6.56
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
Application Summary
This particular example is for a single circuit breaker, three-pole tripping applica-
tion with the following functions:
➤ DCB (directional comparison blocking) trip scheme
➤ Three zones of mho phase and ground-distance protection
➢ Zone 1, forward-looking, instantaneous underreaching protection
➢ Zone 2, forward-looking, communications-assisted high-speed
tripping and time-delayed tripping
➢ Zone 3, reverse-looking, starting element
➤ Two levels of zero-sequence directional overcurrent protection
➢ Level 2, forward-looking, communications-assisted high-speed
tripping
➢ Level 3, reverse-looking, starting element
➤ Inverse-time directional zero-sequence overcurrent backup
protection
➤ Load-encroachment logic: prevents unwanted tripping during heavy
load conditions
➤ SOTF protection: fast tripping when the circuit breaker closes
Relay settings that are not mentioned in this example do not apply to this applica-
tion example.
Global Settings
General Global Settings
The SEL-421 has settings for identification. These settings allow you to identify
the following:
➤ Station (SID)
➤ Relay (RID)
➤ Circuit Breaker 1 (BID1)
You can enter as many as 40 characters per identification setting.
SID := KELLOG - 345 kV. Station Identifier (40 characters)
RID := SEL-421 Relay. Relay Identifier (40 characters)
Configure the SEL-421 for one circuit breaker.
NUMBK := 1. Number of Breakers in Scheme (1, 2)
BID1 := Circuit Breaker 1. Breaker 1 Identifier (40 characters)
You can select both nominal frequency and phase rotation for the relay.
NFREQ := 60. Nominal System Frequency (50, 60 Hz)
PHROT := ABC. System Phase Rotation (ABC, ACB)
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