6.160
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
Circuit Breaker Failure Application Examples
BFTRIP1 (Breaker Failure Trip for Circuit Breaker BK1). 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)
Control Outputs
Use SELOGIC control equations to assign control outputs for tripping Circuit
Breaker BK1, retripping Circuit Breaker BK1, and circuit breaker failure trip-
ping. Figure 6.44 shows dc connections for the circuit breaker failure trip and cir-
cuit breaker trip/retrip.
Use the main board high current interrupting control output for the retrip signal
(RT1) because this output can interrupt large circuit breaker coil currents. There
is no TDUR3D (3PT Minimum Trip Duration Time Delay) for RT1; the RT1 sig-
nal can drop out while there is current flowing through the trip coil, if the auxil-
iary circuit breaker contacts have not yet opened.
OUT101 := 3PT.
OUT103 := RT1.
OUT107 := BFTRIP1.
Example Completed
This completes the application example that describes setting of the SEL-421 for
circuit breaker failure protection. Analyze your particular power system to deter-
mine the appropriate settings for your application.
Relay Settings
Table 6.42 lists all protective relay settings applied for this example.
Figure 6.44 Circuit Breaker Failure Trip and Circuit Breaker Trip DC
Connections
86-1
86-1
86-1
BFTRIP1
(OUT107)
DC1 (—)
DC2 (—)
DC2 (+)
DC1 (+)
TC-1
3PT
(OUT101)
TRIP COIL #2
TRIP COIL #1
CBF LOCKOUT
TC-2
52AA1
RT1
(OUT103)
DC3 (—)
DC3 (+)
52AA1
Table 6.42 Settings for Circuit Breaker Failure Example 1 (Sheet 1 of 2)
Setting Prompt Entry
Relay Configuration (Group)
EBFL1 Breaker 1 Failure Logic (N, 1, 2, Y1, Y2) 1
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