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05/02/031
Busbar Protection
Protection & Contrle / Application
Rev. A JM, September 2004
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Without Busbar Protection
F2F1
There are fewer faults on busbars than on other parts of the
power system.
No risk of dislocation of system due to accidental operation of
busbar protection.
Argues
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Without Busbar Protection
F2F1
Slow fault clearance.
Busbar faults at F1 and F2 are cleared by remote time
delayed protection on circuits feeding the faults:
Time Delayed Overcurrent or
Time Delayed Distance Protection
Drawbacks
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With Busbar Protection
BUSBARZONE
F1
Fast clearance by breakers at the busbars
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With Busbar Protection
BUSBARZONE
F2F1
Where busbars are sectionalised,
Protection can limit the amount of systemdisruption for a busbar fault
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21 21
87BB
87BB
1/2
With Busbar Protection
SS1
SS2
SS3
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21 21
87BB
87BB
2/2
With Busbar Protection
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21 21 21
21 21
1/2
With NoBusbar Protection
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21 21
2/2
21
21 21
With NoBusbar Protection
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21 21 21
21 21
21 21
87BB
87BB
With Busbar protection
With NoBusbar protection
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Busbar Faults Are Usually Permanent
Causes of Busbar Faults :
Falling debris
Insulation failures
Circuit breaker failures
Current transformer failures Isolators switchs operated on load or outside their ratings
Safety earths left connected
Therefore :
Circuit breakers should be tripped and locked out by busbar
protection
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Busbar Protection must be :
RELIABLE
Failure to trip could cause widespread damage to the substation
STABLE
False tripping can cause widespread interruption of supplies to
customers / possible power system instability
DISCRIMINATING
Should trip the minimum number of breakers to clear the fault
FAST
To limit damage and possible power system instability
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Methods of Providing Busbar Protection
Frame to Earth (Leakage) Protection
Blocking Scheme Protection
Differential Protection : High Impedance
Low Impedance
Insulation
>I
>I >I >I >I>I
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Frame Leakage Protection
Protection & Contrle / Application
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Insulation
>I
Frame Leakage Busbar Protection
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>I
Frame Leakage Busbar Protection
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>I
Frame Leakage Busbar Protection
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>I
Frame Leakage Busbar Protection
>I
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Can detect only earth faults
Switchgear must be insulated from earth (by standing onconcrete plinth)
Only one single earth conductor allowed on switchgear
All cable glands must be insulated
Switchgear sections must be insulated
Frame Leakage Busbar Protection
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>I
>I
Frame Leakage Busbar Protection
Neutral Check
False Operationbecause inducedloop
No operationprevents from
false trip
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>I
>I
Frame Leakage Busbar Protection
Neutral Check
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>I
>I
Neutral Check
Frame Leakage Busbar Protection
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Blocking Scheme Protection
Protection & Contrle / Application
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>I >I >I >I>I
Blocking Scheme Busbar Protection
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>I >I >I >I>I
Blocking Scheme Busbar Protection
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>I >I >I >I>I
Blocking Scheme Busbar Protection
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High Impedance Protection
Protection & Contrle / Application
Rev. A JM, September 2004
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Single Bus Substation
Single Bus Substation
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P1
P2
S1
S2
P1
P2
S1
S2
P1
P2
S1
S2
Single Bus Substation
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Single Bus Substation
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Single Bus Substation
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Double Bus Substation
Isolator Auxiliary Switches
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yCurrent switching
Bus A
Bus B
ab
Current
P1
P2
S1
S2
P1
P2
S1
S2
P1
P2
S1
S2
P1
P2
S1
S2
P1
P2
S1
S2
Isolator Auxiliary Switches
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yCurrent switching
Bus A
Bus B
ab
Current
Isolator Auxiliary Switches
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yCurrent switching
Bus A
Bus B
ab
Current
Isolator Auxiliary Switches
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Current switching
Bus A
Bus B
ab
Current
Isolator Auxiliary Switches
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Current switching
Bus A
Bus B
ab
Current
Isolator Auxiliary Switches
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Current switching
Bus A
Bus B
ab
Current
Isolator Auxiliary Switches
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40 40
Bus A
Current
Bus B
ab
Tripping switching
Tripping ab
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41 41
Main CT must be identical
Current switching via auxilliary relay is not acceptable.
Requirement of number of position contact (Disconnectorswitch) is high
Interposing CT are not acceptable
Isolator Auxiliary SwitchesC t it hi
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42 42
Current switching
Bus A
Bus B
abCurrent
Isolator Auxiliary SwitchesC t it hi
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Current switching
Bus A
Bus B
abCurrent
Bus A
Bus B
abCurrent
Isolator Auxiliary SwitchesO L d T f
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Bus A
Bus B
a
bCurrent
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
abCurrent
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
abCurrent
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
abCurrent
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
ab
Current
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
abCurrent
On Load Transfer
Isolator Auxiliary SwitchesOn Load Transfer
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Bus A
Bus B
abCurrent
On Load Transfer
Isolator Auxiliary SwitchesCheck Zone
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Bus A
Bus B
TripBusA
TripBusB
Zone A
Zone B
Check Zone
Isolator Auxiliary SwitchesCheck Zone
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Bus A
Bus B
TripBusA
TripBusB
Zone A
Zone B
Check Zone
Current
switching
failure
False
Tripping
Isolator Auxiliary SwitchesCheck Zone
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Bus A
Bus B
TripBusA
TripBusB
Check
Zone
Zone A
Zone B
Check Zone
Isolator Auxiliary SwitchesCheck Zone
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Bus A
Bus B
TripBusA
TripBusB
Zone A
Zone B
Check Zone
Isolator Auxiliary SwitchesCheck Zone
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Bus A
Bus B
TripBusA
TripBusB
Check
Zone
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One Breaker and a HalfSubstation
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Bus A Bus
B
P1
P2
S1
S2
P1
S1
P2
S2
P1P2
S1S2
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Bus A Bus
B
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Bus A Bus
B
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Bus A Bus
B
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Bus A Bus
B
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Bus A Bus
B
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Bus A Bus
B
P1
S1
P2
S2
P1
S1
P2
S2
P1
S1
P2
S2
P1
S1
P2
S2