temperature of the junctions
...
Due to the nature of the thermocouple, wire splices should be
avoided
...

Figure 8-12 illustrates a typical thermocouple circuit using a
Galvanometer
...

The resistance temperature device (RTD) is a common device used
in measuring temperatures
...

WIRING METHODS
The type of cable and the installation of instrument signals are based
on the reduction of noise
...
Twisted
control cables are used to reduce magnetic noise pickup from a nearby
noise source
...

Applying Process Controllers and Electronic Instrumentation

Figure 8-12
...
Basic Potentiometer Thermocouple Circuit

235

236

Efﬁcient Electrical Systems Design Handbook
Table 8-1
...

Chapter 9

Protective Relaying for
Power Distribution Systems
Due to possible equipment failure or human error, it is necessary
to provide protection devices
...
The main goal of protection coordination is to isolate the affected
portion of the system quickly while at the same time maintaining normal
service for the remainder of the system
...
Protective devices
such as fuses and circuit breakers have time current characteristics that
determine the time it takes to clear the fault
...

Protective relays are another way of achieving selective coordination and are required to operate power breakers above 600 volts
...
These relays have adjustable settings and can be used to actuate the
opening of circuit breakers under various fault conditions
...

In order to complete the power distribution system, it is necessary to
show on the one-line diagram the protective relaying required and the
breakers affected
...
This
chapter will illustrate typical applications of protective devices
...
Some of the standard designations are listed in Table 9-1
...
This relay is used for overcurrent protection and is
current sensitive
...

Overcurrent relays are available with inverse, very inverse, and extremely inverse time current characteristics
...
The very inverse characteristic is most likely to provide
optimum circuit protection and selectivity with other system protection
devices
...

Figure 9-2 illustrates the characteristics of electromechanical overcurrent protective relays
...

Table 9-1
...
Protective Device Numbering and Functions (Continued)

239

240

Efﬁcient Electrical Systems Design Handbook
Table 9-1
...
Protective Device Numbering and Functions (Continued)

241

242

Efﬁcient Electrical Systems Design Handbook
Table 9-1
...
Protective Device Numbering and Functions (Continued)

243

244

Efﬁcient Electrical Systems Design Handbook
Table 9-1
...
Protective Device Numbering and Functions (Continued)

245

246

Efﬁcient Electrical Systems Design Handbook
Table 9-1
...
Protective Device Numbering and Functions (Continued)

247

248

Efﬁcient Electrical Systems Design Handbook
Table 9-1
...

Figure 9-3 shows a typical electromechanical overcurrent relay schematic
...
For a three-phase circuit, three of these relays are required
...
Notice that protective
relay contacts are connected in parallel so that any one will trip the break-

Protective Relaying for Power Distribution Systems

249

Figure 9-1
...
The control switch (CS) can be manually used to
trip the breaker
...
Figure 9-5 presents
a simpliﬁed protective relay elementary
...
A typical elementary used to close the
circuit breaker is illustrated in Figure 9-6
...
The instantaneous attachment can be used, or it can be disconnected
from service if it is not required
...

THE GROUND OVERCURRENT RELAY (Devices 50N and 50G)
Ground-fault protection has been required since the 1971 NEC
...
Ground overcurrent protection can be provided either by
overcurrent or instantaneous overcurrent relays
...

Figure 9-8 illustrates the residual grounding scheme
...
Characteristics of Overcurrent Relays

Protective Relaying for Power Distribution Systems

251

Figure 9-3
...
The residual relaying scheme detects ground-fault current
by measuring the current remaining in the secondary of the three-phase of
the circuit as transformed by the current transformers
...
Due to the possible unbalances caused by unequal
current transformer saturation on phase faults and transformer energizing inrush currents, the instantaneous overcurrent relay is seldom used
...
This scheme
uses zero sequence current transformers to detect on ground faults the
unbalances in the magnetic ﬂux surrounding the three-phase conductors
...

The instantaneous or overcurrent relay can be used with this scheme
...

With the ground sensing scheme it is possible to detect and clear system
faults as small as 15 amperes
...
Typical Trip Circuit of Protective Relays

The neutral grounding scheme illustrated in Figure 9-10 is used
commonly with resistively grounded transformers
...

PARTIAL DIFFERENTIAL OR SUMMATION RELAYING
This protective relaying scheme is commonly used to detect and isolate faults without affecting other portions of the system
...
In this scheme the
tie breakers are nominally closed
...
Likewise a fault on BUS

Protective Relaying for Power Distribution Systems

Figure 9-5
...
Typical Close Elementary of a Circuit Breaker

253

Efﬁcient Electrical Systems Design Handbook

254

Figure 9-7
...

Residual Grounding Scheme

Figure 9-9
...
One way
of accomplishing this is to connect the current transformers of protective
relays such that they will only pick up when the fault currents through
the pair of current transformers ﬂow in opposite directions
...
The current

Protective Relaying for Power Distribution Systems

255

Figure 9-10
...
Maximum Rating or Setting of Motor Branch-circuit, Short-circuit,
and Ground-fault Protective Devices
...
This reprinted material is not the complete and ofﬁcial position of the NFPA on
the referenced subject, which is represented only by the standard in its entirety
...
, Quincy, MA
...
On the other
hand, a fault on BUS G will cause currents to ﬂow in the same direction
through the current transformers; thus these relays will not operate under
this condition
...
This relay operates on the difference between two currents
...
This ﬁgure shows the differential principle applied to a single-phase
winding of electrical equipment, such as a generator
...
Partial Differential Protective Relay Scheme

Protective Relaying for Power Distribution Systems

257

Figure 9-12
...
The current transformers are connected to the equipment
to be protected
...

The purpose of the restraining coil is to prevent undesired relay operation
as a result of a mismatch in current transformers
...

Notice on Figure 9-12 the introduction of polarity marks on the current transformers
...

Current ﬂows out of the polarity mark for secondary connections
...

See Figure 9-13 for an illustration of polarity marks
...
Polarity and Circuit Diagram

UNDERVOLTAGE RELAY (Device 27) AND
OVERVOLTAGE RELAY (Device 59)
The undervoltage and overvoltage relays are used wherever protection is required for these conditions
...
Figure 9-14 illustrates a one-line diagram for undervoltage and overvoltage relays
...
An auxiliary contact from breaker A trips breaker B
after breaker A is tripped
...
The characteristics of undervoltage relays
are indicated in Figure 9-15
...
Solid-state techniques allow improvement in sensitivity and temperature stability, plus effective transient surge protection
...
One-Line Diagram for Undervoltage and Overvoltage Relay

Figure 9-15
...

Some of the advantages of solid-state relays are summarized below
...
These test buttons allow for
initial settings, operational and wiring checks, and maintenance tests
...
More precise tests can also be made
...
The conventional electromechanical overcurrent relay is the induction disc type
...
There are two methods commonly used to rotate the induction
disc
...
In this method
a portion of the electromagnet pole face is short-circuited by a copper ring
or coil to cause the ﬂux in the shaded portion to lag the ﬂux in the unshaded portion
...
In both methods the moving contact

Figure 9-16
...
In the induction-disc type of overcurrent
relay, the disc continues to rotate after the starting current has decreased
to a low value
...
Solid-state relays do not have rotating parts; thus the problem of
overtravel does not occur
...

The solid-state overcurrent relay consists of printed circuit boards
that produce a DC output voltage when the input AC current exceeds a
given value
...
The overcurrent module consists of a setting circuit, phase-splitter
circuit, sensing circuit, ampliﬁer circuit, feedback circuit and an output
circuit
...

Low Burden
Low-volt ampere (burden) requirements for protective relays mean
that more relays may be connected in series, the lowest tap of a multi-ratio
CT can be used, and the auxiliary CT can be stepped up for residual current
sensitivity
...
Another savings is
that bush-mounted current transformers are not required with solid-state
relays
...

Reduction in Panel Space
A comparison of solid-state relay sizes with their electromechanical
counterparts indicates a space savings of at least one third
...

Improved Indication
The solid-state protective relay has a target which operates independently of the trip-coil current and depends only on the proper functioning
of the relay
...
With the new design it is possible to have an indicator without
a seal-in contact in parallel with the relay’s measuring contacts
...

262

Efﬁcient Electrical Systems Design Handbook

Better Immunity to Shock
Since the solid-state relay has no moving parts, it is in many cases
better suited for earthquake-prone locations
...

Reliability
Solid-state devices are reliable, have good repeatability, and are economical for industrial applications
...
Over the last few
years solid-state protective devices have proved to be a new tool for system protection
...
These solid state electrical relays are ideal for applications that
have many contact closures, since solid state relay switches offer a greatly
extended life compared to electromechanical relays
...

When voltage is applied to the input of the SSR, the relay switch is energized by a light emitting diode
...
”
“In the case of non-zero voltage crossover relays, the output of the
solid state switch is turned on at the precise voltage occurring at the time
...
”
Solid state relays have features which electromechanical relays do
not, such as:
•
•
•

Long life
Shock and vibration resistance
Generation of RFI, EMI

Protective Relaying for Power Distribution Systems

•
•
•
•
•
•

No contact bounce
Arcless switching
Acoustic noise
Zero voltage switching
IC compatibility
Immunity to humidity, salt spray and dirt”*

Figure 9-17
...
”

Chapter 10

Energy
Economic Analysis
To justify the energy investment cost, a knowledge of life-cycle costing is required
...
It takes into account the time value of money and can incorporate
fuel cost escalation into the economic model
...
In other words, the life-cycle cost analysis
considers the cost over the life of the system rather than just the ﬁrst cost
...
The life-cycle cost
analysis takes into account the time value of money; thus a dollar in hand
today is more valuable than one received at some time in the future
...

DEVELOPING CASH FLOW MODELS
The cash ﬂow model assumes that cash ﬂows occur at discrete points
in time as lump sums and that interest is computed and payable at discrete points in time
...

The cash ﬂow model can also be used to ﬁnd the present value of a
future sum F
...

To develop the cash ﬂow model for the “Uniform Series Compound
Amount” factor, the following cash ﬂow diagram is drawn
...

The A dollars deposited at the end of the nth period earn no interest
and, therefore, contribute A dollars to the fund
...
The A dollars deposited at the end
of the (n – 2) period earn interest for 2 years and will, therefore, contribute

Energy Economic Analysis

267

A(1 + i)2
...
The total in the fund F is,
thus, equal to A + A(1 +i)+A(1 +i)2 + A(1 +i)3 + A(1 +i)4 +…+ A(1 +i)n–2 +
A(1 +i)n–1
...
They can be determined from
computer programs and interest tables included in the Appendix
...
In the case of the gradient present worth factor the escalation
rate must also be stated
...

In the present worth method a minimum rate of return (i) is stipulated
...
The alternative with lowest effective ﬁrst cost is the most
desirable
...
The
difference is that the ﬁrst cost is converted to an annual expenditure
...

In the rate-of-return method, a trial-and-error procedure is usually
required
...
The rate-of-return analysis gives a good indication of the overall
ranking of independent alternates
...
Interest Factors

270

Efﬁcient Electrical Systems Design Handbook

The effect of escalation in fuel costs can inﬂuence greatly the ﬁnal
decision
...

Special appreciation is given to Rudolph R
...
Robert
Brown for use of their specially designed interest and escalation tables
used in this text
...
For example, if one alternate
forces additional maintenance or an operating expense to occur, then these
factors, as well as energy costs, need to be included
...
The only factor to
be considered is whether the new cost can be justiﬁed based on projected
savings over its useful life
...
The simple payback is deﬁned as initial investment divided by annual savings after taxes
...

Since the payback period is relatively simple to calculate, and due to
the fact managers wish to recover their investment as rapidly as possible,
the payback method is frequently used
...

When used by itself as the principal criterion, it may result in choosing
less proﬁtable investments that yield high initial returns for short periods,
as compared with more proﬁtable investments which provide proﬁts over
longer periods of time
...
By upgrading the motor spares with high efﬁciency
motors, a 10% savings can be realized
...
Assuming an 8¢ per kWh energy charge and
20-year life, is the expenditure justiﬁed based on a minimum rate of return
of 20% before taxes? Solve the problem using the present worth, annual
cost, and rate-of-return methods
...
87 =
Present Worth

—
4 × 106 ×
...
87
$1,558,400
$1,558,400

(1) + (3)

Annual Cost Method
(1) First Cost (P)
(2) Annual Cost (A)
CR (Table A-4)
(3) P ×
...
2
—
$320,000

Alternate 2
Use High Efﬁciency
Motor Spares
$80,000

...
87
$1,402,560
$1,482,560
Choose Alternate with
Lowest Present Worth Cost

Alternate 2
$80,000
$288,000

...
5
32,000
What value of i will make P/A = 2
...

Example SIM 10-2

the

Show the effect of 10% escalation on the rate-of-return analysis given

Energy equipment investment =
After tax savings
=
Equipment life (n)
=

$20,000
$ 2,600
15 years

Efﬁcient Electrical Systems Design Handbook

272

Analysis

Without escalation

A
2,600
CR = — = ——— =
...

With 10% escalation assumed:
P
20,000
GPW = — = ——— = 7
...

Thus we see that taking into account a modest escalation rate can
dramatically affect the justiﬁcation of the project
...
In other words, for tax
purposes the expenditure for an asset such as a pump or motor cannot be
fully expensed in its ﬁrst year
...
A company wishes to
expense an item as quickly as possible
...

Straight-line Depreciation: The simplest method is referred to as a
straight-line depreciation and is deﬁned as
D=
Where
D
L

P–L
———
n

Formula (10-8)

is the annual depreciation rate
is the value of equipment at the end of its useful life, commonly
referred to as salvage value

Energy Economic Analysis

n
P

273

is the life of the equipment which is determined by Internal
Revenue Service guidelines
is the initial expenditure
...
In this method the depreciation rate is determined by ﬁnding
the sum of digits using the following formula:
N= n

n+1
———
2

Formula (10-9)

Where n is the life of equipment
...

The rate is calculated by taking a constant percentage of the declining undepreciated balance
...
Under certain circumstances a rate equal to 200% of the straight-line depreciation
rate may be used
...
In this method the salvage value or undepreciated book value is established once the depreciation rate is pre-established
...

Salvage value is 0
...

Straight-line Method
D=

P–L
150,000
——— = ———— = $30,000 per year
n
5
Sum-of-years Digits

n(n + 1)
5(6)
N = ——— = —— = 15
2
2
D1 =

n
5
— (P) = —
N
15
N
1=
2=
3=
4=
5=

(150,000) = 50,000
P
$54,000
40,000
30,000
20,000
10,000

Energy Economic Analysis

D = 2 × 20% = 40%
Year
1
2
3
4
5

275

Declining-balance Method
(Straight-line Depreciation Rate = 20%)
Undepreciated Balance
At Beginning of Year
Depreciation Charge
150,000
60,000
90,000
36,000
54,000
21,600
32,400
12,960
19,440
7,776
TOTAL
138,336

Undepreciated Book Value (150,000 – 138,336) = $11,664
Cogeneration Equipment Depreciation
Most cogeneration equipment is depreciated over a 15- or 20-year
period, depending on the particular type of equipment involved, using
the 150% declining balance method switching to straight-line to maximize
deductions
...
Equipment used in
the steam power production of electricity for sale (including combustion
turbines operated in combined cycle with steam units), as well as assets
used to produce steam for sale, are normally depreciated over a 20-year
period
...
Electrical and steam transmission and distribution equipment will be depreciated over a 20-year period
at the same 150 percent declining balance rate
...
Equipment
installed in connection with residential real property qualiﬁes for a 271/2-year period, while equipment placed in nonresidential facilities is
subject to a 31-1/2-year period
...

276

Efﬁcient Electrical Systems Design Handbook

After-tax Analysis
Tax-deductible expenses such as maintenance, energy, operating
costs, insurance and property taxes reduce the income subject to taxes
...
On the other hand, the depreciation allowance
reduces taxes directly
...
This
method analyzes all transactions, including ﬁrst and operating costs
...

The present worth factors tables in the Appendix, can be used for
this analysis
...
The summation of all present dollars should equal zero when the correct interest rate is selected, as illustrated in Figure 10-2
...

Example SIM 10-4

Comment on the after-tax rate of return for the installation of a heatrecovery system, given the following:
• First Cost
$100,000
• Year Savings
36,363
• Straight-line depreciation life and equipment life of 5 years
• Income tax bracket 34%

Energy Economic Analysis

277

Figure 10-2
...
66(36,363) +
...
833

...
578

...
401

PW
–100,000
25,656
21,374
17,802
14,845
12,350
Σ – 7,972

Since summation is negative a higher present worth factor is required
...

Efﬁcient Electrical Systems Design Handbook

278

Investment
0-100,000
1
2
3
4
5

After Tax
Savings
30,800
30,800
30,800
30,800
30,800

SPPW
15%

...
756

...
571

...

3177 + 7972
————— =
–5

3177 – 0
————
15 – i%

3177
i = ——— + 15 = 16
...
6
Impact of Fuel Inﬂation on Life-cycle Costing
As illustrated by SIM 10-2, a modest estimate of fuel inﬂation has a
major impact on improving the rate of return on investment of the project
...
All too often no fuel inﬂation is considered
because of the difﬁculty of projecting the future
...

•
What has been the historical rate increase for the facility? Even with
ﬂuctuations there are likely to be trends to follow
...

•
What do the experts say? Energy economists, forecasting services,
and your local utility projections all should be taken into account
...
Tables A-9 through A-12 can be used to
show the impact of fuel inﬂation on the decision-making process
...
The effect of escalation is not considered
...
A 5% fuel escalation is considered
...
A 10% fuel escalation is considered
...
A 14% fuel escalation is considered
...
A 20% fuel escalation is considered
...

Assume straight-line depreciation over useful life, 34% income tax
bracket, and no tax credit
...
34, E = $1000
0
...

The ﬁrst component is a uniform series of $660 escalating at e percent/
year
...
34P/N
...
The sum
of these two present worth factors must equal P
...
34P
P = 660 P/A + —— P/A
N
In the case of escalation
0
...

The results are indicated below
...
This ﬁgure can be
used as a quick way to determine after-tax economics of energy utilization expenditures
...
Comment on the
investment that can be justiﬁed if it is assumed that the fuel rate escalation should not be considered, the annual energy savings is $2000, and the
equipment economic life is 10 years
...

Answer

From Figure 10-3, for each $1000 energy savings, an investment of
$3600 is justiﬁed (or $8000 for a $2000 savings) for which no fuel increase
is accounted
...

Thus, a 57% higher expenditure is economically justiﬁable and will yield
the same after-tax rate of return of 15% when a fuel escalation of 10% is
considered
...
Effects of Escalation on Investment Requirements

281

Note: Maximum investment in order to attain a 15% after-tax rate of return on investment
for annual savings of $1000
...
”

Chapter 11

Energy Management Systems
ENERGY MANAGEMENT
The availability of computers at moderate costs and the concern for
reducing energy consumption have resulted in the application of computerbased controllers to more than just industrial process applications
...
Equipment controlled can include fans,
pumps, boilers, chillers and lights
...

BASIC TIME CONTROL
One of the simplest and most effective methods of conserving energy
in a building is to operate equipment only when it is needed
...

One of the simplest devices to schedule equipment operation is the
basic timer
...
As is shown in the following
problem, signiﬁcant savings can be achieved through the correct application of basic timers
...

What are the annual savings that result from installing a timer to operate
283

Efﬁcient Electrical Systems Design Handbook

284

these fans from 7:00 a
...
to 5:00 p
...
, Monday through Friday? Assume
an electrical rate of $0
...
8
...
746 kW/hp × (8736-2600) hours × 1/
...
16/
kWh = $119,000
Although most buildings today utilize some version of timer control,
the magnitude of the savings value in this example illustrates the importance of correct timeclock operation and the potential for additional costs
if this device should malfunction or be adjusted inaccurately
...

PROBLEMS WITH BASIC IMERS
Although the use of timers has resulted in signiﬁcant energy savings, they are being replaced by energy management systems because of
problems that include the following:
•

Holidays, when the building is unoccupied, cannot easily be taken
into account
...

•

There are a limited number of on and off cycles possible each day
...

Energy management systems are designed to overcome these problems plus provide increased control of building operations
...
e
...
These devices can control from one to a virtually unlimited number of items of
equipment
...
This ability to maximize energy conservation, while preserving occupant comfort, is the ultimate goal of an
energy engineer
...

Microprocessor-based systems can control from 1 to 40 input/outpoints and can be linked together for additional loads
...
A battery maintains the
programming in the event of power failure
...
)
Capabilities of this type of EMS are generally pre-programmed so
that operation is relatively straightforward
...
g
...
Microprocessor-based EMS
can have any or all of the following capabilities:
•
•
•

Scheduling
Duty Cycling
Demand Limiting

•
•
•

Optimal Start
Monitoring
Direct Digital Control

Scheduling EMS
Scheduling with an EMS is very much the same as it is with a timeclock
...
Unlike a timeclock, however, multiple start/stops can be accomplished very easily and accurately
...
It should be noted that this single function, if accurately pro-

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Efﬁcient Electrical Systems Design Handbook

grammed and depending on the type of facility served, can account for the
largest energy savings attributable to an EMS
...
When the holiday occurs, regular programming is overridden and
equipment can be kept off
...

Therefore, they can sometimes be shut down for short periods each hour
(typically 15 minutes) without affecting occupant comfort
...
Duty cycling saves fan and pump energy but does not reduce the energy required for space heating or cooling since the thermal demand must
still be met
...
If, for example, the desired temperature in an area is 70° and at this temperature equipment is cycled 50
minutes on and 10 minutes off, a possible temperature-compensated EMS
may respond as shown in Figure 11-1
...

Duty cycling is best applied in large, open-space ofﬁces that are served
by a number of fans
...

Duty cycling of fans which provide the only air ﬂow to an area should
be approached carefully to ensure that ventilation requirements are maintained and that varying equipment noise does not annoy the occupants
...
Care should be taken, particularly with motors over
20 hp, to prevent starting and stopping of equipment in excess of what is
recommended by the manufacturer
...
Peak demand is very important to the utility so they may

Energy Management Systems

287

Figure 11-1
...

To determine the peak demand during the billing period, the utility
establishes short periods of time called the “demand interval” (typically
15,30, or 60 minutes)
...
(See Figure 11-2
...
A
ratchet rate means that the billed demand for the month is based on the
highest demand in the previous 12 months, or an average of the current
month’s peak demand and the previous highest demand in the past year
...
The user will get the most electrical energy per dollar if the load is kept constant, thereby minimizing the
demand charge
...

A measure of the electrical efﬁciency of a facility can be found by
calculating the load factor
...

Efﬁcient Electrical Systems Design Handbook

288

Figure 11-2
...
55

The ideal load factor is 1
...
0 gives an indication of the potential for reducing peak demand (and demand charges) at a
facility
...
If the facility demand
is predicted to exceed the user-entered setpoint, equipment is “shed” to
control demand
...

Electrical load in a facility consists of two major categories: essential
loads, which include most lighting, elevators, escalators, and most pro-

Energy Management Systems

289

duction machinery; and non-essential (“sheddable”) loads such as electric
heaters, air conditioners, exhaust fans, pumps, snow melters, compressors
and water heaters
...

To prevent excessive cycling of equipment, most energy management systems have a deadband that demand must drop below before
equipment operation is restored (See Figure 11-4)
...

It should be noted that demand shedding of HVAC equipment in
commercial ofﬁce buildings should be applied with caution
...

Figure 11-3
...
Demand Limiting Actions

Time-of-day Billing
Many utilities are beginning to charge their larger commercial users
based on the time of day that consumption occurs
...
e
...
This is necessary because utilities must augment the power production of their large power plants during periods of peak demand
with small generators that are expensive to operate
...

Optimal Start
External building temperatures have a major inﬂuence on the
amount of time it takes to bring the building temperature up to occupied
levels in the morning
...

During other times of the year, when temperatures are not as extreme,
building temperatures can be up to occupied levels several hours before
HVAC is necessary, and consequently unnecessary energy is used
...
)
Energy management systems with optimal start capabilities, however, utilize indoor and outdoor temperature information, along with
learned building characteristics, to vary start time of HVAC equipment so
that building temperatures reach desired values just as occupancy occurs
...
m
...
m
...
m
...

Most energy management systems have a “self-tuning” capability to
allow them to learn the building characteristics
...
Artiﬁcial intelligence (AI) methods are also incorporated
as part of an EMS
...
Typical Variation in Building Warm-up Times

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Efﬁcient Electrical Systems Design Handbook

Monitoring
Microprocessor-based EMS can usually accomplish a limited amount
of monitoring of building conditions including the following:
•
Outside air temperature
•
Indoor air temperature (with several sensors)
•
Facility electrical energy consumption and demand
•
Several status input points
The EMS can store this information to provide a history of the facility
...

Direct Digital Control
The most sophisticated of the microprocessor-based EMSs provide
a function referred to as “direct digital control” (DDC)
...

Direct digital control is used in the majority of all process control
applications and is an important part of the HVAC industry
...

Control functions previously were performed by a pneumatic controller that received its input from pneumatic sensors (i
...
, temperature,
humidity) and sent control signals to pneumatic actuators (valves, dampers, etc
...
(See Figure 11-6 for a typical pneumatic control conﬁguration
...
Electronic sensors are used to measure variables such as
temperature, humidity and pressure
...
(See Figure 11-6 for a typical DDC conﬁguration
...

Energy Management Systems

•
•

293

Flexibility to easily and inexpensively accomplish changes of control
strategies
...

To program the DDC functions, a user programming language is utilized
...
Comparison of Pneumatic and DDC Controls

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Efﬁcient Electrical Systems Design Handbook

establish parameters and control strategies
...
It accepts operator commands, displays data, and graphically displays systems controlled
or monitored by the EMS
...

A “ﬁeld interface device” (FID) provides an interface to the points
that are monitored and controlled, performs engineering conversions to
or from a digital format, performs calculations and logical operations, and
accepts and processes commands
...

The FID is essentially a microprocessor based EMS, as described previously
...

The FIDs are generally located in the vicinity of the points to be monitored/controlled
...
e
...

In some versions, the FIDs can communicate directly with each other
...
A major disadvantage of this type of “centralized” system is that the loss of the central control disables the entire control system
...
This system, which is prevalent today, utilizes microprocessor-based FIDs to function as remote controllers
...

Each intelligent unit sends signals back to the main unit only upon a
change of status, rather than continuously transmitting the same value as
previous “centralized” systems have done
...
The central unit’s primary function becomes one of directing communications between various FID panels, generating reports and graphics,
and providing operator interface for programming and monitoring
...
For this reason, these systems are

Energy Management Systems

295

sometimes referred to as energy monitoring and control systems (EMCS)
...

The computer based EMS is also designed to make operator interaction very easy
...
In addition, custom programming languages are available so that powerful programs can be created speciﬁcally
for the building through the use of simpliﬁed English commands
...
to better understand building systems
operation
...

Many computer-based EMSs can also easily incorporate ﬁre and security monitoring functions
...
By combining these functions with
energy management, savings in initial equipment costs can be achieved
...

The color graphics display can be particularly effective in pinpointing alarms as they occur within a building and guiding quick and appropriate response to that location
...

Note, however, that the incorporation of ﬁre, security and energy
management functions into a single system increases the complexity of
that system
...
Since the
function of ﬁre monitoring is critical to building operation, these disadvantages must be weighed against the previously mentioned advantages
to determine if a combined BAS is desired
...
These transmission systems include telephone lines, coaxial cables, electrical power lines,
radio frequency, ﬁber optics and microwave
...

Efﬁcient Electrical Systems Design Handbook

296

Table 11-1
...

Effort

Expandability

Compatibility
with Future
Requirements

fast

excellent

min
...

very good

min
...

fast but
limited

low

high

very limited

very limited

Microwave

very
high

very fast

excellent

high

unlimited

unlimited

Telephone

very
low

slow

low to high

min
...

unlimited

unlimited

Power
Line
Carrier

med
...

med
...
A twisted pair consists of two insulated conductors twisted together to minimize interference from unwanted signals
...
To maintain a particular data communication rate, the line bandwidth, time delay, or the
signal-to-noise ratio may require adjustment by conditioning the line
...
By using signal conditioning, operating
speeds up to 9600 bps may be obtained
...

Two of the major problems involve the quality of telephone pairs provided
to the installer and the transmission rate
...
This type of line may be used for increased data
transmission, with the proper line conditioning
...

Coaxial Cable
Coaxial cable consists of a center conductor surrounded by a shield
...
The
shield protects against electromagnetic interference
...

The transmission rate is limited by the data transmission equipment
and not by the cable
...

Power Line Carrier
Data can be transmitted to remote locations over electric power lines
using carrier current transmission that superimposes a low power RF (radio frequency) signal, typically 100 kHz, onto the 60 Hz power distribution system
...
Transmission can be either
one-way or two-way
...
g
...
Figure 11-7 shows a basic power line carrier system conﬁguration
...
RF systems can be effectively used for two-way communication between CPU and FID panels where other data transmission methods
are not available or suitable for the application
...
Power Line Carrier System Conﬁguration

Energy Management Systems

299

es, unitary heaters, and family housing projects
...

Additionally, there may be a difﬁculty in ﬁnding a frequency on which to
transmit, since there are a limited number available
...
The greater
the distance, the greater the likelihood that erroneous signals will be received
...
Fiber optics is a reliable communications
media that is rapidly becoming cost competitive when compared to other
high-speed data transmission methods
...
The signal attenuation of highquality ﬁber optic cable is lower than the best coaxial cables
...
Fiber optics must be carefully installed and cannot
be bent at right angles
...
The
primary drawback of microwave links is initial cost
...

Microwave transmission rates are very fast
...
The only
limit on expansion is cost
...

Capabilities of EMS can include scheduling, duty cycling, demand
limiting, optimal starting, monitoring, direct digital control, ﬁre detection,
and security
...

An energy management system (EMS) may be used for energy management in control of building systems, groups of buildings, and in power
transmission and distribution
...
Most of
these energy management systems provide reading of utility meters for
electricity, gas and water
...

A power transmission EMS is usually a computer based system used
by operators of electric utility grids to monitor, control, and optimize the
performance of the generation and/or transmission system
...
Used with SCADA systems are optimization packages for advanced applications
...

Chapter 12

Power Line Disturbances:
A User’s Perspective on the
Selection and Application of
Mitigation Equipment
Techniques*
INTRODUCTION
The proliferation of personal computers (PCs), programmable logic
controllers (PLCs), energy management systems (EMS), microprocessorbased instrumentation, and other state-of-the-art electronic devices in an
industrial plant setting has prompted a new awareness of the impact of
power line disturbances (PLD) on the reliability of these systems and the
ability to perform the desired tasks in an interruption-free manner
...
This chapter reviews the various
types of power line disturbances and their possible sources
...
Brand names are included to present a cross section of equipment available, and the listing is not intended
to be all inclusive
...
L
...

301

302

Efﬁcient Electrical Systems Design Handbook

There are a variety of ﬁrms capable of supplying satisfactory equipment and services
...

Application of this equipment and services for these speciﬁc requirements should not be construed as a general endorsement by either
Hoechst Celanese Corporation or by the author
...

Background
The challenge is to provide the required power quality for these systems while meeting corporate economic guidelines
...
Electronic loads require cleaner power
...
These same
power disturbances can also shorten the expected life of an electronic device by causing increased heating and higher electrical stress
...
For example, in a typical electronic instrument the power supply is 5% of the cost; but in a power disturbance monitoring instrument designed to tolerate almost any power
disturbance, the power supply’s cost rises to as much as 30%
...
This approach is costly and is effective only
when the load is concentrated in one physical location (such as a room
dedicated to a mainframe computer)
...

Table 12-1 illustrates typical electronic requirements vs
...
1

Power Line Disturbances

303

Table 12-1
...
Utility Speciﬁcations

————————————————————————————————
Power
Disturbance
Event

Typical Electronic
Load Requirements

Typical Utility
Delivery Speciﬁcation

Voltage surge

No more than 10% for no longer than
32 milliseconds

No more than 20% for
no longer than 60 ms

Voltage sag

No more than 13% for no longer than
200 milliseconds

No more than 20% for
no longer than 500 ms

Impulse

No more than 200 Vpk for no longer
than 20 microseconds

Not speciﬁed

Noise

No more than 5 V pk-to-pk
between 100 KHz and 2 MHz

Not speciﬁed

————————————————————————————————

————————————————————————————————
(The utility delivery speciﬁcation applies at the service entrance to the
building
...
)
Responsibility for Power Quality
The end-user is responsible for providing an acceptable operating
environment for the electronic load
...

Many electronics suppliers have a weak or non-existent pre-site inspection requirement, even to the point of stating their electronic loads will
operate from “standard” power
...
” Other suppliers explicitly state their power requirements, including tolerance levels for common
power quality faults, However, explicit power quality requirements are virtually impossible to measure unless the end-user or ﬁeld service engineer is
equipped with the proper training, procedures, and instrumentation
...
Also, if any action
plan is to be formulated to deal with these disturbances, it is important to
know something about their sources and the effects they have on equipment and computer hardware
...
Voltage variations include brownouts, which are intentional reductions by the utilities to conserve energy for a speciﬁc period of
time
...
Voltage variations are caused by unregulated utility feeders that experience changes
in load over a period of time
...

Powerfail
Powerfail is deﬁned as the total removal of input voltage for at least
5 milliseconds
...
Some disc drives have heads which automatically retract upon loss of power, but it is not safe to assume this without checking
the equipment speciﬁcations
...
The length of powerfail a computer or
other equipment can tolerate will depend on the size of the backup logic
battery onboard, or the ride-through provided by the LC ﬁltering circuit
of the power supply, and the load on the power supply at the time of the
powerfail
...
Often large AC motors connected to the same
power system will act as generators for a few cycles to provide additional
ride-through
...
The most common powerfail is that caused by utility reclosing circuit breakers acting to clear lightning-induced ﬂashover, or a

Power Line Disturbances

305

fault caused by a powerline coming in contact with a tree branch or other
grounded object
...
Large SCRs used in DC and adjustable-speed AC
motor drives can “notch” the sine wave, causing what amounts to a short
powerfail
...
This term is also
often used loosely to describe any disturbance that is transitory, such as
common-mode noise, surges, sags, and other phenomena
...

The effect of transients on the computer can be data errors, due to the
spike voltage passing through the interwinding capacitances of the power
supply and on to the logic circuits
...

Surges and Sags
Of all the jargon used to describe power system disturbances, the
word “surge” is probably the most misunderstood
...
The IEEE deﬁnes a surge as a transient wave of voltage or
current
...

Of all the types of power line disturbances, surges are perhaps the least
common and the least troublesome
...

A sag is a sudden reduction in voltage greater than 1/2 cycle in duration, and it is most frequently caused by faults being cleared on the utility line and the starting of large motors across-the-line within the plant
...

306

Efﬁcient Electrical Systems Design Handbook

Harmonic Distortion
One of the greatest causes of harmonic distortion in today’s power
systems is SCR switching
...
Often the computer
power supply is the worst offender
...

Motor, incandescent lighting, and heating loads are linear in nature
...
For alternating current, the current increases proportionately as the voltage increases, and it decreases proportionately as the
voltage decreases
...

In the past, most loads were linear, and the non-linear loads were a
small portion of the total as to have little effect on the system design and
operation
...
These electronic loads are
mostly nonlinear and are a large factor to have serious consequences on
distribution systems
...

A nonlinear load is one in which the load current is not proportional
to the instantaneous voltage
...
It
can be switched on for only part of the cycle, as in a thyristor-controlled
circuit, or pulsed, as in a controlled rectiﬁer circuit, a computer, or power
to a UPS
...
Odd-order
harmonics are additive in the neutral conductions of the system, and
some of the pulsed currents do not cancel out in the neutral, even when
the three phases of the system are carefully balanced
...
Nonlinear load currents are non-sinusoidal,
and even when the source voltage is a clean sine wave, the nonlinear
loads will distort that voltage wave, making it non-sinusoidal
...

The factor harmonics cause resonance and high values often appear seemingly at random when certain combinations of equipment are run
...
f
...
A “tuning” inductor added in series
with the p
...
correcting capacitor will “tune out” the harmonics
...

Type I
Transients, sags, short powerfails, and other disturbances of less than
1/2 cycle are classiﬁed as Type I
...
The effect of these disturbances on computers is subject to debate;
only the most severe transient overvoltages are likely to disturb modernday electronic devices
...
Experience
indicates that there are few problems with most computers resulting from
AC power source overvoltages
...
The voltage
transient associated with the overvoltages may ﬁnd other paths, however,
to interact with data signals and cause data corruption
...
Momentary undervoltage (sags) resulting from power
system overloads or fault clearing are the most common causes of powerrelated electronic equipment system failures
...

Type III
Type III disturbances include voltage variations, brownouts, and
outages longer than two seconds
...

308

Efﬁcient Electrical Systems Design Handbook

MONITORING AND ANALYZING EQUIPMENT
Equipment for diagnosing power line disturbances can be purchased at prices ranging from only a few hundred to thousands of dollars,
and each type has its place
...
One or more comprehensive instruments might be kept in
the maintenance instrument inventory to provide qualitative information
on the speciﬁc nature of the problem after the lower-cost units have determined that a disturbance exists
...
On the other hand, manufacturers of UPS
systems might equally claim that installing a UPS system will eliminate
100 percent of power line disturbances
...
The ideal dedicated circuit will have, within
reason, the lowest possible impedance
...
To achieve this, the
source of the circuit should theoretically be as close to the building service entrance as possible
...
Thus, the
point of connection of the “dedicated circuit” is a judgment call
...

Shielded Isolation Transformers
Next to the dedicated circuit, the shielded isolation transformer is the

Power Line Disturbances

309

most popular power conditioner
...
Most power conditioner manufacturers agree this is among the
most important factors in providing a trouble-free power environment
...
Capacitive or electrostatic coupling is the only way
common-mode noise can be transmitted from primary to secondary
...

(See Figure 12-1
...
Types and Locations of Electrical Noise

The shield, which usually consists of a foil wrapping of conducting
non-magnetic material, conducts the electrostatic charge around the primary winding to ground, preventing it from coupling with the secondary, while providing greater than 300-to-1 common-mode noise reduction
...

Transverse mode transients or noise (unlike common-mode) do impress
a voltage across the primary windings
...
The shielded isolation transformer is often used in tandem
with voltage regulators, transient suppressors, and other devices and
power conditioners, because it offers excellent common-mode noise rejection and a clean ground
...
These devices utilize a ferroresonant circuit consisting of a capacitor in series with
a transformer coil
...
Because of the saturated core, secondary voltage remains fairly
constant, in spite of changes in primary voltage
...
One common use is to power the primary logic motherboard in an adjustable speed drive from a CVT, to help
isolate it from voltage variations
...
Therefore, high inrush loads such as
switching power supplies can produce transients and noise on the output
...

Transient Suppressors
Transverse-mode transient spikes are voltage spikes between line
conductors
...
As mentioned earlier, the
spike is generally the ﬁrst few half cycles of the leading edge of an oscillating overvoltage
...
This is the least understood and most
misapplied technique
...
Silicon avalanche diodes are used to achieve very
fast (5 nanosecond) clamping
...

Keep in mind that, in general, these devices only clip the spikes to
± several hundred volts peak-to-peak, which can still cause problems for
PCs and other electronic equipment
...
This can effectively convert a transverse mode problem to a commonmode problem
...

One very unusual and highly accurate “active tracking” ﬁlter senses the instantaneous sine wave voltage at any point in the cycle
...
This ﬁlter begins to limit the deviation from the true instantaneous
sine-wave voltage whenever the deviation becomes greater than ± 2 volts
...
Not only are spikes
clipped very effectively, but the trailing notches are also “ﬁlled in” by the
energy stored in the ﬁlter’s capacitance, which cannot be done by simple
clamping devices
...
)

Figure 12-2
...

An excellent discussion of transient suppressors and methods of
testing their effectiveness is detailed in reference [6]
...

Uninterruptible Power Supply
Where a high degree of voltage regulation and total isolation from
sags, dips, surges, and transients is required, an uninterruptible power
supply (UPS) may be used
...
As a minimum, the
UPS allows for orderly shutdown of computer equipment without risk of
equipment damage or memory loss
...
A surge suppressor or
other type of transient remover is necessary to prevent damage to their
solid-state components
...

Perhaps the biggest disadvantage of using UPS is their high impedance and the high voltage drops associated with that impedance
...
Sometimes it is necessary to size these systems for one or more multiples of normal operating current, to compensate for the resulting voltage drop
...

There are three major UPS versions
...
Direct current from the batteries is inverted to AC to power the UPS
changes utility power to direct current to charge a set of page computer
...
This
can cause a very short (4 to 16 ms) power dip to the load
...
(3) A reverse transfer
UPS offers additional security, because the computer load is transferred to
utility power if the UPS is temporarily overloaded or when a malfunction
occurs within the UPS itself
...
If the load
distorts the power supplied by the UPS, then the power fed to the loads
will not be truly “clean
...

However, many manufacturers add a disclaimer, such as “based on linear
loads” or “for reactive and inductive loads
...
Before purchasing any UPS, make certain that it is capable of supplying the actual types
of nonlinear loads to be connected
...
This approach was recently
used effectively when applied to a system of HVAC fans in a large indus-

Power Line Disturbances

313

trial building7,8
...
9
Grounding
No discussion on PLD is complete without giving consideration to
power system and instrumentation grounding requirements
...
The simplest task served by a system ground is the establishment of
an electrical potential reference
...

The individual instruments and computer components usually have
all exposed metal parts connected to the power supply ground
...
On a less spectacular scale, leakage currents
may produce potential differences of many millivolts between the cases of
instruments within the same room, causing errors in the proper operation
of the devices
...
10,11,12
Conclusion
The intent of this chapter has been to establish that the selection and
application of power conditioning equipment is a complex issue with no
simple solution
...
They disagree on the nature of the problem, and they disagree
as to which technologies are best for solving the problem
...

It is also important to understand the consequences and the cost of
the downtime, unscheduled outages, and equipment damage
...

Providing just the right level of protection to each PLD application is
the opportunity, and as pointed out at the beginning of this chapter, that is
your challenge
...
Basic Measuring Instruments 402 Lincoln Center Drive Foster City, CA 94404-1161
2
...
Nash, Jr
...
Wells, “Power Systems Disturbances and
Considerations For Power Conditioning,” IEEE Industrial & Commercial Power
System Technical Conference Paper
...
Arthur Freund, “Nonlinear Loads Mean Trouble,: EC&M, Pages 83-90
...
Arthur Freund, “Double The Neutral and Derate The Transformer—Or Else!”
EC&M, Pages 81-85
...
Arthur Freund, “Protecting Computers from Transients,” EC&M, pages 65-70
6
...
, 260 Fordham
Road, Wilmington, Mass
...
W
...
Stebbins, “A User’s Perspective On The Application Of Adjustable Speed
Drives and Microprocessor Control for HVAC Savings,” IEEE Textile Industry
Technical Conference Paper
...
Southern Industrial Controls, 10901 Downs Road, P
...
Box 410328, Charlotte, NC
28241-0328
9
...
446-1987
...
IEEE Recommended Practice For Grounding of Industrial and Commercial Power
Systems (IEEE Green Book) ANSE/IEEE Std
...

11
...
141-1986
...
Guidelines On Electrical Power For ADP Installations, Chapter 3, Federal Information
Processing Standards Publication, (PIPS PUB 94), U
...
Department of Commerce,
National Bureau of Standards
...
In addition, centrifugal chillers are a prime candidate
...

VARIABLE SPEED DRIVES
There are several variable speed drive systems that are available that
have been used for control of fan or pump speed
...

The unique advantage of the adjustable frequency drive is that the
standard AC motors may be used
...

This chapter will highlight AC variable frequency drive applications
...
Its speed depends
on the number of poles provided in the stator, assuming that the voltage
and frequency of the supply to the motor remain constant
...

The stator or primary winding can be connected to change the number
of poles
...
This method can give speciﬁc alter315

316

Efﬁcient Electrical Systems Design Handbook

nate speeds but not gradual speed changes
...
However, torque is proportional
to the square of the voltage, so reducing the line voltage rapidly reduces
the available torque and will soon cause the motor to stall
...

An excellent way to vary the speed of a squirrel-cage induction motor is to vary the frequency of the applied voltage
...
Adjustable frequency controls perform this function
...

For a 60-Hz motor, increasing the supply frequency above 60 Hz
will cause the motor to be loaded in excess of its rating, which must not
be done except for brief periods
...
As the
frequency is reduced, the voltage should also be reduced, to maintain a
constant torque
...
These and other modiﬁcations can be
obtained by varying the ratio of voltage to frequency as required
...

The speed of an AC induction motor can be changed over a very
wide range, from perhaps 10% to 20% of 60-Hz-rated speed up to several
times rated speed
...
At higher
speeds, care must be taken not to exceed the hp rating of the motor
...

At low speeds, roughly 20% of rated speed or less, especially if the motor is fan-cooled, care must be taken not to exceed the permitted motor
temperature rise
...

Capability, versatility and ﬂexibility of the AC induction motor are
matters of fact
...
These include type of application, enclosure, mountings,
coupling, bearings, insulation, temperature ratings, initial costs, operating
cost, energy rating, and starting and control requirements
...

2
...

Ability to adjust the frequency according to the desired output
speed
...

Ability to supply a rated current on a continuous basis at any frequency
...
The DC link ﬁlter the ripple at the output of the rectiﬁer, and the
combination of the controlled rectiﬁer and ﬁlter provides a variable DC
voltage to the inverter
...
An inverter belongs to the voltage source
...

Because of a low internal impedance, the terminal voltage of a voltage source inverter remains substantially constant with variations in load
...

Because of a large internal impedance, the terminal voltage of a current

Figure 13-1
...
Karmous, G
...

Efﬁcient Electrical Systems Design Handbook

318

source inverter changes substantially with a change in load
...
This voltage-to-frequency relationship
is referred to as volts per hertz so V/Hz is derived by dividing voltage by
frequency
...
66 V/Hz

(Formula 13-1)

For proper operation and full available motor torque, this ratio must be
maintained over the entire operating sped range of the system
...

230 VAC/30 Hz = 7
...
It consists of six self-commutation switches S1 to S6
with the anti parallel diodes D1 to D6
...
They may be realized using power transistors, GTOs, MOSFETS, or inverter grade thyristors with forced commutation circuits
...
A
snubber is required for each switch-diode pair
...
The
inverter may be operated as a square-wave inverter or as a pulse-width
modulated (PWM) inverter
...
With the square-wave
inverter operation, each inverter switch is on for 180°, and a total of three
switches are on at any instant of time
...

Voltage harmonics in the inverter output decrease as V1/h with h =
5, 6, 11, 13, etc
...
Because of substantial magnitudes of low-order harmonics, these
currents result in large torque ripple, which can produce troublesome
speed ripple at low operating speeds
...
3-φ Voltage Source Inverter

320

Efﬁcient Electrical Systems Design Handbook

PWM-VSI Drives
Figure 13-3 shows the schematic of a pulse-width-modulated PWMVSI drive
...
Therefore,
at the input, an uncontrolled diode bridge rectiﬁer is generally used
...
Therefore, a high switching
frequency results in an essentially sinusoidal current in the motor
...
Therefore, a small
value of capacitance sufﬁces in PWM inverters, but this capacitor must be
able to carry the ripple current
...

Figure 13-3
...
They control a motor’s speed electronically rather than
mechanically
...

In effect, the VFD sizes the motor to the load
...
Typical Power Consumption of Various Control Systems
Reprinted by Permission: Energy Engineering, Vol
...
3: “Proﬁt Improvement with Variable Frequency Drives,” Scott A Moses*, Wayne C
...
D
...
E
...
Wong,
Mark R
...

*This material is partially based upon work supported under a National Science Foundation
Graduate Fellowship
...

322

Efﬁcient Electrical Systems Design Handbook

is determined by its frequency, although a constant ratio of voltage to frequency must be maintained for the motor to produce full torque
...

Design Features
Sizing
A centrifugal fan or pump motor is sized to meet maximum load,
but usually this load occurs only a few hours a year
...

During off-peak periods, the load ﬂuctuates, and either’ dampers or
throttling valves control the ﬂow
...
However, the amount of energy wasted is substantial, since the
power requirement of a centrifugal fan or pump varies with the cube of
the speed, while the ﬂow varies directly with the speed
...
For example, reducing
fan speed 20 percent reduces air ﬂow 20 percent, but the power consumed
is reduced by nearly 50 percent
...
Originally, all air handlers were one-speed, constant volume units
...
Often, constant volume systems have been replaced with more efﬁcient Variable Air
Volume (VAV) systems
...
Both of these methods reduce the fan input power
...

Pumps
Similarly, pumping systems must be designed for maximum needed
ﬂow rates
...
Sometimes, extra ﬂows are delivered to the use point at
design volume regardless of need
...
The VFD
then controls the speed of the motor to deliver a constant pressure, rather
than a constant volume
...

Other savings include maintenance savings and reduced downtime
...
The
VFD will require no routine maintenance
...

Energy savings will be primarily determined by the load proﬁle for
the process
...
As noted earlier,
constant volume pumping or air-blowing systems are excellent candidates
when the actual load varies but the motor is run at full speed
...

Secondary considerations which will improve the attractiveness of a
VFD are: long operating hours, higher energy costs for electrical consumption, and a medium-size motor
...
It usually

Figure 13-5
...
Medium-size
VFDs tend to be most economical
...

Candidate Applications
Any fan or centrifugal pumping system with a varying load makes a
good candidate
...
Conversion from a constant volume, variable
temperature system to VFD control with constant temperature is especially attractive
...
A fan in a typical VAV
system runs at 80 percent speed or less 90-95 percent of the time,
which meets the widely-varying, low load requirement
...
)
Cooling tower fans
...

Mixers, conveyors, packaging and bottling machinery, dryers, crushers, grinders, and extenders
...
If the system peak and the period of low motor loading coincide,
demand savings should be added to the total annual dollar savings
...

Variable Speed Drives

325

Table 13-1
...
20
0
...
40
0
...
60
0
...
80
0
...
00

—•—
—•—
—•—
—•—
—•—
—•—
—•—
—•—
—•—

0
...
11
0
...
20
0
...
43
0
...
85
1
...
00
0
...
16
0
...
23
0
...
09
0
...
01

——
——
——
——
——
——
——
——
——

——
——
——
——
——
——
——
——
——

————————————————————————————————

————————————————————————————————
Total Annual Electricity Savings
...
$________

Column 2: Obtain the values from Table 13-2
Column 4: Source: Graham Co
...
The values in Table 13-1 are for a standard
duty cycle and should be used unless a typical duty for’ the entire year has been determined
...

Simply plug the new fractions into Column 4
...
7457)(hp)(hrs)(Column 2 - Column
3)(Column 4) where
Hp = Rated Motor Size, hp
Hrs = Hours of Operation, hrs/yr
Column 6: For each Load Ratio, calculate Dollar Savings = (Column 5)(COE)
where
COE = Cost of Electricity, $/kWh

————————————————————————————————
Table 13-2
...
20
0
...
40
0
...
60
0
...
80
0
...
00

1
...
10
1
...
10
1
...
10
1
...
10
1
...
64
0
...
82
0
...
97
1
...
11
1
...
22

0
...
67
0
...
72
0
...
80
0
...
99
1
...
04
0
...
16
0
...
39
0
...
71
0
...
12

————————————————————————————————

————————————————————————————————
*These ratios are speciﬁcally applicable to single zone, constant volume systems
...
Since the voltage will
not affect the annual savings, each feasible conﬁguration will be considered and the least expensive one selected
...

460V line voltage, 460V VFD, 460V existing motor
2
...

230V line voltage, 460V VFD, 230/460V dual-voltage motor, transformer
4
...

230V line voltage, 460V VFD, 460V new motor, transformer
Table 13-3 will assist in selecting the best conﬁguration option that is
compatible with your application
...
This method is a rough approximation,
since it neglects the time value of money
...

Net Present Value Method
In addition to calculating a simple payback, the net present value

Figure 13-6
...
Scenario Selection Matrix

————————————————————————————————
Available Line
Voltage Only

230V Only

230V and
460V

460V

————————————————————————————————
Motor Voltage

230V

230V/460V

230V

230V/460V

230V

230V/460V

Best Scenario

4

3

2 or
4

1

1

1

————————————————————————————————
————————————————————————————————
(NPV) should be obtained in the following steps:
(1) You should determine the annual savings and the installation cost of
a VFD in the above analysis
...
A good choice would be 4 years
...

(3) Predict the interest rate over the next N years
...

(4) Determine the present worth factor from a set of interest tables or
use the formula below:
(1 + i)N – 1
Present Worth Factor = ———————
(i)(1 + I)N
where
i = the decimal effective interest rate per period, such as 12 percent
per year, which would be 0
...

(5)

Compute the net present value (NPV) as follows:
NPV = (total annual savings) (present worth factor) – (Investment
Cost)
...

Decision Criteria
If the NPV is positive, the investment will result in a net gain over
the period of N years
...
If the NPV is nega-

328

Efﬁcient Electrical Systems Design Handbook

tive, it is not an attractive investment
...
They do not include maintenance savings (such as the elimination of inlet vane or outlet damper
maintenance), electrical demand savings, or savings from reduced downtime of the new system
...
Also, the
salvage value of the equipment has been neglected
...
If a VFD merits further consideration, the
application should be evaluated by a qualiﬁed consultant
...

An Ofﬁce Building
An ofﬁce building in Oklahoma has two air-handling units
...
It is a 440V unit
...
The present motor is 230V, but both 230V and
440V line voltages are available
...
16/kWh
...

Columns 5 and 6 are calculated using the previous formulas
...

Determination of Installation Cost
Using Table 13-3, the least expensive conﬁguration is determined for
the large air handler, which will be Scenario 1
...

VFD on Dust Collectors
A stainless steel foundry in Milwaukee, WI, has two cyclone dust
collectors, both of which have many pieces of equipment with varying
loads connected to them
...
The other, a 50 hp cyclone unit, has 15 pieces of equipment

Variable Speed Drives

329

Table 13-4
...
20
0
...
40
0
...
60
0
...
80
0
...
00

0
...
67
0
...
72
0
...
80
0
...
99
1
...
09
0
...
14
0
...
29
0
...
62
0
...
16

0
...
05
0
...
23
0
...
20
0
...
03
0
...
108,235 kWh

Table 13-5
...
20
0
...
40
0
...
60
0
...
80
0
...
00

1
...
10
1
...
10
1
...
10
1
...
10
1
...
09
0
...
14
0
...
29
0
...
62
0
...
16

0
...
05
0
...
23
0
...
20
0
...
03
0
...
46,562 kWh

————————————————————————————————
connected to it
...

The cyclone systems are set up so that when a piece of equipment
is shut off, a damper closes on that particular branch of the cyclone ducting
...
In
the following example the typical VAV system duty cycle is applied, with
electricity costs of $0
...

Efﬁcient Electrical Systems Design Handbook

330

Calculation of Annual Savings
The values in Column 2 of Tables 13-6 and 7 are obtained from Table
13-2 for inlet vanes
...

The total savings for both investments are $12,031 and 374,809 kWh
annually
...
For the 100 hp cyclone,
the installation cost is determined to be $9,572
...
The total investment cost will be $15,235
...

Simple Payback = ($15,235)/($12,031/yr) = 1
...
0373) – ($15,235) = $21,306
Since the NPV is positive, this is a very good investment
...
That requirement may
affect the economics of the project
...
Annual Savings for 100 hp Dust Collector

————————————————————————————————
1
Load
Ratio

2
Power Input
Ratio (Old)

3
Power Input
Ratio (VFD)

4
Duty Cycle kWh
Fraction

5
kWh
Saved

6
Dollar
Savings

0
...
30
0
...
50
0
...
70
0
...
90
1
...
57
0
...
71
0
...
75
0
...
88
0
...
20

0
...
11
0
...
20
0
...
43
0
...
85
1
...
00
0
...
16
0
...
23
0
...
09
0
...
01

0
15666
51026
66916
59195
41403
13092
2350
224

0
503
1638
2148
1900
1329
420
75
7

————————————————————————————————

————————————————————————————————
Total Annual Electricity Savings
...
$8,020/yr

Variable Speed Drives

331

Table 13-7
...
20
0
...
40
0
...
60
0
...
80
0
...
00

0
...
67
0
...
72
0
...
80
0
...
99
1
...
09
0
...
14
0
...
29
0
...
62
0
...
16

0
...
05
0
...
23
0
...
20
0
...
03
0
...
124,937 kWh
Total Annual Dollar Savings
...

The following summarizes the advantages of VFDs
...
For example, consider an air-handling unit operating at 50
percent of full load
...

Compensation for Oversized Designs
A VFD will effectively size the motor to the load, regardless of motor
horsepower
...

High Power Factor
The power factor of a VFD is typically about 0
...

Some utilities penalize heavily for low power factors, leading to sig-

332

Efﬁcient Electrical Systems Design Handbook

niﬁcant dollar savings when the power factor is improved
...
Installation takes only a few hours
...

Designed to Work with Standard AC Motors
Interface Easily with Computers
A VFD can be connected easily to a computer energy management
system
...

Have Soft Starting Capability
When a normal motor is started, the surge of electric current that
moves the motor out of its stationary position is about six times the ordinary current
...
However, the acceleration time on a VFD
can be adjusted from instantaneous to several minutes to reduce the
stress
...
The reduced current and voltage drop associated
with soft starting will reduce motor heating
...

Re-acceleration and Rotating Motor Restart Capability
If the power should be brieﬂy interrupted, the VFD will resume operation immediately, whereas ﬁxed speed devices would not
...

Not Just an Energy-saving Device
VFDs are often used in speed control applications because of their
accuracy and their ability to control a number of synchronized motors
...

Variable Speed Drives

333

AC VARIABLE SPEED DRIVES/INVERTERS EXAMPLES*

Figure 13-7
...
(Used with permission of AutomationDirect)

GSI Series Mini-drives (Automation Direct)
The GSI series of AC drives have V/Hz control with advanced application features
...
Standard GS1 features include one analog input, four
programmable digital inputs, and one programmable normally open relay output
...
The drive
can be conﬁgured using the built-in digital keypad or the standard
RS485 serial communications port
...
Each GS2 AC drive features one
analog and six programmable digital inputs, as well as one analog and
two programmable relay outputs
...

The DURApulse series of AC drives offers all of the features of our
*From Automation Direct 2008 Catalog
...
The DURApulse drives also offer sensorless vector control, with the option of encoder feedback for
enhanced speed control
...
k
...
HIM or human interface module) is designed with defaults for North American customers and allows
you to conﬁgure the drive, set the speed, start and stop the drive, and
monitor critical parameters for your application
...
The DURApulse series offers three
analog inputs, eleven digital inputs, and one SPDT relay output
...
IGBT technology
•
175% starting torque
•
150% rated current for one minute
•
Internal dynamic braking circuit for models under 20 Hp
•
Automatic torque and slip compensation
•
Programmable jog speed
•
Removable smart keypad with parameter upload/download
•
HIM keypad with memory to store up to four programs of any DURApulse drive Three analog inputs and one analog output
•
Eleven digital inputs
•
Three digital and one SPDT relay output
•
One analog output
•
RS485 MODBUS communications
•
Ethernet communication optional
•
UL/CE listed
•
Optional software package with full programmability, trending, and
application setup
Typical Applications of DURApulse AC Drives
Some of the typical applications for which DURApulse AC drives
are used include: conveyors, fans, pumps, compressors, HVAC, material
handling, mixing shop tools, extruding, and grinding
...

Doll, Thomas R
...

Fugill, Richard W
...
“What You Should Know About Adjustable-Speed
Drives,” Electrical Construction and Maintenance
...
G
...

Automation Direct 2008 Catalog
...
”

Chapter 14

Field Measurements and
Determination of
Electric Motor Efﬁciency*
Conservation of electricity in electric motors and the systems they
drive has been a subject of increasing concern recently
...
A number of papers have appeared
about the efﬁciency of electric motors and the procedure for selection of
an appropriate motor to perform a particular task
...
2,3
Almost all of these papers address the issue of new motors and are
useful when the decision to purchase a new motor has already been made
...
Some of these motors may not be performing their task
efﬁciently, and a cost effective alternative toward better performance may
exist
...
For example, there may be an inherently inefﬁcient motor, an improper match to load, a poor rewind job (if rewound), or voltage imbalance
...
This paper reports work towards several methods to evaluate operating conditions:
•

Determining a suitable procedure for ﬁeld measurements, including a package of instrumentation and data acquisition hardware to
facilitate large-scale ﬁeld testing of the motors

*Reprinted with special permission; K
...
Lobodovsky, R
...
Gupta, PG&E
Company, Energy Engineering, Vol
...
3
...
The overall motivation for promoting this program,
along with the explanation of the speciﬁc objectives and applications, is
to achieve economically optimal efﬁciency that is beneﬁcial for all parties
involved in the program, including:
•
•
•

The plant operators—obtaining more competitive production costs;*
The utility—avoiding new capacity by reducing wasteful usage;
The state—continuing lower electricity rates and enhancing industrial productivity
...
More
speciﬁcally, the objectives of the program can be divided into three areas
of interest:
•
•
•

Motor performance from ﬁeld measurements for determination of
applicable alternatives
...

Long-term database development for planning utility conservation
programs
...
However, the insights and experience are equally applicable in nonindustrial applications
...
Objectives and Applications of Field Motor Testing Program

rated service duty range
...
For example, if the motor is found to be underloaded, downsizing and NOLA devices can be considered, in addition to

340

Efﬁcient Electrical Systems Design Handbook

the replacement by a new more efﬁcient motor
...
The measurements required for this method are load and no
load voltages, amperes, power factor (or power), shaft RPM and the stator
resistance
...
But, this is seldom
found to be true in ﬁeld conditions
...
This is especially true of the no load measurements, which require uncoupling the motor
...
This further permits calculation of relevant
motor parameters to allow a complete characterization of the motor performance at any load point
...
In Table 14-1, this is shown under 2
...
1
...

On the other hand, partial measurements in many instances can provide some clues about the motor
...
Thus, a second objective, shown under 2
...
2 in Table 14-1, is to determine the conditions
where even the partial ﬁeld measurements can provide sufﬁcient information for either a ﬁnal decision (to replace, or not replace, or retroﬁt) or an
indication as to whether a full test is warranted
...
1 in Table
14-1
...
The electricity prices over time are
taken from the utility, state or operator’s own projections
...
The economics of alternatives are calculated in terms of simple
payback and a complete internal rate of return (accounting for taxes, depreciation and any tax or other incentives provided to a technology option)
...

This information will be used to evaluate the cost-effectiveness of
any programs initiated by the utility company or public agencies
...

The ﬁnal objectives consist of developing a long-term database of
ﬁeld test results, manufacturers’/rewinders’ data, and the follow-up results of the actions by the plant operators
...
It is our hope that with sufﬁcient ﬁeld experience in conjunction with the cooperation from the motor industry (both manufacturers and the repair/rewind industry), general trends and rules of thumb
can be developed
...
This goal is cited in Table 14-1 at 2
...
2
...
A U
...
Department of Energy study
estimates the motor power consumption to be in the order of 80 percent
of the industrial and commercial sector’s electricity demand
...

Test Procedures and Evaluation Programs
Test Procedure
The procedure adapted for motor testing was in accordance with the
IEEE Standard 112-1978, a combination of methods E and F as outlined
in the standard
...
1 This involves
the following tests:
•
No load test
...
The voltage, current, and power readings are to be
taken under the no load condition
...
The stator resistance of the motor is to be calculated

342

•

Efﬁcient Electrical Systems Design Handbook

by measuring the line-to-line resistance
...

Load test
...
Motor speed is also to be measured under the actual load condition
...
Instead, the ratio of the stator
reactance to the rotor reactance is assumed according to the NEMA
design of the motor
...

(2) The stator temperature rise is assumed on the basis of the insulation
class, as outlined in the IEEE test procedure
...
In accordance with ANSI C50
...
2 percent
of the rated output under full load conditions
...

(4) The reduced voltage test under no load condition is not performed
...
This result is a small decrease in the calculated rotor
resistance loss
...

(5) All electrical measurements are made at the motor starter terminals
...

Speed is measured under no load conditions to ensure that the motor is indeed unloaded
...
Supply voltage values and the line frequency are
monitored for any signiﬁcant voltage imbalance and departure from 60
Hz frequency
...

Instrumentation
After initial experimentation with various instruments, a DRANETZ
808 was chosen for voltage, current, and power measurements, whereas
shaft rpms were measured with a digital strobe-scope
...

The Computer Program
A computer program was written to process the information collected from the tests
...
Not only does it provide us with complete information about
the motor behavior under the existing operating conditions, but it also
predicts the motor behavior under different operating conditions (voltage,
and load point, etc
...

The memory and processing time requirements of the program are
reasonably small
...
1
Evaluation of Financial Attractiveness
Two basic parameters are used to evaluate the ﬁnancial attractiveness of the alternatives—simple payback and internal rate of return
...

Energy savings $/yr
(at a particular load)

=Motor size in HP ×
...

An after tax, discounted cash ﬂow analysis was used to calculate
the IRR
...

Such an analysis accounts for depreciation, investment tax credit, electricity price escalation rates, tax rates, and rewind costs
...

Field Experience
Before presenting the results, some general remarks about our experiences are in order
...
The steps involved not only the testing of instrumentation, where
some ideas for improvements have emerged and are being implemented for
future testing, but also the cooperation of the plant operators and the testing
personnel
...

After some experimentation with different instrument conﬁgurations, it was decided that the goal should be a package that provides
simultaneous hard copies of readings, hence minimizing errors due to
changes in loads
...

The DC resistance readings were taken with a separate multimeter
...

In the long run, the DC resistance readings and signals from the rpm
measuring device will be inputted and recorded along with the electrical
readings
...
This will add the ability to establish the efﬁciency of the motor under time-varying conditions
...

Site Tests
The ﬁrst plan of the program involved ﬁeld measurements at four
industrial plants in Northern California
...

The four plants where on-site motor tests were conducted varied
widely in every respect
...
The functions and states

Field Measurements and Determination of Electric Motor Efﬁciency

345

of the motor were equally divergent
...
In several instances this involved minor interference with the
process, and the no load tests had to be rushed because of the extreme limitation on the time that the motor could be kept decoupled from the equipment
...
One plant ran one shift only, the no-load tests
were performed after the shift was out, whereas the no-load testing in
the other plant had to be scheduled when the process line came down for
biweekly maintenance
...
The rest were completed when the plant was down for a
major revamping operation
...
Of course, if
the tests are carried out in close cooperation with (or by) the plant operators, the scheduling and other coordination logistics are reduced
...
Generally, it took two maintenance personnel from the plant to uncouple and put the motors back together
...
Most of the
motors selected for the present set of tests were belt driven
...
The data on costs and nominal efﬁciencies
of the replacement motor were based on published ﬁgures from a leading
motor manufacturer
...
The electricity price was assumed to be 7
...
For purposes of calculating the internal rate of return (IRR), a tax life of 10 years,
with a straight line depreciation and 10 percent investment tax credit were
assumed
...
All
recommendations are based on a 20 percent minimum IRR
...
On an average, they are operating at 60 percent of the rated load
...
However, downsizing may not
be a feasible option in applications where the process could require extra
power under unusual circumstances
...
A change in frame size, in some instances, can impose additional
costs
...
The
possibility of the applicability of a NOLA-type power factor controller on
some of the heavily underloaded motors is being investigated
...
The actual rate of return on the investment will probably be higher, due to reduced losses in power supply
cables and transformers, since efﬁcient motors draw less current
...
However,
more efﬁcient motors usually operate at a slightly higher speed, resulting in lower rotor resistance losses
...
This fact has been generally neglected and in our opinion requires serious consideration when
evaluating higher efﬁciency (lower slip) motors
...
Another ﬁve, though properly sized, would
be candidates for replacement with favorable economics
...
of Indianapolis, IN, actually designed the instrument for motor testing and used the software
PG&E developed for them
...

Conclusion
Based on the experience and results to date, the broad conclusion
emerges that the ﬁeld testing of motors is likely to be quite useful
...
In addition to the motor testing, it was recommended that additional measurements on end-use equipment (like
pumps) be made so that the total system performance and efﬁciency can
be estimated
...

Finally, a complete instrumentation package that includes a simultaneous
shaft rpm measurement and recording facility will make this program

Efﬁcient Electrical Systems Design Handbook

348

more effective and convenient for large scale applications
...
Paciﬁc Gas
& Electric: East Bay Division, D
...
Blessent, B
...
Purcell; and
Department of Engineering Research, R
...
Renouf
...

2
...

4
...

6
...

8
...
, et al
...
“Justiﬁcation for energy efﬁcient motors,” Proceedings of Third Annual Industrial Energy Conservation Technology Conference, Houston, Texas
...
“Motor Efﬁciency,” IEEE Transactions on Industry Applications, 1A15, (5)
...
“The design and application of induction motors for efﬁcient energy
utilization,” IEEE Industry Applications Society, Annual
...
“Motor efﬁciency can mean big savings,” Electrical World
...

“American National Standard for Polyphase Induction Motors for Power Generating
Stations,” ANSI, C 50
...

“Classiﬁcation and Evaluation of Electric Motors and Pumps,” DOE/TIC-11339
...
Since
motors account for over 76 percent of the power used by industry, they
have always had an impact on operating costs
...
Many answers can be found, ranging
from the observation that “a rewound motor is never as efﬁcient as the

Figure 15-1
...
Other Future Costs
*This chapter was written by the late David Montgomery, General Electric Co
...

349

Efﬁcient Electrical Systems Design Handbook

350

original” to “a high quality rewound motor can have a higher efﬁciency
than the original
...

Motor Losses and Proﬁts
Although motors are more efﬁcient than any of the equipment they
drive, their operating cost is of vital importance, because they account
for a signiﬁcant amount of the power used by industry
...
12/kWh power rates and 89
...
Useful work represents $39,210 of this total and motor losses, $4,730
...

Increased energy costs have highlighted the problem of motor
damage repair
...
There was little concern if
the motor drew more current and the watt-hour meter ran faster
...
The problem of low quality rewinds
can no longer be ignored
...
12/kWh, 89% Efﬁciency
Figure 15-2
...
It is not a wise business decision to attempt to save money with
a low cost, low quality motor rewind
...
The
largest is stator and rotor I2R losses, which are almost 50 percent of total
losses for a 50 hp drip-proof 3,600 rpm motor at full load
...

Core Loss
1030 Watts

Friction &
Windage
750 Watts

Stray Load
620 Watts

Stator & Rotor I2R
2100 Watts

Figure 15-3
...
Core loss is the sum of the eddy current and
hysteresis loss associated with energizing the motor’s magnetic circuit
...

Stray load losses are a result of leakage (harmonic) ﬂux induced
by load current
...
The losses
associated with a stator winding are primarily I2R losses caused by current
ﬂowing through a resistance, which in this case is the stator winding
...

Total motor losses vary with load as shown in Figure 15-4
...
As indicated, core loss and friction and
windage losses do not vary with load
...
Motor Losses vs
...

This is signiﬁcant because most motors do not operate at nameplate or 100
percent load
...
For
duty cycle applications, they can operate at all loads, including extended
periods of time at no load
...

Stator Losses
If a repair facility does not have the correct wire size in stock and uses
a smaller diameter wire for the rewind, the stator I2R losses will increase
...
This attempt to save labor can be very
costly to the motor user in motor efﬁciency, operating costs, and reliable
operation
...
However, this change from the original design will
increase the magnetic ﬁeld
...
With a high-ﬂux density design such as
a T-frame motor, the increase in core losses that result from a reduction in
the number of turns will not be offset and efﬁciency will be reduced
...
For most integral hp motors, the peak
efﬁciency occurs below full load, and most motors are used on loads that
are less than the nameplate rating
...

Changing the number of turns must further be viewed with caution
because it will also increase starting current and starting and maximum
torque
...

Windage and Friction Losses
Losses not normally affected by a rewind are windage and friction
losses
...

Rotor Losses
During a rewind, if the stator turns are reduced, the ﬂux density
increases, which reduces the rotor I2R losses and reduces the motor power
factor, an undesirable result
...
If the utility
charges a power factor penalty and/or a demand charge based on kVA
usage, there will be an additional increase in the power bill
...

Stray Load Losses
Stray load losses include additional fundamental and high frequency
losses in the iron, the strand and circulating current losses in the stator
winding, and harmonic losses in the rotor conductors under load
...
Damaged stator or
rotor cores and frames or end shields that affect air gap symmetry can
increase stray load losses
...

354

Efﬁcient Electrical Systems Design Handbook

Core Losses
If in repairing a motor, the rotor must be turned, the air gap will
increase
...
If an end-shield repair
or replacement is required, and the rotor and stator are longitudinally
misaligned, there will be a reduced air gap area across which power can
be transmitted, increasing the I2R losses
...
These losses can be decreased in design
and manufacture by making the core laminations thinner and by having
adequate insulation between the laminations
...

The greatest risk of core damage occurs during the stripping of the
old winding in the repair process
...
This heat will break down the insulation between laminations,
resulting in dramatically increased eddy current losses
...

Costly Low Quality Rewinds
Motor rewinds can have hidden costs
...
The additional losses associated with
the lower efﬁciency can cause premature failures, resulting in additional
maintenance cost, and lost production due to increased motor downtime
...
Four realistic possibilities where
core losses have increases of 50, 100, 150 and 200 percent are shown in
Figure 15-5
...
That
is equivalent to adding a good-sized space heater inside the motor
...
If the motor
operates continuously, as many motors do, with electricity at 12¢/kWh,
the annual increase in operating cost would be more than $2,000
...

Assume that a rewind facility rewinds a 50 hp motor at a 20 percent
discount from the typical price, but in the process this increases the core
loss by 100 percent
...

Testing Rewinds to Avoid Motor Efﬁciency Degradation

355

—————————————————————————————
Annual Operating Cost
Increase

Core Loss Increase

—————————
50%
100
150
200

—————————

515 Watts
$542
1030
1,080
1545
1,626
2060
2,168
50 hp 3600 rpm Dripproof Continuous Duty

—————————————————————————————
Figure 15-5
...

After the motor was rewound, it failed in a very short period of time
...

While this could have been the case, another reason for premature failure
could be that the stator core was damaged during the stripping process
...
Total: 355%

————————————————————————————————
Figure 15-6
...
With an additional 1,000
watts, there would be a corresponding 14°C temperature rise, as shown in
Figure 15-7
...
As shown in Figure 15-7, one of the major causes of motor failure is
insulation breakdown
...
Rise
Increase

————

Approximate
Insulation Life

——————

515 Watts
7°C
1030
14
1545
21
2060
29
50 hp 3600 rpm Dripproof Continuous Duty

62%
38
24
14

—————————————————————————————
Figure 15-7
...
As bearing
temperature increases, the grease life drops rapidly
...
This means the motor user will have to
regrease more often or the motor will experience bearing failure, another
major cause for motor downtime
...
These in-and-out expenses can be considerable, because
when a motor fails it is necessary to disconnect the motor from the driven

Figure 15-8
...
Rise
Increase

————

Approximate
Grease Life

——————

515 Watts
7°C
1030
14
1545
21
2060
29
50 hp 3600 rpm Dripproof Continuous Duty

85%
69
58
46

—————————————————————————————
Figure 15-9
...
When the repaired motor is
returned, it must again be reinstalled
...
Some companies assign a value
to downtime as costing tens of thousands of dollars per hour
...
Another way of
expressing this is to say that after rewind the motor’s losses will be 20
percent higher
...

———————————————————————————
Efﬁciency
Losses
89
...
5 kW
88
...
0
87
...
5
87
...
4
Rating: 50 hp 2600 rpm Dripproof

Increase
Base
0
...
0
0
...
Losses at Various Efﬁciencies

The only loss that can change is the core loss, if the motor is rewound
to the same winding wire size and conﬁguration and there is no change
in the rotor, bearings, grease, fan or other parts
...

Efﬁcient Electrical Systems Design Handbook

358

——————————————————————————————
Motor Rating—DP

50 hp
3600 rpm

100 hp
3600 rpm

50 hp
1800 rpm

Original Efﬁciency
Core Loss
Total Loss

89
...
1%
964 Watts
6398 Watts

90
...
Twenty Percent Average Increase in Total Losses

Although this type of increase can occur, it can also be avoided by
purchasing high quality rewinds
...

Verifying Quality
When a motor is rewound properly, the user gets a new winding, an
insulation system as good or better than the original, and new bearings
...

Even the best rewind, with bad stator core iron, is subject to failure
...
This is no longer true
...
The
tester is used to check each motor as it is received for repair for core loss
...
Losses in watts/lb can be compared
to predetermined standards
...
Motors that
would be too costly to operate or would fail prematurely can be identiﬁed
and replaced
...
An increase in the core loss can
be veriﬁed by using the core loss tester before and after repair to the iron
...
Because of the simplicity and speed of the core loss test, it is
now feasible to use this quality assurance tool on every motor
...
These estimates were based on
an assumed average 20 percent increase in core losses after rewind
...
This variance
ranged from 0 to 400 percent
...

If the test data are representative, they show original estimates of
hundreds of millions of dollars wasted by inefﬁciently rewound electric
motors to be low
...

According to the tests, this wasted energy would be 60 percent greater
than originally thought
...
An increase ranging from 0% to 9% was found on 21 to
39 percent of the motors tested
...
Tests showed that 8 to 10 percent of the motors had been
substantially damaged (those with over 100 percent in core loss), and
unless the damage was repaired they would be candidates for premature
failure
...

——————————————————————————————
% Increase
0-9%
10-50
51-100
101-400
Total

Motor hp Size
5-20 hp
25-80 hp
38%
39%
47
48
9
4
8
9

——

100%

——

100%

75-200 hp
21%
58
11
10

——

100%

——————————————————————————————
Figure 15-12
...
GE
test results over a one-year period show that core losses can be reduced to
the original level or to an acceptable value in 98 to 99 percent of the cases
...
The amount of time spent
repairing the iron on a small 10 hp motor can be excessive when compared
to the cost of a new motor, whereas with a larger motor it is frequently
possible to justify the cost of a major repair such as restacking the iron
...
There will be dramatic
reductions in core loss with a high quality rewind
...

Figure 15-13 shows an actual example of a motor with high core
loss
...
This reduction of 918 watts represents real savings to the motor
user
...
12/
kWh
...

—————————————————————
Initial Core Loss
Final Core Loss
Reduction

1809 Watts
891
——
918 Watts

—————————————————————

Figure 15-13
...

Alternative Test Methods
The core-loss tester reviewed earlier is not the only way to test the
quality of a motor’s stator core iron
...

Load Test
Although a load test can be used to verify a motor’s performance, it
has serious limitations when used to determine if there has been a change
in core loss during the rewind process
...
To be comparable, the load test must be performed on a
dynomometer in accordance with NEMA Test Standard MG1-12
...
This type of test
can take several hours, since it is necessary to wait until the temperature
rise of the motor levels off
...
This is particularly true if the core losses
are lumped together with other losses by measuring them only at full load
...
Therefore, it could not be used to screen for damaged
stators in failed motors
...
(1) stator I2R losses
at no load; (2) friction and windage losses; and (3) core losses including
both hysteresis and eddy current losses
...
The friction and windage losses
are determined by a more complicated process
...
The watts are
plotted vs
...
The no load losses at zero volts squared are
the friction and windage losses
...

Although the no load test can be used to determine a motor’s
core loss, it is time consuming and can only be used when a motor is in
operating condition
...
The test consists of running full load current
at a reduced voltage through a series of cable turns wrapped through
the stator and around one side until hot spots occur
...
This is not foolproof,
since the hands of many repairmen cannot detect a temperature difference
unless it is 15°F or greater
...

The greatest disadvantage is that it is too time consuming
...
The new core loss tester has detected many
bad stator cores that looked perfect and would not have been candidates
for the ring test
...

Although the ring test will not give a quantitative core loss
measurement, it could temporarily be an acceptable alternative when
used in conjunction with an infrared scanner, which will more accurately
detect hot spots
...
An analysis of GE’s test results shows
this has happened frequently
...
Unfortunately,
an increase in core loss is difﬁcult for the motor user to identify
...
Two of these would be higher full load current
and higher operating costs
...
A change in
voltage or load could easily account for a current change of this magnitude
...
The
corresponding increase in operating costs is easily clouded by the overall
increase in the user’s electric bill
...
Defective materials or poor workmanship will
probably be blamed for motor rewind failures that occur within the
warranty period
...
For a number of reasons,
a majority of motors only operate between 50 to 80 percent of their rating
for continuous duty applications and frequently below this on duty cycle
applications
...
Although the damaged core iron may not result in a
failure, it will increase operating cost unnecessarily
...
This has been true for core loss testing
...
They are insisting that their motors be tested for
core loss as part of the rewind process
...

Figure 15-14 shows that it is even more important to prevent any increase
in core losses on larger motors, because these losses represent such large
blocks of power
...
The
original testers were designed to handle the smaller hp random-wound
designs
...

Figure 15-14
...
High rewind quality can now be veriﬁed by the core loss
tester
...
Before a problem can be solved, it must ﬁrst be
recognized and understood
...

The speciﬁcation should also require the replacement winding to have the
same wire size and number of turns as the original winding
...
This can be very costly over a period of time
...

There are many ways to reduce motor rewind costs, but unfortunately
most are at the expense of quality in both operating cost and motor life
...

Chapter 16

Guidelines for Implementing
An Energy-efﬁcient
Motor Retroﬁt Program*
INTRODUCTION
Stanford has recently completed a group retroﬁt of 73 HVAC motors
with new energy-efﬁcient models
...
Detailed procedures
for testing motors are included
...
Initial trials indicate that the accuracy of the simpliﬁed method compares quite favorably to the complete
testing procedure
...
Perhaps best known for its close ties with the electronics industries of the adjacent “Silicon Valley” area, Stanford has also
developed highly acclaimed programs in areas such as computer science,
medicine, and business
...
Energy
management has been an important component of facilities design and
maintenance
...
Later, few opportunities for simple measures such as
delamping and lamp replacement remained
...
Most signiﬁcant of these projects were retroﬁts of
building mechanical and control systems
...
Wilke and T
...

365

366

Efﬁcient Electrical Systems Design Handbook

Then began a study of the feasibility of retroﬁtting motors serving
HVAC systems with new energy-efﬁcient models
...

Should motors be replaced before failure?

2
...

Will there be any adverse effect on the HVAC system?

After reviewing standard and high efﬁciency motor performance
data, along with current energy prices, we quickly saw that group replacement before failure was an attractive option
...
Since energy-efﬁcient motors are higher quality versions of
standard motors, no adverse affects on the HVAC system are involved
...

Though most businesses will not invest in projects with paybacks
greater than two or three years, Stanford (and most other similar institutions) looks more to the long term and accepts paybacks of ﬁve years or
even more, especially if there are other beneﬁts
...
However,
many cases had paybacks of less than two years; the average payback of
the whole project (73 motors) was three years
...

Carrying out motor retroﬁts by group replacement offers several advantages: easier coordination of payback analysis and installation, price
discounts with group orders, and the ability to develop a “composite payback
...
One disadvantage of waiting until failure to replace motors is that energy-efﬁcient motors are typically stocked in lesser
quantities and the right size might not be available
...

Using the Stanford project as an example, this chapter discusses how
to implement an energy-efﬁcient motors program
...

2
...

4
...

367

Review Motor Basics
Initial Survey
Field Testing
Payback Analysis and Vendor Selection
Installation and Follow-Up

A simpliﬁed yet accurate alternative to the full ﬁeld testing procedure is also presented
...

It is important for the energy manager to keep careful documentation
during each phase of the project
...
Fortunately, much of the analysis and recordkeeping for this type of project becomes easy when using a spreadsheet
package such as Excel
...

The ability to select the installations with the best payback is the key
to the whole program
...
The ﬁrst two items are relatively easy to set, but the last two are
more difﬁcult
...

This method has several problems
...
This is not
uncommon with older motors
...

Even when the nameplate efﬁciency is available, this value is usually not equal to the actual operating efﬁciency
...
Further error
can result from assuming that the motor is operating at rated load, since
the actual load factor directly affects energy consumption
...

Finally, the efﬁciency can be affected by deterioration in motor insulation
or other motor components over time
...
Fortunately for Stanford, Paciﬁc Gas & Electric Co
...
To use this computer program, a detailed test procedure had to be carried out for each motor site
...
The test procedure and program calculations are
described in more detail in a later section
...
In a typical three-phase AC motor, current passes
through the motor windings and creates a rotating magnetic ﬁeld
...
In HVAC applications, the shaft energy is used to drive a pump impeller or fan wheel to
move liquid or air
...
At a given frequency,
the number of poles determines the speed of the magnetic ﬁeld (known as
synchronous speed)
...
S
...
However,
when the motor is connected to the driven load, the actual shaft rpm is
less than the synchronous speed
...
The difference
between synchronous speed and shaft RPM is referred to as “slip
...
The efﬁciency of the motor is deﬁned
as:
Output Power
Efﬁciency = ————————
Input Power

(Formula 16-2)

Unfortunately, a complex procedure must be followed to make a precise
measurement of horsepower output
...

Guidelines for Implementing an Energy-efﬁcient Motor Retroﬁt Program

369

These motor losses occur in several places
...

No-load Losses
Windage and friction losses are due to bearing friction and mechanical losses in the rotor windings
...

Stator losses (or I2R losses) are resistive or ohmic losses that are a
function of the stator no-load input current and the stator resistance
...
Input current and stator resistance are measured under typical load and temperature conditions
...

Stray load losses result from “stray” current that circulates in the
magnetic steel and windings
...

Energy-efﬁcient motors are designed to reduce the above losses
...
These improvements reduce internal
electrical resistance, which in turn cuts down losses
...

INITIAL SURVEY
To convince management that a group replacement with energy-efﬁcient motors is a worthwhile investment, it is necessary to compile some
data on the existing stock of motors
...
While the difference in
efﬁciency between a standard and energy-efﬁcient motor increases with
decreasing motor size, the energy consumed also decreases with size; thus
the actual savings are relatively small
...
At Stanford, we limited our initial survey to motors in the 7
...
We also limited our survey to motors that ran at
least 2000 hours per year
...

Depending on how many motors a facility has, it might be better to narrow
this range even further, to perhaps between 15 and 30 hp
...
For each of these motors we noted location,
size, and service (fan or pump) and estimated the hours per year the motor
operated
...

Once the survey data are gathered, a preliminary analysis can be
made to get a rough idea of the potential costs and energy savings
...
To be conservative, one can
assume that the efﬁciency of existing motors is equal to standard catalog
(or nameplate) efﬁciency
...
Thus if the estimated payback is even close to acceptable, the energy manager should continue with a testing program, since he knows
that the paybacks will improve with better data
...
First, make special note of any motor that is under variable
loading
...
Therefore, the efﬁciency
and load factor testing must also be done at maximum load
...
” Taking readings at partial load might mistakenly suggest downsizing the motor
...
In this situation it is very unlikely that the additional expense for an
energy-efﬁcient motor can be justiﬁed
...
Worn belts and pulleys can reduce the applied load to the
motor, giving the impression of an underloaded motor
...
To avoid this problem, simply
replace worn belts or pulleys before testing
...

Another concern is motor frame size
...
Purchasing a new frame for

Guidelines for Implementing an Energy-efﬁcient Motor Retroﬁt Program

371

each motor can add signiﬁcantly to the cost of the project
...
For
most new motors we installed frame adapters that were much less costly
than an entire new frame
...
Make sure that the size of these components is correct for the new motor
...
If a larger motor is
being installed, it may even be necessary to replace the starter
...

Before beginning any testing, make sure that all the survey data
are as complete and well organized as possible
...
This original spreadsheet will serve as a master listing that can be added to and
manipulated through various stages of the project
...

FIELD TESTING
IEEE Standard Number 112 is the U
...
standard that deﬁnes efﬁciency testing procedures for polyphase induction motors
...
Other methods require more complex
testing that we decided was not necessary
...
This factor was built into the CEC/PG&E motor
efﬁciency computer program that we used to analyze the data
...
One set of readings is taken while
the motor is loaded, and one set is taken under no-load conditions
...
For each
condition, the following measurements are taken:

372

•
•
•
•
•

Efﬁcient Electrical Systems Design Handbook

Input current, voltage, and power
Stator winding resistance
Shaft speed (rpm)
Motor surface temperature
Ambient temperature

The recommended procedure for making these measurements is
outlined below:
Load Test
(Let motor run for one hour or more before test
...

De-energize motor at breaker or disconnect switch
...

Take stator winding resistance between each line pair
...

Hook-up power meter
...

Energize motor and allow to run until readings stabilize on power
meter
...

5
...

6
...

7
...

8
...

9
...

No-load Test
1
...

2
...

3
...

4
...

It is possible to reduce the amount of no-load testing required by
using a no-load database
...
The CEC/PG&E program offers a limited amount of no-load data, but these data were not
well matched to our existing stock of motors
...
After we had tested many motors
we were able to generate our own no-load data, which proved quite useful
...

Guidelines for Implementing an Energy-efﬁcient Motor Retroﬁt Program

373

Test Equipment
As outlined in the above procedure, a variety of measurements must
be made to complete the tests
...

Fortunately, our electric shop has an Esterline Angus power demand meter
...
There are a variety of similar meters on the market, with a range of capabilities and prices
...
The critical criterion in selecting a DMM is the capability of making accurate resistance measurements in the low (0-2 ohm)
range, since stator resistance lies in this range
...
The DMM was also used for
current, voltage, and temperature measurements
...

The remaining piece of equipment we used was a stroboscope to
measure shaft rpm
...

PAYBACK ANALYSIS AND VENDOR SELECTION
Payback Analysis
Once all of the test data were compiled and the load factor and efﬁciency calculated by the CEC/PG&E program, a detailed payback analysis was made
...

Annual kWh savings for each motor were calculated using the formula below:
Where:

A = (HP × L × H × (1/η1 – 1/η2) × C)
× (0
...
At this
stage we were also able to calculate what our rebate would be from the local utility (PG&E) rebate program
...

After the paybacks were all calculated, we were able to sort the
spreadsheet quickly in order of increasing or decreasing payback
...
All motors
that had an after-rebate payback of ﬁve years or less were then targeted for
retroﬁt
In compiling the list of new motors to be purchased, the two main
items to specify are size and voltage
...
Since the load factor indicates how closely the motor size is matched to the driven load, it will in
some cases suggest downsizing a motor to make it operate at a more efﬁcient point in its load range
...
Another consideration is simply that a smaller motor will cost less
than one a size larger
...
Look to
size a new motor in the 75-90% load factor range rather than right at 100%
...

Vendor Selection
When the number of new motors desired at each horsepower size
and voltage was determined, a bid package was written up
...

Along with the bid price, we requested that the motor manufacturers submit their guaranteed minimum efﬁciency for each motor size
...
A new version of the master spreadsheet was created using the efﬁciency and cost data from each motor manufacturer
...

At the time of this project, one manufacturer provided motors with
efﬁciencies higher than any other motor across the range of sizes
...

After 10 and 20 years, the increased efﬁciencies led to signiﬁcant savings
...
Total man-hour time was approximately 600 hours
...

The procedure for installing energy-efﬁcient motors is identical to
the procedure for a standard motor
...
Allow extra time to transport and install these motors
...
Also be sure to follow closely the manufacturer’s recommendations
for greasing new motors
...
If utility
rebate money is involved, there may be restrictions on reusing the old
motors
...

When the new motors are installed, amp readings can be taken to
verify that the motors are in fact drawing less current (assuming that the
voltage and power factor have not changed signiﬁcantly)
...
When new pulleys and belts were installed along with
the new motor, the wrong pulley size was used, causing the increase in
current
...
This should be done after the motors have been operating for several weeks or more
...

A SIMPLIFIED APPROACH TO TESTING AND
EFFICIENCY CALCULATIONS
Motor efﬁciency is essentially a function of energy losses
...
Unfortunately, the
no-load test can be a very time-consuming procedure
...
Any method or procedure that further reduces the time required to determine load factor and
efﬁciency is a great beneﬁt to the energy manager
...

Since the ﬁeld testing phase of the Stanford project generated this kind of
data, we had an excellent basis for developing a simpliﬁed approach
...
This method eliminates the need for no-load
testing, as well as the load tests for motor speed and stator winding resistance
...

In order to understand our model, it is helpful to review some basic
efﬁciency and load factor relationships
...
Generally, efﬁciency increases with load factor, peaking at
approximately 75% load factor
...
Motor speed can also inﬂuence efﬁciency
...
The higher the slip, the lower the efﬁciency
(for a given motor size) and vice-versa
...

As shown in Formula 16-5, the load factor is in turn partially a
function of efﬁciency
...
” (This is how the CEC/PG&E model works
...
Since efﬁciency is relatively constant above 50% load, this
method will be quite accurate for that range
...
Now if we can use the input measurements and our estimate of L to determine the motor losses, we would be
able to calculate the operating efﬁciency
...
As discussed
in the section on motor basics, motor losses can be broken down into the
following:
Windage and Friction Losses (Wfw)
Core Losses (Wfe)
Stator Losses (Wcu)
Rotor Losses (Wr)
Stray Load Losses (Wsl)
Note that the last two are load-associated losses and the ﬁrst two are essentially independent of motor load
...

In order to build our model, we will need to make some assumptions
...
The key assumptions are:
Wsl* = 1
...
952 × HP
Wsl = Wsl* × L2
Wfw = 1
...
952 × HP
(Wfw is independent of load)
4
...

Wcu = Wcu* × (Ii/If)2
6
...
6 × Wcu*
(Wfe is independent of load)
7
...

2
...

Assumption 1 is suggested in IEEE Standard 112 testing method E,
while the others are based on results from our tests, as well as from other
literature
...
Summing the above expressions:
Wloss = (Wfw + Wsl + Wcu + Wfe + Wr)

(Formula 16-9)

Rearranging and then substituting terms,
Wloss = (Wfw [1 + L2) + Wcu + Wfe + (P – [Wcu + Wfe × S)
Wloss = (Wfw [ 1 + L2] + (Wcu + Wfe) (1 – S) + (P × S)
Wloss = [8
...
952 HP)] ×
[(Ii/If) 2 + 0
...
While this
would be quite tedious to calculate by hand each time, it only has to be
entered once into a spreadsheet and can be quickly copied for each set of
data
...
The composite
payback predicted by the simpliﬁed method is virtually identical to the
payback calculated with the PG&E/CEC computer program
...
The
simpliﬁed method is most accurate for motors between 10 and 50 horsepower
...

To summarize the steps involved in the simpliﬁed method:
1
...

Calculate Input Power
3
...

Calculate Slip (Formula 16-7)
5
...

Calculate Losses (Formula 16-10)
7
...

As mentioned, our model is based on the data we accumulated from

Efﬁcient Electrical Systems Design Handbook

380

a test group of 50 motors
...
In cases where time is a major concern, however, the simpliﬁed
method can be a great aid
...

As a ﬁnal note, the importance of operating hours in determining the
payback of energy-efﬁcient motor replacements should be emphasized
...
As a general rule, sites with very low operating hours seldom
show a favorable payback, while those operating year round almost always do, irrespective of efﬁciency and load factor
...

2
...

4
...

Lobodovsky, K
...
, et al
...

IEEE Standard 112, “Test Procedures for Polyphase Induction Motors and Generators
...
”
“Cost Analysis of Upgrading with Energy-Efﬁcient Motors,” Specifying Engineer
...
and Cadick, J
...

Guidelines for Implementing an Energy-efﬁcient Motor Retroﬁt Program

381

APPENDIX A
Efﬁciency Comparisons of Several Motors*

*Published by special permission: Energy Engineering, Vol
...
3, “Electric Motors Premium
vs
...
K
...

382

Efﬁcient Electrical Systems Design Handbook

Guidelines for Implementing an Energy-efﬁcient Motor Retroﬁt Program

383

Savings Calculation
To determine the savings realized from the difference in operating
cost between the high efﬁciency (premium) motor and standard efﬁciency
(standard) motor, use the following equation

S = 0
...
12; N = 4000; EA = 95; EB = 85; hp = 15

S = 0
...
12 x 4000 x 100 – 100
85
95
S = $665 per year
Simple Payback in Years =

Price Premium-Price Standard Motor
—————————————————
Total $ Saved Per Year

Evaluating Efﬁciency Using Life Cycle Costs:

LCS =
...
12

LCS = 746 x 15 x
...
”

References
1
...
F
...

2
...
J
...
, 5th
Edition
...
Industrial Lighting Handbook, National Lighting Bureau, Washington,
D
...

4
...
E
...
, N
...
, N
...

5
...
C
...
, N
...
, N
...

6
...
Y
...
Y
...

7
...
C
...
Energy Monitoring and Control Systems (EMCS), ARMY TM-8152, Departments of the Army and Air Force, June, 1994
...
Ottavianio, V
...
, Energy Management, Ottavianio Technical
Services Inc
...
National Electrical Code, National Fire Protection Association,
Batterymarch Park, Quincy, MA, 2008
...
Installation and Owner’s Manual, Trimax Controls Inc
...

12
...
, 2006
...
Thumann, A
...

14
...
, Plant Engineers & Managers Guide to Energy
Conservation, 8th Edition, Fairmont Press, 2002
...
The Engineering Basics of Power Factor Improvement, Specifying
Engineer
...
A New Look at Load Shedding, A
...

17
...
, Thumann, Electrical Consultant
...
An Efﬁcient Selection of Modem Energy—Saving Light Sources Can
Mean Saving of 10% to 30% Power Consumption, H
...
Anderson,
Electrical Consultant
...
Electric Power Distribution for Industrial Plants, The Institute of
Electrical Electronic Engineers
...
National Electrical Code: 2008
...
breakers 45
fuse types 50
G
Galvanometer 234
Galvanometer thermocouple
circuit 235
gas pressure relay 244
governor 245
GPW factor 279
gradient present worth 267, 269, 276
gradient present worth factor 270
grease life 356
grounding 313
grounding detail elevation 24
grounding plan 22
ground overcurrent relay 249
ground protective relay 245
ground sensor 251, 254
H
harmonics in the voltage,
additional 320
harmonic distortion 306
HID electronic ballast 175

Efﬁcient Electrical Systems Design Handbook

high-speed DC circuit breaker 244
high pressure sodium lamps 174
high quality rewinds 360
high quality rewinds added value
of 360
I
impedance 8
incandescent lamps 170
replacement 177
incomplete sequence relay 243
indirect glare 195
inductance 4
law 5
infrared sensor 183
input module 226
installations with the best payback
367
installation and follow-up 375
instantaneous overcurrent relay
(device 50) 243, 249
instrumentation 229
instrumentation wiring 236
instrument panel board schedule
23
instrument plan 22
interconnection diagram 24, 29, 215
interest factors 269
Internal Revenue Service 272
inverter 318
isolating contactor 241
isolation transformer shields 309
J
job requirements 29
K
Kirchoff’s Current Law 5
Kirchoff’s Voltage Law 5

Index

L
lamps per circuit, number of 192
lamp depreciation factor 178
lamp efﬁcacy 176
latches 228
language of the electrical engineer
19
level 232
control process 230
or ﬂow relay 244
life-cycle costing 267, 270, 278
life-cycle cost analysis 265
after-tax 276
lighting basics 167
lighting compensators 183
lighting control equipment 182
lighting control system 182
lighting efﬁciency 167
lighting panel 31
lighting panel board schedule 23
lighting plan 22, 30
lighting pole elevation 24
lighting quality 194
lighting terminology 169
lightning rod detail elevation 24
light emitting diodes (LEDs) 175
light loss factor (LLF) 179
light sources 170
line switch 247
liquid relay 244
load-resistor contactor 246
load factor 287, 377
load losses 369
load test 342, 361, 372
locked rotor test 342
locking-out relay 247
logic 209
logic gates 228
low pressure sodium lamps 175

391

low quality rewinds 354
lumen method 168
M
M
...
C

Title: Efficient Electrical Systems Design
Description: Efficient Electrical Systems Design

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