Sel SEL-421 - Current-Supervised Three-Pole Retrip Logic; Scheme 2 Single-Pole Circuit Breaker Failure Protection Logic

R.1.118
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Circuit Breaker Failure Protection
breaker failure tripping logic to cause a circuit breaker failure trip (see Circuit
Breaker Failure Trip Logic on page R.1.121). If the protected circuit breaker
successfully opens, 50FA1 drops out before timer SPBFPU1 expires and
Relay Word bit FBFA1 does not assert.
Figure 1.74 Scheme 2 Single-Pole Circuit Breaker Failure Protection Logic
Retrip Logic
Some single-pole circuit breakers have two separate trip coils per pole. All
three primary trip coils are energized if the line-relaying scheme asserts a
three-pole trip. If one or more of the primary trip coils fail, the local protection
should attempt a three-pole retrip.
Only one of the primary trip coils is energized if the line-relaying scheme
asserts a single-pole trip. The corresponding primary trip coil can fail
following the single-pole trip. You can decide whether to single-pole or
three-pole retrip following the unsuccessful single-pole trip. Attempt all local
retrips before the corresponding circuit breaker failure time delay (BFPUn and
SPBFPUn) on pickup timer expires.
Figure 1.75 illustrates the current-supervised three-pole retrip logic. Timer
RT3PPU1 (Breaker 1 Three-Pole Retrip Time Delay on Pickup Timer) begins
timing when at least two of the initiation Relay Word bits BFIA1, BFIB1, or
BFIC1 assert. The relay asserts RT3P1 (Three-Pole Retrip) when timer
RT3PPU1 times out. You can use just output RT3P1 for three-pole retrip
without current supervision. Relay Word bit RTS3P1 (Breaker 1 Current
Supervised Three-Pole Retrip) asserts immediately after timer RT3PPU1
expires, if one of the phase current level detectors is picked up.
Figure 1.75 Current-Supervised Three-Pole Retrip Logic
Figure 1.76 illustrates the current-supervised single-pole retrip logic. Timer
RTPU1 (Breaker 1 Retrip Time Delay on Pickup Timer) begins timing when
initiation Relay Word bit BFIA1 asserts. Relay Word bit RTA1 (Breaker 1 A-
Phase Retrip) asserts immediately after timer RTPU1 expires. You can use just
FBF1
BFIA1
BFIB1
50FA1
BFIC1
FBFA1
FBFC1
FBFB1
Relay
Word
Bit
Relay
Word
Bit
Relay
Word
Bits
SELOGIC
Settings
BFPU1
0
SPBFPU1
0
2 of 3
or
3 of 3
50FA1
50FB1
50FC1
BFIA1
RTS3P1
RT1
RT3P1
(Relay Word Bit)
BFIB1
BFIC1
RTSA1
RTSB1
RTSC1
Relay
Word
Bits
Relay
Word
Bit
SELOGIC
Settings
RT3PPU1
0
2 of 3