Breaker Failure Protection

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Breaker Failure Protection 2

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 A 1 2 5 6 3 7 8 4 D _E C B

(3)

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

(4)

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 A 1 2 5 6 3 7 8 4 D _E C B

(5)

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

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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 C Fault X A 1 2 3 4 B 5

(7)

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 94 Relay Scheme #1 52a 52T 62X + dc - dc 62X + dc - dc 62BF 62 BF 62Y 86BF 50 Multiple 86BF Contacts 86 BF

(8)

Breaker Failure Logic

T 0 62X 62Y 50 86BF 52a 52a 86T 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

(9)

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}

(10)

Breaker-and-a-half Bus

Line 1 Line 2 50 2 50 1 50 3 Line 2 Relays Line 1 Relays 1 2 3 4 Bus L Bus R Breaker Failure 86 Relay Operations 1 Trip 2 and all Bus L

breakers.

Transfer trip Line 1

2 Trip 1 and 3.

Transfer trip lines 1 & 2.

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

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Ring Bus

Line 1 Relays Relays Line 2 50 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

(12)

Breaker Failure Logic

 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

*

T 0 62X 62Y 50 86BF 52a 52a 86T _62BF Options

*

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Breaker Failure Time Chart

Relay

Operate

Breaker Clearing Normal Clearing Time

50 Reset Margin Normal Clearing Failed Breaker 62X 62Y BFI 62BF Timer Setting 86 BF TFR TRIP Local Backup Clearing Remote Backup Clearing Normal Clearing

Local Backup BF Total Clearing

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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

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Breaker Failure Logic

 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

T R 62X 62Y 50BF Control Timer T 0 62BF _Torque Control 86BF Retrip

(16)

Breaker Failure Time Chart

Relay

Operate

Breaker Clearing Normal Clearing Time

50 Pickup Margin Normal Clearing Failed Breaker 62X 62Y BFI 62BF Timer Setting 86 BF TFR TRIP Local Backup Clearing Remote Backup Clearing Normal Clearing

Local Backup BF Total Clearing

Remote Backup BF Total Clearing

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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

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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

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Pole Discrepancy



Based on auxiliary 52a and/or 52b

contact positions

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Pole Discrepancy

 Auxiliary contact arrangement for

three pole gang operated breaker position indication

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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

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Pole Discrepancy

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 52a 52a 52b 52b

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Pole Discrepancy

arrangement at IPO breaker

• Breaker position • Pole discrepancy indication CIRCUIT BREAKER A A B B C C 52a Pole Discrepancy From Breaker 52a 52a A B C 52b 52b 52b

Breaker position with 52a (any pole closed)

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Pole Discrepancy

 Auxiliary contact arrangement at

IPO breaker

• Breaker position with 52a and 52b

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CIRCUIT BREAKER A A B B C C 52a - A 52a - B 52a - C Pole Discrepency AND AND IED Logic OR

Pole Discrepancy

 Auxiliary contact arrangement at

IPO breaker

• Breaker position with 52a/pole

• Pole discrepancy logic in IED

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Pole Discrepancy

 Auxiliary contact arrangement at IPO

breaker

• Breaker position with 52a and 52b per pole

• Pole discrepancy logic in IED

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