Sel SEL-421 - Circuit Breaker Failure Initiation Dropout and Seal-In; Current-Supervised Single-Pole Retrip Logic

R.1.119
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Circuit Breaker Failure Protection
the RTA1 output for single-pole retrip without current supervision. Relay
Word bit RTSA1 (Breaker 1 Current Supervised A-Phase Retrip) asserts if
50FA1 is picked up.
Figure 1.76 Current-Supervised Single-Pole Retrip Logic
Circuit Breaker
Failure Initiation
Dropout and Seal-In
The SEL-421 circuit breaker failure protection features breaker failure
initiation extension and a breaker failure seal-in latch. The lower portion of
Figure 1.78 shows the dropout and seal-in logic.
Dropout Delay
Set timer BFIDO1 (Breaker Failure Initiate Dropout Delay—BK1) to stretch a
short pulsed circuit breaker failure initiation. Use this feature for protecting
dual circuit breakers when separate 86 BF lockout relays have differing
energizing times.
Seal-In Delay
Set timer BFISP1 (Breaker Failure Initiate Seal-In Delay—BK1) to qualify
extended circuit breaker failure initiation latch seal-in. When you set BFISP1
longer than BFIDO1 and the circuit breaker failure initiate is greater than the
difference of the two timers, the relay seals in the circuit breaker failure
extended initiation after the initiate signal deasserts until the BFIDO1 time
expires and all 50Fn elements deassert.
No Current/Residual
Current Circuit
Breaker Failure
Protection Logic
The SEL-421 has separate circuit breaker failure logic that operates on zero-
sequence current rather than phase current. Use this logic to detect a circuit
breaker failure and take appropriate action when a weak source drives the fault
or if the protected circuit breaker fails to trip during a high-resistance ground
fault. The residual current input to this logic is the 50R1 residual overcurrent
element (see Figure 1.77). Setting 50RP1 (Residual Current Pickup—BK1) is
the pickup threshold setting for the 50RP element.
Figure 1.77 No Current/Residual Current Circuit Breaker Failure Protection
Logic Diagram
BFIA1
BFIB1
BFIC1
RTA1
50FA1
RTSA1
Relay
Word
Bit
Relay
Word
Bits
SELOGIC
Settings
RTPU1
0
2 of 3
50R1
B1OPHA
B1OPHB
B1OPHC
BFI3P1
BFIN1
ENCBF1 := Y
NBF1
Relay
Word
Bits
Relay
Word
Bit
SELOGIC
Settings
Setting
NPU1
0