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Power Factor and Harmonics
Energy University Course Transcript
Slide 1
Welcome to Power Factor and Harmonics
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All these questions are basically linked to the control of Power Factor
and Harmonics
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On the road, this means that fuel mileage and reliability are not optimal, resulting

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In electrical installations, this means additional power losses
and reduced energy reliability
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Power factor
correction and harmonic mitigation provide immediate benefit in terms of reduced power losses, reduced
electricity bill, and the possibility to use the total system capacity
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For example, spot welding for car body assembly is sensitive to
voltage fluctuations linked to poor power factor
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Harmonics can cause protection devices to trip,
disrupting production and causing nuisance
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Slide 6
The presence of harmonics in electrical systems means that current and voltage are distorted and deviate
from sinusoidal waveforms
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The multiplying factor is called "harmonic order"
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A load is said to be
nonlinear when the current it draws does not have the same waveform as the supply voltage
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This results in disturbances of sensitive equipment, mainly related to the circulation of currents in
the grounding connections
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Such loads are increasingly
frequent in all industrial, commercial and even residential installations and their percentage in overall
electrical consumption is growing steadily
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The usual origin of voltage
fluctuation disturbances are motor start-up and spot welding
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Voltage fluctuations are the consequences of variable voltage drop along the distribution lines and across
transformer windings
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The advantages of reactive energy compensation or "power factor
correction" will be shown later in this course; but first, let’s talk a bit about power factor
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The electrical active power is transformed into mechanical power, heat or light
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The apparent power is the basis for electrical equipment rating
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Slide 9
For sinusoidal (undistorted) voltage and current, a vector representation is possible and helpful
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The current vector I can be split into 2 components:
 Ia is called the "active" component of the current, and
 Ir is called the "reactive" component of the current
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Thus, we define apparent power, active power and reactive power, as you see here
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Its important to note however, in a three phase system, these equations change just a bit
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Apparent power: S = √3 x U x I (kVA)
Active power: P = √3 x U x I x cos phi (kW)
Reactive power: Q = √3 x U x I x sin phi (kvar)
Here, U is the phase to phase voltage
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This can be accomplished by working through the power triangle calculation
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Let’s look at the power triangle in more depth
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The figure
illustrates the relationship of active (real) and reactive (imaginary or magnetizing) power
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This component is
the energy transfer component, which represents fuel burned at the power plant
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Magnetizing power is inherently present in transformers
and motors
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The longest leg of the triangle, labeled apparent power, represents the vector sum of the reactive power and
the real power components
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As the apparent power is the basis for electrical equipment rating, there is a big benefit to reduce the
reactive power, for a given amount of active power transferred to the loads
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Here we see the typical value of Power Factor for different kinds of electrical equipment
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8)
Incandescent lamp (1)
Compact fluorescent lamp (0
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6)
Resistance oven (1)
Computer (0
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Slide 12
A facility is operating with a demand of 4000 kW
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How many kvar
are required to bring the power factor back to unity? Looking at the information we have been given it
makes the most sense to use the power triangle formula:
kvar2 = kVA2 – kW2

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Slide 13
Consider a 200 HP electric motor that has the following information on the name plate:
460 volts
228 amps
Three phase
93% efficient
All at full load
What is the power factor of this motor?
Remember the power factor ratio:
PF = kW / kVA = active power / apparent power
First calculate the kW rating of the motor from the horsepower using the formula
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Therefore you must not only convert
from horsepower to kW, but must also calculate the input power from the output power
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1 HP = 0
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746 kW x Load factor / Efficiency
The data given told us that the motor is at full load, so that is 100% or 1
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93
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746 kW x 1 /0
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4 kW
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In a three phase system, kVA = √3 x U x I (and remember - U is the phase to phase voltage)
kVA = 1
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7
Take that one step further…
PF = 160
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7 = 0
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All rights reserved
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Slide 14
For many types of electrical equipment the difference between apparent power (VA) and active or real
power (W) is very slight and can be ignored
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Many desktop personal computers present a nonlinear load to the AC supply
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In a study done by PC Magazine, it
was found that typical personal computer systems exhibit a power factor of
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These devices present a very
linear load to the AC supply and do not generate harmonic currents
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Ten years ago, these devices were nonlinear loads like personal
computers, but today all of these loads are subject to international regulation IEC 1000-3-2 which require
them to be made with the "Power Factor Corrected" design
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Slide 15
The maximum active power is transmitted to a load when voltage and current are undistorted and in phase
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The average power is then reduced
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The average power is then also reduced
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Slide 16
Let's compare three different situations
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For a given transferred active power, the rms current is equal to I
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With displacement power factor (abbreviated to DPF) = cos phi = 0
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43 x I, so
it is increased by more than 40% for the same active power
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THDi is an indicator of the amount of distortion on the signal
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41 x I, so again increased by more than 40%
for the same active power
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Slide 17
The higher current means additional losses, more CO2 emissions, premature aging of equipment, higher
electricity cost, nuisance tripping of over-current detection relays, higher equipment cost, and possible
voltage fluctuations
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That is why power factor correction (PFC) and proper harmonic mitigation contribute to improve
competitiveness of companies in different ways:
 Reduced overloading on the electrical system, thereby releasing useable capacity
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Let’s take a closer look at the benefits of power factor correction and harmonic mitigation
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Both aspects are part of the electricity bill paid to the Electricity utility
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• Reduced cable size
The cable size is determined according to the electrical current requirements, so reduced current means
less expensive and easier-to-install cables
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The same problems may be produced by a high level of distortion, producing disturbances of
sensitive equipment (computer management system, sensors)

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Opex is reduced by reduction of power losses, reduction of subscribed power, and elimination of reactive
energy penalties
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Now that we have discussed the benefits of power factor correction and harmonic mitigation, let’s talk about
how best to mitigate those problems
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For example, monitoring can indicate whether the
disturbance originates inside or outside the installation
• Validation of quality contract compliance
Some examples of Monitoring Equipment include:
• Power monitors and circuit monitors: PowerLogic PM, CM, and ION Series’
• Protection relays: Sepam
• Trip units: Micrologic
Some examples of solutions include:
• Capacitor banks: Varset
• Transient-free capacitor switching: Varset Fast
• Harmonic filters: Accusine, Sinewave
• Fast reactive energy compensators: Accusine, Sinewave
Let’s discuss these solutions in further detail
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The main objective is to avoid reactive
energy penalties charged by the utility
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Compensation of an installation is determined in 4 steps:
1
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Selection of compensation mode (global, by sector, local)
3
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Consideration of harmonics
Slide 22
The first step is calculation of reactive power
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This is based on the formula we see here: Qc = P
(tan phi – tan phi')

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A facility has a demand of 3500 kW and a power factor of 0
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What size of
capacitor would be required to improve the power factor to 0
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Here we see that is 0
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8
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9, which means tan phi' equals 0
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Looking at our formula, the reactive power to be installed is Qc = 3500 * (0
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48) = 1120 kvar
Slide 23
The second step is selection of compensation mode (global, by sector, local)
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This is ideal for stable and continuous loads
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This is ideal for extended installations including workshops with varying load systems
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This is the best technical solution because reactive energy is supplied
where it is needed
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This arrangement uses one or more capacitor(s) to provide a constant level of compensation
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 These capacitors are applied:
 At the terminals of inductive loads (mainly motors),
 At busbars supplying numerous small motors and inductive appliances for which individual
compensation would be too costly, in cases where the load factor is reasonably constant
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This kind of compensation provides automatic control and adapts the quantity of reactive power to the
variations of the installation in order to maintain the targeted cos phi
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Where the kvar rating of the capacitors is less than, or equal to 15% of the supply transformer rating, a fixed
value of compensation is appropriate
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Control is usually provided by contactors
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And finally we’ll discuss dynamic compensation
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The principle of dynamic compensation is to associate a fixed capacitor bank and an electronic
var compensator, providing either leading or lagging reactive currents
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Slide 25
Now let’s look at the final step: Consideration of harmonics
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The selection is based on the value of the Gh/Sn ratio, as illustrated here
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When Gh/Sn exceeds 25%, a series reactor is necessary to limit the
circulation of harmonic currents, harmful to the capacitors
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Passive filters are implemented when power factor correction is requested with a high level
of existing harmonic distortion
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configuration, tuned to the frequency of the harmonic order to be eliminated
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Here we have discussed consideration of harmonics when selecting a capacitor bank for power factor
correction
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Slide 26
First, we have active filters
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The active filter
injects, in opposite phase, the harmonics drawn by the load, such that the line current remains sinusoidal
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Hybrid filters are systems including a passive filter and an active filter in a
single unit
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Slide 28
Active or hybrid filters are also capable of compensating the fluctuations of reactive energy
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Let’s move on now to discuss mitigating variable speed drive (VSD) power problems
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This solution, which is dedicated to centrifugal pumps, fans and
HVAC machines, has been adopted by leading manufacturers
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When a large number of drives are present within an
installation, the use of AC-line or DC-link chokes for each individual drive is recommended
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Precondition is a dedicated transformer directly supplied from the MV network, with a 3-winding
arrangement
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Multi-pulse solutions are the most efficient in terms of power losses
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Slide 32
The best performing solution concerning harmonic mitigation with drives is an electronically controlled
circuitry, called "Active Front End" (AFE), limiting the THDi below 5%
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No detailed system evaluation is necessary, making this solution the easiest to
implement
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Slide 33
As we conclude let’s review how appropriate design affects energy efficiency
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Power factor correction and Harmonic mitigation have an impact on all 3 aspects, since these allow:
 Reduction of the power losses in transformers, cables, switchgear, motors, capacitors, up to 5%,
 Eliminate utility charges for reactive energy (kvarh)
 Reduction of the demand power (in MVA), resulting in lower tariffs,
 Use of the total system capacity, without risk of overload, nuisance tripping or premature aging of
equipment
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Power factor and harmonic phenomena include power losses, overloading of the electrical system,
light flickers, disturbance of sensitive equipment, and nuisance tripping of circuit breakers
The impacts of these phenomena include increased utility bills for reactive power and power
losses, inability to use the full electrical system capacity, loss of production due to power outage,
and reduced equipment lifetime
Common causes of low power factor include motors, fluorescent lamps, discharge lamps, personal
computers

© 2012 Schneider Electric
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All trademarks provided are the property of their respective owners
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© 2012 Schneider Electric
...
All trademarks provided are the property of their respective owners

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