Schweitzer Engineering Laboratories SEL-421-4 - Page 503

6.167
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
Circuit Breaker Failure Application Examples
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 a Circuit Breaker
BK1 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
TDUR1D timer times out, and an unlatch or reset condition is active.
BFTR1 := FBF1. Breaker Failure Trip—BK1 (SELOGIC Equation)
Unlatch Circuit Breaker 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
BFTRIP1 (Breaker Failure Trip for Circuit Breaker 1). Assign a control input that
is energized externally to signal the relay when the circuit breaker failure trip
clears the fault successfully.
BFULTR1 := IN104. Breaker Failure Unlatch Trip—BK1 (SELOGIC Equation)
Use the same input signal to unlatch the circuit breaker failure trip on Circuit
Breaker BK2.
Control Outputs
Use SELOGIC control equations to assign the control outputs for tripping and
retripping Circuit Breaker BK1 and Circuit Breaker BK2 and circuit breaker fail-
ure tripping. These output assignments are for the SEL-421 with an additional
INT6 I/O interface board (see I/O Interface Boards on page 2.13).
NOTE: The symbol  indicates A, B,
and C for A-Phase, B-Phase, or
C-phase of the power system.
Assign the trip outputs to the hybrid (high current interrupting) control outputs.
Use the high current interrupting control outputs for the retrip signal (RT1)
because these outputs can interrupt large circuit breaker coil currents. There is no
TDUR3D (3PT Minimum Trip Duration Time Delay) for RT1; the RT1 signal
can drop out while there is current flowing through the trip coil, if the auxiliary
circuit breaker contacts have not yet opened.
OUT101 := TPA1.
OUT102 := TPB1.
OUT103 := TPC1.
OUT107 := BFTRIP1.
OUT201 := TPA2.
OUT202 := TPB2.
OUT203 := TPC2.
OUT204 := RTA1.
OUT205 := RTB1.
OUT206 := RTC1.
OUT207 := RTA2.