Schweitzer Engineering Laboratories SEL-421-4 - Page 502

6.166
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
Circuit Breaker Failure Application Examples
Assign the protection elements to Relay Word bits BFIA1, BFIB1, and BFIC1 to
initiate single-pole trip circuit breaker failure protection for Circuit Breaker BK1.
For a complete description of circuit breaker failure initiation, see Circuit
Breaker Failure Protection on page 5.146. This application example uses the
POTT tripping scheme, step-distance backup protection, and SOTF protection.
BFIA1 := BFIAT1 OR TPA1. A-Phase Breaker Failure Initiate—BK1
(SEL
OGIC Equation)
BFIB1 := BFIBT1 OR TPB1. B-Phase Breaker Failure Initiate—BK1
(SEL
OGIC Equation)
BFIC1 := BFICT1 OR TPC1. C-Phase Breaker Failure Initiate—BK1
(SEL
OGIC Equation)
Relay Word bits BFIAT1, BFIBT1, and BFICT1 (Circuit Breaker 1 Latched Sin-
gle-Pole Circuit Breaker Failure Initiation) latch the BFIA1, BFIB1, and BFIC1
inputs to the circuit breaker failure protection.
Circuit Breaker Failure Protection Initiation Dropout Delay
Set the circuit breaker failure initiate time delay on dropout to stretch a short
pulsed circuit breaker failure initiation. Enable this feature for this application
example because you are protecting dual circuit breakers.
BFIDO1 := 3.000. Breaker Failure Initiate Dropout Delay—BK1
(0.000–1000 cycles)
Circuit Breaker Failure Protection Initiation Seal-In Delay
Set the circuit breaker failure initiate time delay on pickup for the latch logic to
qualify extended circuit breaker failure initiation latch seal-in.
BFISP1 := 4.000. Breaker Failure Initiate Seal-In Delay—BK1
(0.000–1000 cycles)
For these BFIDO1 and BFISP1 settings, if the circuit breaker failure initiate is 1
cycle or more, the relay seals in the circuit breaker failure extended initiation
after the initiate signal deasserts until the BFIDO1 time (3 cycles) expires and all
50F1 elements deassert.
Residual Current Circuit Breaker Failure Protection
Disable residual current circuit breaker failure protection for Circuit Breaker
BK1 because a strong source drives this terminal.
ENCBF1 := N. No Current/Residual Current Logic—BK1 (Y, N)
Load Current Circuit Breaker Failure Protection
Disable load current circuit breaker failure protection for Circuit Breaker BK1.
ELCBF1 := N. Load Current Breaker Failure Logic—BK1 (Y, N)
Flashover Circuit Breaker Failure Protection
Disable flashover current circuit breaker failure protection for Circuit Breaker
BK1.
EFOBF1 := N. Flashover Breaker Failure Logic—BK1 (Y, N)