Schweitzer Engineering Laboratories SEL-421-4 - Figure 6.48 Timing Sequences for Circuit Breaker Failure Protection Scheme 2

6.165
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
Circuit Breaker Failure Application Examples
SPBFPU1 is an additional delay you can cascade to BFPU1 for single-phase
faults (see Figure 6.48). Set SPBFPU1 to extend breaker failure pickup time
delay as long as the total clearing time t
t
= 15 cycles.
SPBFPU1 := 5.000. SPT Breaker Failure Time Delay—BK1
(0.000–6000 cycles)
Retrip Time Delay
Scheme 2 provides retrip timers RT3PPU1 for multiphase faults and RTPU1 for
single-phase faults. Set the retrip following a single-pole trip to occur 3 cycles
after circuit breaker failure initiation.
RTPU1 := 3.000. Retrip Time Delay—BK1 (0.000–6000 cycles)
A three-pole retrip follows a three-pole trip. The relay should attempt to retrip the
protected circuit breaker before a circuit breaker failure trip asserts. Apply the
default setting for the three-pole retrip time delay on pickup.
RT3PPU1 := 3.000. Three-Pole Retrip Time Delay—BK1 (0.000–6000 cycles)
Figure 6.48 compares the complete timing sequence for single-pole versus three-
pole circuit breaker failure operations.
Circuit Breaker Failure Initiation
Scheme 2 does not use Relay Word bit BFI3P1 to initiate failure to interrupt fault
current circuit breaker failure protection.
BFI3P1 := NA. Three-Pole Breaker Failure Initiate—BK1 (SELOGIC Equation)
Figure 6.48 Timing Sequences for Circuit Breaker Failure Protection Scheme 2
3-Pole Event
(AB Fault)
BFIA1
50FA1
RT3PPU1
BFPU1
BFIB1
RT3P1
FBF1
1-Pole Event
(AG Fault)
50FA1
RTPU1
BFPU1
BFIA1
RTA1
FBF1
SPBFPU1