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6.142
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
Autoreclose and Synchronism-Check Example
Autoreclose Application
Apply the SEL-421 for one shot of single-pole reclosing and one shot of three-
pole reclosing.
Select the recloser mode with the enable setting E79 := Y or Y1, and set E3PR1
and E3PR2 to logical 1.
Modes of Operation
The SEL-421 autoreclose logic operates in one of two modes at all times:
➤
Single-pole mode (SPAR)
➤
Three-pole mode (3PAR)
Single-pole trips initiate single-pole reclosing. For this application example, if
the single-pole reclose is unsuccessful, the second trip is a three-pole trip. Three-
pole trips initiate three-pole reclosing. If a single-pole autoreclose cycle is in
progress and the relay receives an initiation for three-pole reclosing, the relay
immediately starts a three-pole autoreclose cycle.
Select the recloser mode with the three-pole enable settings and the single-pole
enable settings E3PR1, E3PR2, ESPR1, and ESPR2.
Autoreclose Sequence
The relay performs one shot of reclosing for both single-pole and three-pole auto-
matic reclosing.
When E79 := Y, the leader circuit breaker (CB1) recloses if the line is dead and
Bus 1 is hot. If the leader successfully recloses, the follower circuit breaker
(CB2) also attempts a reclose if the synchronism check is successful. CB2 can
also close if the line is dead and Bus 2 is hot if CB1 is out of service. A similar
SEL-421 installation would protect Line 2, and provide autoreclose capabilities.
When E79 := Y1, if CB2 trips from the Line 2 protection (not shown), the
SEL-421 on Line 1 would attempt to reclose CB2. This configuration would typ-
ically employ a hot bus check.
Open interval timing does not begin until the faulted phase(s) is opened.
If another trip occurs while the single-pole autoreclose cycle is in progress the
relay trips the other two poles.
The autoreclose logic resets after the reclaim timer (SPRCD or 3PRCD) expires.
Dynamic Determination of the Leader Circuit Breaker
If Circuit Breaker 1 (the leader breaker) is out of service, the leader settings are
automatically routed to Circuit Breaker 2. Circuit Breaker 2 operates as the
leader circuit breaker when Circuit Breaker 1 is out of service. When Circuit
Breaker 2 is the leader, this circuit breaker can single-pole reclose.
Summary of Contents for SEL-421-4
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