Breaker Failure Protection

Breaker Failure Protection 1

Breaker Failure Protection


Backup Protection

Local backup is the additional (or secondary, redundant) protection provided for the primary zone to assure breaker trip if the primary relaying fails.

Remote backup is the overlapping of the primary zone provided by remote (adjacent busses) protection that will operate, after a suitable coordinating time, if the primary zone breaker does not trip. Relays at 1 protecting line AB are also remote backup to relays at 3 protecting line BC.

Breaker failure is initiated when the primary and/or local backup relays have operated and the local breaker fails to trip.

Fault X

A1 2

5 6

3

7 8

4

D E

CB


Backup: Local, Remote and Breaker Failure

Local Backup Relays

Remote Backup Relays

Primary Relays

50BF

Trip Local Breaker

Trip Local Adjacent Breakers

Trip Remote Breaker

62BF

Remote Backup Relay Time Delay

Breaker Failure Relay


Remote Backup

Fault on line BC - Failure of breaker 3 to operate

Relays at 1,5 and 8 are backup to to relays at 3

Backup relays may not see fault due to infeed

Coordination time may be undesirably slow

Sequential remote tripping• If one remote can see the fault and clear there will be a

redistribution of fault currents reducing the effect of infeed• The second remote relay will trip eliminating infeed• The last remote relay will trip

Fault X

A1 2

5 6

3

7 8

4

D E

CB


Breaker Failure

EHV and UHV Applications

• Greater fault currents produce more stress on power circuit breakers

• Stability demands for faster backup clearing – Critical Clearing Time

Thus, Local Breaker Failure

• Breaker failure does not preclude remote backup


Breaker Failure and Remote Backup

Fault on line BC and relays at 1, 2 and 5 operate

Breakers 1 and 5 trip - breaker 2 fails to operate

Breaker failure at 2 trips breaker 3 and removes any infeed seen by relays at 4

Relays at 4 will operate as remote backup to clear fault

Transfer tripping of breaker 4 by breaker failure at 2 is also possible

CFault X

A

1

2

3

4

B

5


Breaker Failure Scheme

50 - Phase and ground instantaneous overcurrent relays

52a - Breaker auxiliary contact, open when breaker is open

52T - Breaker trip coil

62X,Y - Breaker failure auxiliary (BFI)

62BF - Breaker failure timer

86BF - Breaker failure lockout relay

94 - Breaker trip relay (used for single trip coil applications)

Relay Scheme

#2

52a

94 62Y

+ dc

- dc

94Relay

Scheme #1

52a

52T

62X

+ dc

- dc

62X

+ dc

- dc

62BF

62 BF

62Y

86BF

50

Multiple 86BF

Contacts86 BF


Breaker Failure Logic

T0

62X62Y

5086BF52a

52a86T 62BF

50 - Phase and ground instantaneous overcurrent relays

52a - Breaker auxiliary contact, open when breaker is open

62X,Y - Breaker failure auxiliary (BFI)

62BF - Breaker failure timer

86BF - Breaker failure lockout relay

86T - Transformer differential lockout

Options


Single-line Single-breaker Bus

1 Line 1

2 Line 2

3 Line 3

N Line N

50 BF

Line Relays 62X,Y

62X,Y 50BF-1

62X,Y 50BF-2

62X,Y 50BF-3

62X,Y 50BF-N

62 BF

86 BF

Bus Arrangement Typical Logic


Breaker-and-a-half Bus

Line 1 Line 2

50 2

50 1

50 3

Line 2 Relays

Line 1 Relays

1 2 3

4Bus L

Bus R

BreakerFailure

86 RelayOperations

1 Trip 2 and all Bus Lbreakers.Transfer trip Line 1

2 Trip 1 and 3.Transfer trip lines 1 & 2.

3 Trip 2 and all Bus Rbreakers, such as 4.Transfer trip line 2


Ring Bus

Line 1

Relays

Relays

Line 250 1

50 2

Transformer Differential

1

2

3

4

50 3 Relays

Line 3

5

50 4

86T

Breaker Failure

86 Relay Operations

1 Trip 2 and 4 Transfer trip lines 1 & 2

2 Trip 1 and 3 Transfer trip lines 2 & 3

3 Trip 2, 4, and 5 Transfer trip line 3

4 Trip 1, 3, and 5 Transfer trip line 1



62X,Y - Breaker failure auxiliary (BFI) Include both line relay’s 62X, Y for common breaker• Breaker-and-a-half bus - center breaker• Ring bus

62X

+ dc

- dc

62BF

62 BF

62Y

86BF

50

86 BF

**

T0

62X 62Y

5086BF52a

52a86T 62BF

Options

**


Breaker Failure Time Chart

Relay Operate

Breaker Clearing

Normal Clearing Time50

ResetMarginNormal

Clearing

Failed Breaker

62X 62Y BFI

62BF Timer Setting86 BF

TFR TRIP

Local Backup Clearing

Remote Backup Clearing

Normal ClearingLocal Backup BF Total Clearing

Remote Backup BF Total Clearing


Breaker Failure

50BF Overcurrent Reset is affected by:• Breaker arcing contacts and shunting resistors • Fault current level prior to interruption• CT saturation• 50BF setting• Breaker-and-a-half and ring bus applications

Solid state relays have faster reset than electromechanical relays

Reset is generally assured to be within one cycle using microprocessor relays -this is dependent on sampling and computation rate



50BF - Phase and ground torque controlled instantaneous overcurrent relays

Relay cannot operate until after 62BF time

Fast pickup, 0.25 to 1.0 cycle depending on setting and fault current

Allows more sensitive setting

Control timer resets breaker failure operation

TR

62X62Y

50BF

Control Timer

T0

62BF Torque Control

86BF

Retrip


Breaker Failure Time Chart

Relay Operate

Breaker Clearing

Normal Clearing Time

50 Pickup

MarginNormal Clearing

Failed Breaker

62X 62Y BFI

62BF Timer Setting86 BF

TFR TRIP

Local Backup Clearing

Remote Backup Clearing

Normal ClearingLocal Backup BF Total Clearing

Remote Backup BF Total Clearing

Control Timer T (Setting) R


Critical Clearing Time

A maximum allowable time that a fault may persist before jeopardizing the integrity of the power system• System location• Loading• Fault type

Breaker failure clearing time including remote backup clearing must be less than critical clearing time


IPO Breakers

Independent Pole Operated Breakers• Single pole tripping and reclosing• Three pole tripping

– On breaker failure • the opening of two phases on a three-phase fault will

likely clear the fault or change the fault characteristic to single-phase-to-ground.

• Increase the maximum critical clearing time.

Pole Discrepancy detection becomes increasingly important


Pole Discrepancy

Based on auxiliary 52a and/or 52b contact positions

Based on breaker current level


Pole Discrepancy

Auxiliary contact arrangement for three pole gang operated breaker position indication


Pole Discrepancy

Auxiliary contact arrangement for IPO breaker position indication

Using 52a - parallel• 52a = 0 (All poles open)

• 52a = 1 (Any pole closed)

Using 52b - series• 52b = 1 (All poles open)

• 52b = 0 (Any pole closed)

CIRCUIT BREAKER

52a

A

A

A

B

B

B C

C

C

52b

Breaker Position

Breaker Position

52a

52a

52b 52b


Pole Discrepancy

Auxiliary contact arrangement for IPO breaker position indication

Using 52a - series• 52a = 0 (Any pole open)

• 52a = 1 (All poles closed)

Using 52b - parallel• 52b = 1 (Any pole open)

• 52b = 0 (All poles closed)

CIRCUIT BREAKER

52a

A

A

A

B

B

B C

C

C

52b

Breaker Position

Breaker Position

52a52a

52b

52b


Pole Discrepancy

Auxiliary contact arrangement at IPO breaker • Breaker position• Pole discrepancy

indication

CIRCUIT BREAKER

A

A

B

B

C

C

52a

Pole DiscrepancyFrom Breaker

52a

52a

A

B

C

52b

52b

52b

Breaker position with 52a (any pole closed)


Pole Discrepancy

Auxiliary contact arrangement at IPO breaker • Breaker position with 52a

and 52b• Pole discrepancy logic in IED


CIRCUIT BREAKER

A

A

B

B

C

C

52a - A

52a - B

52a - C

Pole Discrepency

ANDAND

IED Logic

OR

Pole Discrepancy

Auxiliary contact arrangement at IPO breaker • Breaker position with 52a/pole• Pole discrepancy logic in IED• Particularly suitable for SPT


Pole Discrepancy

Auxiliary contact arrangement at IPO breaker • Breaker position with 52a and 52b

per pole• Pole discrepancy logic in IED• Particularly suitable for SPT


Pole Discrepancy


Questions?

Breaker Failure Protection

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