busbar protection areva
TRANSCRIPT
Busbar Protection
p:/applics/Powerpoint Cabinet/Training Courses/APPS1
January 2004
Alan WixonSenior Applications Engineer
> Busbar Protection – January 20043 3
Without Busbar Protection (1)
There are fewer faults on busbars than on other parts of the power system. No dislocation of system due to accidental operation of busbar
protection. Slow fault clearance.
Busbar faults at F1 and F2 are cleared by remote time delayed protection on circuits feeding the faults:
Time Delayed Overcurrent orTime Delayed Distance Protection
F2F1
> Busbar Protection – January 20044 4
Without Busbar Protection (2)
Fast clearance by breakers at the busbars
Where busbars are sectionalised,
Protection can limit the amount of system disruption for a busbar fault
BUSBARZONE
F2F1
> Busbar Protection – January 20045 5
Busbar Faults Are Usually Permanent
CAUSES :
Insulation failures
Circuit breaker failures
Falling debris
Isolators operated outside their ratings
Safety earths left connected
Current transformer failures
THEREFORE :
Circuit breakers should be tripped and locked out by busbar protection
> Busbar Protection – January 20046 6
Busbar Protection must be:
RELIABLE
Failure could cause widespread damage to the substation
STABLE
False tripping can cause widespread interruption of supplies to customers
DISCRIMINATING
Should trip the minimum number of breakers to clear the fault
FAST
To limit damage and possible power system instability
> Busbar Protection – January 20047 7
Methods of Providing Busbar Protection
Frame to Earth (Leakage) Protection
Differential Protection : High ImpedanceLow Impedance
Directional Comparison (Blocking Schemes) Protection
> Busbar Protection – January 20048 8
Frame Leakage Protection
> Busbar Protection – January 20049 9
Frame Earth Protection Scheme
Only an earth fault system
Involves measuring fault current from switchgear frame to earth
Switchgear insulated by standing on concrete plinth
Only one earthing point allowed on switchgear
C.T. mounted on single earth conductor used to energise instantaneous relay
All cable glands must be insulated
> Busbar Protection – January 200410 10
Current Distribution for External FaultOutgoing feeder
Switchgear frameSwitchgear framebonding bar
Generator
System earthingresistorEarth bar
Frame-leakage current transformer
Earthing electroderesistance (< 1Ω)
Frame insulation resistance to earth (> 10Ω)
IF = I1 + I2
I1 + I2
I1 I2I1
> Busbar Protection – January 200411 11
High Impedance Protection
> Busbar Protection – January 200412 12
High Impedance Protection (1)
This is a versatile and reliable protection system applied to many different Busbar configurations.
If CT requirements are met, scheme performance may be predicted by calculation without heavy current conjunctive tests.
> Busbar Protection – January 200413 13
High Impedance Protection (2)
Simple system to apply and extend.
High sensitivity for phase and earth faults.
Extremely stable for external faults.
CT requirements: Equal ratiosClass ‘X’
May require stabilising resistors, RST.
May require non-linear resistors (Metrosils).
RST
METROSIL87
> Busbar Protection – January 200414 14
Effective Setting
Since in each zone of protection there are several CT’s in parallel with the relay and each other, the combined CT magnetising currents will increase the primary operating current (P.O.C).
P.O.C. = CT ratio (IR + INLR + nIM)
where :-IR = Relay setting currentIM = CT magnetising current (one CT at relay
setting voltage)n = Number of paralleled CT’sINLR = Non linear resistor current at relay setting
voltage
> Busbar Protection – January 200415 15
Primary Operating Current (P.O.C)
The value of primary operating current should be around 30% of minimum fault current available. This ensures sufficient relay current during internal fault conditions for high speed operation.
> Busbar Protection – January 200416 16
Through Fault Stability
Busbar protection stability limit is based on maximum through fault current.
Generally this value is derived from the rating of the associated switchgear irrespective of existing fault level, since it can be expected that system will develop up to limit of rating.
> Busbar Protection – January 200417 17
Check Feature
Usually provided by duplication of primary protection using second set of CTs on all circuits other than bus section and coupler units. Check system forms one zone only, covering whole of busbar systems and not discriminating between faults on various sections.
Check zone
Zone A
Zone B87A
87A
87A
> Busbar Protection – January 200418 18
Current Transformers
> Busbar Protection – January 200419 19
CT Wiring Supervision (1)
Open circuit connections between CT’s and relay circuit result in unbalance currents which may operate the protection.
Supervision is applied by a voltage relay across differential relay circuit.
Supervision relay is time delayed, gives alarm and also shorts out bus wires to protect differential relay circuit.
Typical effective setting is 25 primary amps or 10% of lowest circuit rating, whichever is greater.
> Busbar Protection – January 200420 20
M3
SP
M3
SP
M2
SPSP
SP
M4M3M21
ZV
ZV
ZV
RV
relayn supervisio theoperate current to balance-of-OutV settingrelay n supervisio If
) // Z // Z // Z(R V relayn supervisioby measured Voltage
+++=Ι
=Ι=
CT Wiring Supervision (2)
I1
CT1
Supervisionrelay
VRST
RR
R ZM2 ZM3 ZM4
I1
I2 I3 I4
> Busbar Protection – January 200421 21
Differential Relay Circuit
ABCN
Zone bus wires
95X95X95X
Bus wire short contacts
Supervision relay
95
Stabilising resistors
87 87 87
v v v
Metrosilresistors
> Busbar Protection – January 200422 22
Current Transformer Wiring
Lead burdens between various sets of CT’s must be kept low. Usually buswires are run in closed ring between breaker control panels.
Typical route is :- CT’s to marshalling kiosk
Marshalling kiosk to isolator auxiliaries
Loop between marshalling kiosks
Conductor size :- Normally 2.5mm2
> Busbar Protection – January 200423 23
Effect of C.T. Location on Busbar Protection Performance
Busbarprotection
Circuitprotection
Circuitprotection
Busbarprotection
Overlapping C.T.s
Circuitprotection
Busbarprotection
Interlocked overcurrent relay
All C.T.s on line side of circuit breaker
All C.T.s on Busbar side of circuit breaker
Interlocked overcurrent relay
> Busbar Protection – January 200424 24
Busbar Arrangements
> Busbar Protection – January 200425 25
Typical Double Busbar Arrangement
60MWGenerators
75MVA132/13.8kVTransformers
132kV
> Busbar Protection – January 200426 26
Zones of Protection for Double Bus Station
Zone GZone H
Zone J
BC BC
BS
Typical Feeder Circuits
> Busbar Protection – January 200427 27
Isolator Auxiliary Switches
R
M
A B C D
a b c d
rm
Buswires
Auxiliary switches should :
1) Close before the isolator closes
2) Open after the isolator opens
In order to maintain stability on switching.
> Busbar Protection – January 200428 28
Tripping Circuits
One tripping relay (device 96) is required for each feeder breaker and 2 for each bus section or bus coupler breakers. Both main and check relays must be energised before tripping relays trip all breakers associated with zone.
> Busbar Protection – January 200429 29
Typical Trip Relay Arrangement
Double Busbar System
In Out
CSS - M1
CSS - M2
CSS - R
87M1 - 1
87M2 - 1
87R - 1
M1 RM2
a1
c1
b1
c2
D.C. Buswires
80T
96H2
96H1
96G
96F2
96F1
96E
96D2
96D1
-+87CH - 1
> Busbar Protection – January 200430 30
Double Busbar with Transfer Facilities
Main
Reserve / Transfer
By-passIsolator
By-passIsolator
> Busbar Protection – January 200431 31
Triple Busbar
Main
TransferCB
Transfer
Reserve
TransferCB
> Busbar Protection – January 200432 32
1½ Breaker Scheme
> Busbar Protection – January 200433 33
1½ Breaker Bus Protection
87
87
> Busbar Protection – January 200434 34
Mesh Busbar
T1
F1 F3
T4
T3
T2
F4 F2
> Busbar Protection – January 200435 35
Mesh Busbar Protection
T1
F1 F3
T4
T3
T2
F4 F2
87R1
87R3
87R4
87R2
> Busbar Protection – January 200436 36
Busbar Protection and Breaker Fail
Where breaker fail protection is applied to a system, back tripping of associated breakers is required in the event of a breaker failure.
Often, breaker fail protection is arranged in conjunction with busbar protection tripping circuits to initiate tripping of breakers on a busbar zone associated with the failed breaker.
> Busbar Protection – January 200437 37
Low Impedance Protection
> Busbar Protection – January 200438 38
Low Impedance Busbar Protection
Fast
Modular scheme design allows relays to relate to each circuit and function of the protection. This enables the user to easily understand the principles of application.
High sensitivity for phase and earth faults. Protection for each phase can be relatively independent.
Earlier schemes were less stable than high impedance schemes. Modern schemes incorporate saturation detectors and are extremely stable.
Duplicate measuring circuits are included.
Current transformers can be :
of different ratio
of relatively small output
shared with other protections
Current transformer secondary circuits are not switched.
Continuous supervision of CT circuits and constant monitoring of vital circuits are included.
> Busbar Protection – January 200439 39
Single Bus Protection
F1 F2 F3 F4
Z2Z1
BS
FM1
FM2
FM3
FM4BSM
Z1ZCK
Z2ZCK
ZCKZ1 Z2
> Busbar Protection – January 200440 40
Double Bus Protection
Z1
BCM1
Z3Z2Z4
BS
BC1 BC2F1 F2 F3 F4
BCM2
FM1
FM2
FM3
FM4BSM
Z1Z3ZCK
Z2Z4ZCK
Z1 Z2 Z4Z3 ZCK
> Busbar Protection – January 200441 41
Blocking Schemes
> Busbar Protection – January 200442 42
Busbar Blocking Protection
IF1
Incomer
O/C Relay
O/C Relay O/C Relay O/C RelayO/C Relay
BLOCK
IF2
> Busbar Protection – January 200443 43
Directional Comparison Busbar Protection
Bus zone protection and unit protection of feeders
Forward Forward Forward
F1 BS F2
F3 F4 F5 F6
DOC DOC DOC
OCOCOCOC