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6.154
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
Circuit Breaker Failure Application Examples
Scheme 2
Relay Word bit FBF1 (Breaker 1 Breaker Failure) asserts for these conditions:
➤
A
single phase-to-ground fault occurs
: FBF1 asserts when time delay
on pickup timers BFPU1 (Breaker Failure Time Delay—BK1)
followed by SPBFPU1 (SPT Breaker Failure Time Delay—BK1)
expire. The corresponding 50FP
1 element and only one single-
phase breaker failure initiation (for example, BFIA1) are asserted.
➤
A
multiphase fault occurs
: FBF1 asserts when time delay on pickup
timer BFPU1 (Breaker Failure Time Delay—BK1) expires. The
corresponding 50F
1 elements and at least two single-phase breaker
failure initiations (for example, BFIA1 and BFIB1) are asserted.
Timing Sequence
and
illustrate the timing sequence for circuit breaker fail-
ure schemes.
Scheme 1
Scheme 1 follows
.
Scheme 2
Scheme 2 uses both timing sequences in
and
, depending
on the fault type (multiphase fault and single-phase fault, respectively).
Figure 6.40
Scheme 1 All Faults and Scheme 2 Multiphase Fault Timing Diagram
50F
φ
n Element
Asserts
Transfer
Trip
Asserts
BF Trip
Outputs
Assert
BF Timer Delay (BFPU)
Communications Channel Time
Absolute Maximum Fault Clearing Time
t
Local Backup
Breakers Trip
Time
Remote Breakers
Trip Time
Protective Relay
Operate Time
Maximum Breaker
Operating Time
50F
φ
n
Dropout Time
Safety Margin
Time
Fault Occurs
Trip Asserts
Normal
Operation
Breaker
Failure
Operation
Auxiliary Breaker Failure
Relay Operate Time
Summary of Contents for SEL-421-4
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