Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.107 Scheme 2 Single-Pole Circuit Breaker Failure Protection Logic; Figure 5.108 Scheme Y2 Single-Pole Circuit Breaker Failure Protection Logic

5.150
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Circuit Breaker Failure Protection
Failure to Interrupt Fault Current: Scheme Y2 (Setting EBFL = Y2)
Single-Pole Circuit Breaker Failure Protection Logic
The logic shown in Figure 5.108 applies to single-pole breaker configurations.
Scheme Y2 is similar to Scheme 2, but the current check (50FA1) is now part of
the Breaker Failure initiate timer (BFPU1) and Retrip Time delay (RTPU1) in
addition to the Breaker Failure initiate settings (BFI3P1 or BFIA1).
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 sin-
gle-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 correspond-
ing circuit breaker failure time delay (BFPUn and SPBFPUn) on pickup timer
expires.
Retrip Scheme 2 Three Pole (Setting EBFL = 2)
Figure 5.109 illustrates the current-supervised three-pole retrip logic (EBFL = 2).
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 5.107 Scheme 2 Single-Pole Circuit Breaker Failure Protection Logic
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
Figure 5.108 Scheme Y2 Single-Pole Circuit Breaker Failure Protection Logic
FBF1
BFIA1
BFIB1
50FA1
BFIC1
FBFA1
FBFC1
FBFB1
Relay
Word
Bit
Relay
Word
Bits
SELOGIC
Settings
BFPU1
0
SPBFPU1
0
2 of 3
or
3 of 3