6.89
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
EHV Parallel 230 kV Underground Cables Example
Application Summary
This particular example is for a single circuit breaker, three-pole tripping applica-
tion with the following functions:
➤ POTT (permissive overreaching transfer trip) scheme
➤ Three zones of phase (mho) and ground (quadrilateral) distance
protection
➢ Zone 1—forward-looking, provides instantaneous
underreaching protection
➢ Zone 2—forward-looking, provides communications-assisted
and time-delayed tripping
➢ Zone 3—reverse-looking, prevents unwanted tripping during
current reversals
➤ Two levels of negative-sequence directional overcurrent protection
➢ Level 2—forward-looking, provides communications-assisted
high-speed tripping
➢ Level 3—reverse-looking, prevents unwanted tripping during
current reversals
➤ Inverse-time directional negative-sequence overcurrent backup
protection
➤ 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 := LEWISTON -- 230 kV. Station Identifier (40 characters)
RID := SEL-421 Relay. Relay Identifier (40 characters)
Configure the SEL-421 for the one circuit breaker that this particular application
uses:
NUMBK := 1. Number of Breakers in Scheme (1, 2)
BID1 := Circuit Breaker 1. Breaker 1 Identifier (40 characters)
Set the relay for nominal frequency and phase rotation.
NFREQ := 60. Nominal System Frequency (50, 60 Hz)
PHROT := ABC. System Phase Rotation (ABC, ACB)
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