Schweitzer Engineering Laboratories SEL-421-4 - Page 495

6.159
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
Circuit Breaker Failure Application Examples
Residual Current Circuit Breaker Failure Time Delay
Setting NPU1 is the time delay on pickup before the relay asserts a low current
circuit breaker failure trip for Circuit Breaker BK1. You can set this delay greater
than BFPU1; a high-resistance ground fault is not as much a threat to power sys-
tem transient stability as is a phase fault, because synchronizing power still flows
through the two unfaulted phases.
NPU1 := 12.000. No Current Breaker Failure Delay—BK1 (0.000–6000
cycles)
Residual Current Circuit Breaker Failure Initiation
This particular application uses the residual current circuit breaker failure scheme
only to detect when the circuit breaker fails to trip during high-resistance ground
faults. Set SEL
OGIC control equation BFIN1 (No Current Breaker Failure Initi-
ate) to NA.
If you want to apply this scheme for no current conditions (e.g., weak source),
assign the 52A contact from Circuit Breaker BK1 (52AA1) to the SEL
OGIC con-
trol equation BFIN1 (No Current Breaker Failure Initiate).
BFIN1 := NA. No Current Breaker Failure Initiate—BK1 (SELOGIC Equation)
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)
Circuit Breaker Failure Protection Trip Logic
Circuit Breaker 1 Failure Trip Equation
The SEL-421 has dedicated circuit breaker failure trip logic. Set SELOGIC con-
trol equation BFTR1 (Breaker Failure Trip—BK1) to assert for either Circuit
Breaker BK1 circuit breaker failure trip or Circuit Breaker BK1 residual current
circuit breaker failure trip. When this SEL
OGIC control equation asserts, the relay
sets Relay Word bit BFTRIP1 to logical 1 until BFTR1 deasserts, the TDUR3D
timer times out, and an unlatch or reset condition is active.
BFTR1 := FBF1 OR NBF1. Breaker Failure Trip—BK1 (SELOGIC Equation)
Unlatch Circuit Breaker 1 Failure Trip Equation
Use SELOGIC control equation BFULTR1 (Breaker Failure Unlatch Trip—BK1)
to define the conditions that unlatch the control outputs that assert during a circuit
breaker failure trip. BFULTR1 unlatches the circuit breaker trip condition