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Title: Circuit Protection
Description: Construction and operation of circuit over-current protection devices and high power circuit breakers. Construction and operation. of ELCB and RCD devices. Definition of energy tariffs - two part structure. Effect of Power Factor on tariff.
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HNC Electrical and Electronic Engineering
Year Two - 2014/15
Module: UofEE

UTILISATION OF
ELECTRICAL ENERGY

Circuit Protection, Energy
Management and Tariffs
Keith A
...
Hudson

2

Utilisation of Electrical Energy
16 April, 2015

Contents
1

Circuit Over-Current Protection Devices (Task1)
...
1

Semi-Enclosed Fuse (BS3036)
...
2

High Rupture Capacity (HRC) Fuse (BS88 BS1361 BS1362)
...
3

Bulk Oil Circuit Breaker (BOCB)
...
4

Plain (Air) Break Circuit Breaker (ABCB)
...
5

Pressure Type Circuit Breaker
...
8

3

ELCBs and RCDs (Task3)
...
1
3
...
9
RCD
...
10
4
...
10

4
...
1

Maximum Demand
...
1
...
10

4
...
3

Diversity Factor
...
1
...
10

4
...
10

4
...
11

4
...
12

5

Three-phase, 50HP, 415V Motor (Task 5)
...
15

7

Bibliography
...
Hudson

3

Utilisation of Electrical Energy
16 April, 2015

Figures
Figure 1: Fuse showing screw holding one end of the fuse wire
...
4
Figure 3: BLUE - 15A
...
4
Figure 5: HRC fuse construction (Electrical4U, 2015)
...
6
Figure 7: 3-phase BOCB
...
7
Figure 9: Puffer type SF6 circuit breaker (skm-eleksys
...
7
Figure 10: Voltage operated ELCB
...
9
Figure 12: RCD internal circuit
...
5
Table 2: Advantages and disadvantages of SF6
...
11
Table 4: Demand charges
...
12
Table 6: kVA calculation
...
13
Table 8: Power and current calculations @ PF 0
...
14
Table 9: Consumption charge @ PF 0
...
15
Table 10: Consumption charge @ PF 0
...
16
Table 11: Load factor calculation
...
com, 2015)

HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
1 Semi-Enclosed Fuse (BS3036)
A fuse is a device designed to be the weakest link in a circuit
...
e
...
It prevents higher than expected currents from damaging the rest of the circuit
...
This high current melts the wire in the fuse and in doing so the current can no
longer flow because the circuit is now open
...
k
...
re-wirable Fuse)
...
When the fuse blows, the wire can be easily (and cheaply) replaced
...
The most common ratings are 5, 15 and 30A
...
Unfortunately there is no easy
way to tell if the fuse holder has the correctly rated fuse wire
...
This will probably blow if a lower rating is used, but there is a risk of fire if higher rated wire is used
when a faulty piece of equipment is plugged in
...
This can have disastrous consequences
...
Hudson

Utilisation of Electrical Energy
16 April, 2015

5

Even if the correct wire is used, the fusing current cannot be as well controlled as an enclosed fuse
...
This type of fuse is not used in new
installations RCD are used instead
...
15

25

0
...
20

30

0
...
35

45

1
...
50

60

1
...
60

80

1
...
0

According to BS3036:1958, semi-enclosed fuses are rated up to 100A, 240V
...


1
...
The fusing element runs through the tube and is connects the end
caps
...
The end caps are brass and have tabs with stots or holes to screw the
fuse in place
...
This gives it a larger surface area than wire fuses, thus
improving heat dissipation
...
Another
improvement is to use several fusible elements rather than a single heavier current one
...


Figure 5: HRC fuse construction (Electrical4U, 2015)

The tube contains sand (granulated quartz / silica) to help with heat dissipation during normal operation and to
reduce arcing during short circuit
...
They have a breaking capacity of
80kA at 415V (550V) AC
...
If the short circuit condition is rectified in that time the HRC fuse does not blow
...
Hudson

6

Utilisation of Electrical Energy
16 April, 2015

1
...
The same mineral oil is used as transformer
insulating oil
...
A BOCB was typically used by the power industry for high
voltage (>52kV) applications
...

When the contacts are moved apart an arc flows between the fixed and movable contacts
...
(The hydrogen comes from the oil which consists of hydro-carbons
...
The arc should be extinguished at the zero crossing point of the
alternating current/voltage, i
...
when the voltage and current are zero
...

The disadvantages of BOCB is that oil is flammable, hydrogen (plus oxygen) is explosive
...
The oil tanks need to be large and the higher the voltage, the
larger the tank required
...


1
...
By stretching
the arc the dielectric of the air-gap is increased
...
Once the
dielectric is greater than the voltage across the electrodes, the arc is extinguished
...
This travels up the contacts increasing in
length as it does so (see Figure 8A)
...

The plain-break circuit breaker is suitable for voltages between 120V - 15 kV
...


HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
5 Pressure Type Circuit Breaker
The pressure type circuit breaker uses sulphur-hexafluoride (SF6) gas
...
When the breaker operates the gas is released through the arc to quench it
...

Modern HF8 breakers (known as puffers) compress the gas while opening the contacts
...
The movable one is attached to a movable cylinder
...
As the contact moves away from the fixed contact, the cylinder moves,
compressing the SF6
...
The arc is quenched when
the current reaches the zero-crossing point
...
com, 2015)

HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
It is typically
used by the power industry for high voltage (>52kV) applications
...

Table 2: Advantages and disadvantages of SF6

Advantages

Disadvantages

High ,dielectric strength is ideal for arc quenching,
reduced arc time, increased current handling

Operation requires much higher mechanic energy than
an oil circuit breaker
...


Some of the gas is broken down by the arc, producing
other fluorides of Sulphur
...


Greenhouse gas 23,900 times worse than CO2
...


More expensive than oil based circuit breakers
...


2 Circuit Breakers

(Task2)

The purpose of a CB is to safely protect the electrical distribution network
...

ο‚· Remain open withstanding voltage across the contacts without breakdown of the di-electric
...

Air-blast CB were prevalent in the 1960’s
...
There are
still many in operation today, but SF6 is now dominant
...
SF6 CBs can now switch up
to 1,100 kV, 80 kA, and 50 GVA
...

The future of CB technology is using superconducting fault current limiters (SFCLs)
...
As with most new technological developments, costs are the main factor inhibiting
market dominance
...
Hudson

9

Utilisation of Electrical Energy
16 April, 2015

3 ELCBs and RCDs

(Task3)

Voltage earth-leakage circuit breakers (ELCB) and residual current device (RCD) are electrical safety devices
...
1 ELCB
The ELCB detects fault currents from the live to the
earth within the connected equipment
...
The
ELCB remains β€œtripped” until it is reset
...
The equipment
body could be live, which could result in injury or fire
...

RCDs are now used
...
If the wrong type was used, however, the level of
protection would be substantially less than that expected (Parmar, 2015)
...


3
...

The secondary winding is used as a sensing coil, connected to a relay or solid state switching device, the operation of
this activates the tripping mechanism
...
Hudson

10

Utilisation of Electrical Energy
16 April, 2015

When the line and neutral currents are balanced, the net magnetic fluxes is zero so no current is induced in the
sensing coil
...
A current is
induced in the secondary winding which activates the tripping mechanism

4 Energy Tariffs

(Task4)

4
...
1
...
It is
usually measured in kW (sometimes kVA)
...
)
4
...
2 Load Factor
Load factor is the utilization rate (i
...
the efficiency of energy use)
...
e
...

It is the total electricity used (kWh) in a given billing period against maximum demand (kW) multiplied by the
number of hours (h) in the billing period
...
)
4
...
3 Diversity Factor
The diversity factor a ratio of the sum of individual maximum demands for all equipment against the maximum
demand for the whole system
...
It is the total installed load versus currently running load
...
π‘‘π‘’π‘šπ‘Žπ‘›π‘‘
π‘ƒπ‘™π‘Žπ‘›π‘‘ π‘šπ‘Žπ‘₯
...
It has no units
...
1
...
e
...

π·π‘’π‘šπ‘Žπ‘›π‘‘ πΉπ‘Žπ‘π‘‘π‘œπ‘Ÿ =

π΄π‘£π‘’π‘Ÿπ‘Žπ‘”π‘’ π‘π‘œπ‘€π‘’π‘Ÿ
Maximum demand
=
π‘ƒπ‘’π‘Žπ‘˜ π‘π‘œπ‘€π‘’π‘Ÿ
Total connected load

(Demand factor ≀ 1
...
)

4
...

Capital expenditure covers the one-off cost to build the plant and distribution network or work to extend the life or
capacity of the plant
...

HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
It includes plant maintenance, fuel costs such as coal or gas used to drive the generators
...

In general a customer pays a fixed standing charge for each billing period
...

They also pay for the amount of electricity used in the billing period
...

π‘‡π‘Žπ‘Ÿπ‘Ÿπ‘–π‘“ = π‘†π‘‘π‘Žπ‘›π‘‘π‘–π‘›π‘” πΆβ„Žπ‘Žπ‘Ÿπ‘”π‘’ + (π‘ƒπ‘’π‘Ÿ 𝑒𝑛𝑖𝑑 π‘π‘œπ‘ π‘‘ βˆ— 𝑒𝑛𝑖𝑑𝑠 𝑒𝑠𝑒𝑑)
Fuel costs are usually fixed annually but significant changes might incur an additional fuel surcharge, which will be
added to the per-unit-cost and passed on to the customer
...
The first so many hundred
units are at a high rate, any units thereafter are at a lower rate
...
For that
reason the following examples will be based on Hong Kong tariffs
...

Domestic – home use
...

General service – home/small business use
iii
...

iv
...

(Note: prices are Hong Kong dollars/cents
...
3 Domestic Tariff
Table 3: Domestic tariff standard costs

Total Monthly
Consumption

Control Rebate Scheme
(cents)

Net Rate (cents

First 400 units

86
...
6

85
...
2

0
...
6

Next 800 units

99
...
6

99
...


Tariff Rate (cents)

108
...
6

107
...
This is called
the fuel clause adjustment
...
Hudson

ii
...


Utilisation of Electrical Energy
16 April, 2015

12

There is a rebate of 2
...

Regardless of units used and adjustments, the minimum bill shall be β‰₯$30
...
4 Large Power Tariff
The bill for this tariff shall be calculated from the addition of the following elements:
Table 4: Demand charges

kVA

Cost/kVA ($)

≀5,000 kVA

117
...
0

Each kVA up to peak demand kVA

0
...
0

Peak Period

Off-peak Period

Table 5: Energy charge

Total Monthly
Consumption

Net Rate
(cents)

53
...
6

53
...
5

0
...
9

Off-peak Period
Per kVA

ii
...


Control Rebate
(cents)

On peak Period
First 200 units
Per kVA

i
...
0

0
...
4

The unit cost will be adjusted if the cost of 44 GJ of generating fuel is more (or less) than $700
...

There is a rebate of 2
...

Regardless of units used and adjustments, the minimum bill shall be 35 units per kVA of demand
...
Hudson

Utilisation of Electrical Energy
16 April, 2015

13

5 Three-phase, 50HP, 415V Motor

(Task 5)

The motor operates at full load, 0
...

Table 6: kVA calculation

πΎπ‘›π‘œπ‘€π‘› π‘£π‘Žπ‘™π‘’π‘’π‘ 
3 π‘β„Žπ‘Žπ‘ π‘’, π‘…π‘Žπ‘‘π‘’π‘‘ π‘π‘œπ‘€π‘’π‘Ÿ = 50 β„Žπ‘

𝑃𝐹 = 0
...
745699872 π‘˜π‘Š
50 β„Žπ‘ = 50 Γ— 0
...
2849936 π‘˜π‘Š
𝑃 π‘€π‘’π‘β„Ž
𝑃 π‘…π‘’π‘Žπ‘™

= 85% =

𝑃 π‘…π‘’π‘Žπ‘™ =

πΈπ‘™π‘’π‘π‘‘π‘Ÿπ‘–π‘π‘Žπ‘™ π‘ƒπ‘œπ‘€π‘’π‘Ÿ
(π‘…π‘’π‘Žπ‘™ π‘ƒπ‘œπ‘€π‘’π‘Ÿ)

𝑃 π‘…π‘’π‘Žπ‘™ =

100
85
100
85

85
100

Γ— 𝑃 π‘€π‘’π‘β„Ž
Γ— 37
...
86469835
𝑃 π‘…π‘’π‘Žπ‘™ = 43
...
)

Table 7: Apparent power and current calculation

𝑃 𝐴𝑝𝑝 =
π΄π‘π‘π‘Žπ‘Ÿπ‘’π‘›π‘‘ π‘ƒπ‘œπ‘€π‘’π‘Ÿ
(π‘˜π‘‰π΄ π‘‘π‘’π‘šπ‘Žπ‘›π‘‘)

𝑃 𝐴𝑝𝑝 =

𝑃 π‘…π‘’π‘Žπ‘™
𝑃𝐹
43
...
7

𝑃 𝐴𝑝𝑝 = 62
...
66 π‘˜π‘‰π΄ (2𝑑
...
Hudson

𝐼=
πΆπ‘’π‘Ÿπ‘Ÿπ‘’π‘›π‘‘

Utilisation of Electrical Energy
16 April, 2015

14
𝑃 𝐴𝑝𝑝
𝑉 𝐿𝐿

=

62
...
15099724 π‘˜π΄
𝐼 = 150
...
)

Table 8: Power and current calculations @ PF 0
...
86469835

𝑃𝐹 = 0
...
86469835
0
...
17336668 π‘˜π‘‰π΄
𝑃 𝐴𝑝𝑝2 = 46
...
)
= 𝑃 𝐴𝑝𝑝 βˆ’ 𝑃 𝐴𝑝𝑝2
= 62
...
17336668

πΆβ„Žπ‘Žπ‘›π‘”π‘’ 𝑖𝑛 π΄π‘π‘π‘Žπ‘Ÿπ‘’π‘›π‘‘ π‘ƒπ‘œπ‘€π‘’π‘Ÿ
= 16
...
5 π‘˜π‘‰π΄ (1𝑑
...
17336668
415

𝐼2 = 0
...
)

HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
99724 βˆ’ 111
...
736116 𝐴
= 39
...
)

6 Pottery Manufacturer

(Task 6)

Table 9: Consumption charge @ PF 0
...
8 π‘™π‘Žπ‘”π‘”π‘–π‘›π‘”
π‘‡π‘Žπ‘Ÿπ‘–π‘“π‘“
Β£7
...
5𝑝/π‘˜π‘Šβ„Ž

π‘ƒπ‘’π‘Žπ‘˜ π·π‘’π‘šπ‘Žπ‘›π‘‘ (π‘‡β„Žπ‘’ β„Žπ‘–π‘”β„Žπ‘’π‘ π‘‘ 𝑙𝑒𝑣𝑒𝑙 π‘œπ‘“ π‘‘π‘’π‘šπ‘Žπ‘›π‘‘ 𝑖𝑛 π‘‘β„Žπ‘’ π‘šπ‘œπ‘›π‘‘β„Ž)
πΏπ‘–π‘”β„Žπ‘‘π‘–π‘›π‘” 𝑒𝑑𝑐 𝑝𝑙𝑒𝑠 π‘‘π‘€π‘œ π‘˜π‘–π‘™π‘›π‘ 

20 + (50 Γ— 2) = 120
π‘ƒπ‘’π‘Žπ‘˜ π·π‘’π‘šπ‘Žπ‘›π‘‘ = 120 π‘˜π‘Š
π‘‡π‘œπ‘‘π‘Žπ‘™ π‘˜π‘Šβ„Ž

πΏπ‘–π‘”β„Žπ‘‘π‘–π‘›π‘” 𝑒𝑑𝑐, 8 β„Žπ‘œπ‘’π‘Ÿπ‘  π‘π‘’π‘Ÿ π‘‘π‘Žπ‘¦,
23 π‘‘π‘Žπ‘¦π‘  π‘π‘’π‘Ÿ π‘šπ‘œπ‘›π‘‘β„Ž @ 20 π‘˜π‘Š

HNC Electrical and Electronic Engineering

8 Γ— 23 Γ— 20 = 3,680 π‘˜π‘Šβ„Ž

Year Two: 2014/15

Keith A
...
8

= 150 π‘˜π‘‰π΄

π·π‘’π‘šπ‘Žπ‘›π‘‘ πΆβ„Žπ‘Žπ‘Ÿπ‘”π‘’
πΆπ‘œπ‘›π‘ π‘’π‘šπ‘π‘‘π‘–π‘œπ‘› π‘β„Žπ‘Žπ‘Ÿπ‘”π‘’ 𝑖𝑠
0
...
085 Γ— 4,480 = 380
...
00 π‘‘π‘–π‘šπ‘’π‘  π‘›π‘’π‘šπ‘π‘’π‘Ÿ π‘œπ‘“ π‘˜π‘‰π΄ π‘œπ‘£π‘’π‘Ÿ 𝑑𝑒𝑛

7 Γ— (150 βˆ’ 10) = 7 Γ— 140 = 980
...
80 + 980
...
80

Table 10: Consumption charge @ PF 0
...
97
π‘˜π‘Š

𝑃=

𝑃𝐹

120
0
...
7 π‘˜π‘‰π΄ (1𝑑
...
085 π‘‘π‘–π‘šπ‘’π‘  𝑒𝑛𝑖𝑑𝑠 𝑒𝑠𝑒𝑑

0
...
80

π‘‚π‘£π‘’π‘Ÿ π‘˜π‘‰π΄ π‘β„Žπ‘Žπ‘Ÿπ‘”π‘’ 𝑖𝑠
7
...
7 βˆ’ 10) = 7 Γ— 113
...
98

π‘‡π‘œπ‘‘π‘Žπ‘™ π‘‘π‘’π‘šπ‘Žπ‘›π‘‘ π‘β„Žπ‘Žπ‘Ÿπ‘”π‘’

380
...
98 = Β£1,176
...
Hudson

πΆβ„Žπ‘Žπ‘›π‘”π‘’ 𝑖𝑛 π‘‘π‘’π‘šπ‘Žπ‘›π‘‘ π‘β„Žπ‘Žπ‘Ÿπ‘”π‘’

Utilisation of Electrical Energy
16 April, 2015

17

1,360
...
78 = Β£184
...
34782609
= 24
...
)
𝐿𝐹 =

πΏπ‘œπ‘Žπ‘‘ πΉπ‘Žπ‘π‘‘π‘œπ‘Ÿ

𝐿𝐹 =

𝐴𝑣𝑔 π·π‘’π‘šπ‘Žπ‘›π‘‘
π‘€π‘Žπ‘₯ (π‘ƒπ‘’π‘Žπ‘˜) π·π‘’π‘šπ‘Žπ‘›π‘‘
24
...
00

=

14
69

𝐿𝐹 = 0
...
20 (2𝑑
...
Hudson

18

Utilisation of Electrical Energy
16 April, 2015

7 Bibliography
AutomationDirect
...
Industrial Circuit Protection Products
...
automationdirect
...

Cary, S
...
, 2013
...
[Online]
Available at: http://www
...
com/ecm/groups/public/@pub/@electrical/documents/content/wp012001en
...

EDF Energy, 2015
...
[Online]
Available at: http://www
...
com/large-business/glossary
[Accessed 29 05 2015]
...
Electrical Fuse HRC Fuse High Rupturing Capacity | Electrical4U
...
electrical4u
...

Flameport Enterprises Ltd, 2015
...
[Online]
Available at: http://www
...
com/electric_museum/old_fuses/index
...

Metwally, I
...
IEEE Xplore Abstract - New technological trends in high-voltage power circuit breakers
...
ieee
...
jsp?tp=&arnumber=4013573&url=http%3A%2F%2Fieeexplore
...
org%2Fxpls%
2Fabs_all
...

Open Electrical , 2013
...
[Online]
Available at: http://www
...
org/wiki/index
...

Parmar, J
...
Demand Factor-Diversity Factor-Utilization Factor-Load Factor
...
wordpress
...

Parmar, J
...
Working Principlesof Earth Leakage Circuit Breaker (ELCB)
...
com/working-principle-of-earth-leakage-circuit-breaker-elcb-andresidual-current-device-rcd
[Accessed 31 05 2015]
...
Electrical Demand - Load Factor
...
demandcharge
...
html
[Accessed 30 05 2015]
...
com, 2015
...
[Online]
Available at: http://www
...
com/convert/power/hp-to-kw
...

HNC Electrical and Electronic Engineering

Year Two: 2014/15

Keith A
...
com, 2015
...
[Online]
Available at: http://www
...
com/2012/02/sf6-circuit-breaker-working
...

Swardt, M
...
, 2014
...
[Online]
Available at:
http://www02
...
com/global/zaabb/zaabb011
...
pdf
[Accessed 29 05 2015]
...
paramount hrc
...
voltimum
...
uk/search/site/paramount%20hrc
[Accessed 27 05 2015]
Title: Circuit Protection
Description: Construction and operation of circuit over-current protection devices and high power circuit breakers. Construction and operation. of ELCB and RCD devices. Definition of energy tariffs - two part structure. Effect of Power Factor on tariff.
Buy These NotesPreview