6.47
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Direct Tripping
Direct tripping is faster because the SEL-421 Relays at Station S do not have to
wait for the circuit breakers at Station R to single-pole trip first; that is, the
SEL-421 Relays at Station R single-pole direct transfer trip the SEL-421 Relays
at Station S during crossing country faults beyond the reach of Zone 1 ground-
distance protection at Station S.
Transmit Equations
TMB3A := TPA AND NOT 3PT. Transmit MIRRORED BITS 3A (SELOGIC Equa-
tion)
TMB4A := TPB AND NOT 3PT. Transmit MIRRORED BITS 4A (SELOGIC Equa-
tion)
TMB5A := TPC AND NOT 3PT. Transmit MIRRORED BITS 5A (SELOGIC Equa-
tion)
Receive Equations
DTA := RMB3A. Direct Transfer Trip A-Phase (SELOGIC Equation)
DTB := RMB4A. Direct Transfer Trip B-Phase (SELOGIC Equation)
DTC := RMB5A. Direct Transfer Trip C-Phase (SELOGIC Equation)
Example Completed
This completes the application example that describes how to set the SEL-421 for
communications-assisted protection of 500 kV parallel overhead transmission
lines with zero-sequence mutual coupling. Analyze your particular power system
to determine the appropriate settings for your application.
Relay Settings
Table 6.13 lists all protective relay settings for this example. Settings used in this
example appear in boldface type.
Table 6.13 Settings for 500 kV Parallel TX Example (Sheet 1 of 7)
Setting Prompt Entry
General Global (Global)
SID Station Identifier (40 characters) MOSCOW - 500 kV
RID Relay Identifier (40 characters) SEL-421 Relay
NUMBK Number of Breakers in Scheme (1, 2) 2
BID1 Breaker 1 Identifier (40 characters) Circuit Breaker 1
BID2 Breaker 2 Identifier (40 characters) Circuit Breaker 2
NFREQ Nominal System Frequency (50, 60 Hz) 60
PHROT System Phase Rotation (ABC, ACB) ABC
DATE_F Date Format (MDY, YMD, DMY) MDY
FAULT Fault Condition (SEL
OGIC Equation) 50P1 OR 51S1 OR
Z2P OR Z2G OR
Z3P OR Z3G
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