Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.101 Trip a Unlatch Logic; Figure 5.102 Trip During Open Pole; Circuit Breaker Failure Protection

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SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Circuit Breaker Failure Protection
Circuit Breaker Failure Protection
Use the SEL-421 to provide circuit breaker failure protection for as many as two
circuit breakers. The circuit breaker failure protection logic includes the follow-
ing schemes:
➤ Failure to interrupt fault current for phase currents
➤ Failure to interrupt load current
➤ No current/residual current circuit breaker failure protection
➤ Flashover protection while the circuit breaker is open
All schemes can incorporate single-pole and three-pole retrip. Single-pole and
three-pole initiations are available for circuit breaker failure, including extended
breaker failure initiation. The circuit breaker failure logic also includes breaker
failure trip latching logic.
The failure-to-interrupt-fault-current logic includes two schemes; both are suit-
able for three-pole or single-pole tripping applications. Scheme 1 is basic circuit
breaker failure that is useful for most applications. Scheme 2 allows you to have
Figure 5.101 Trip A Unlatch Logic
Figure 5.102 Trip During Open Pole
0
1
CYC
3PT
LOPHA
TULO := 1
TULO := 2
52AA1
52AA2
TULO := 3
LOPHA
LOPHB
LOPHC
ULTRA
TULO := 4 Do not run this logic. ULTRA=0, ULTRB=0, ULTRC=0
Relay
Word
Bit
Relay
Word
Bit
Relay
Word
Bit
Relay
Word
Bits
Setting
Setting
Setting
NUMBK=2
1/8 CYC
TOPD
0
1/8
CYC
Relay
Word
Bit
Relay
Word
Bits
TOP
SPT
TPA
TPB
TPC
E3PT
SELOGIC
Setting