Date Code 20111215 Reference Manual SEL-421 Relay
Section 2
R.Reference Manual
Auto-Reclosing and Synchronism Check
This section describes the operation of auto-reclose logic in the SEL-421
Relay. Also included in this section is a discussion of Voltage Check logic and
Synchronism Check logic that can be used with auto-reclosing, or applied
independently. This section covers the following topics:
➤ Auto-Reclosing on page R.2.2
➤ One-Circuit-Breaker Auto-Reclosing on page R.2.4
➤ Two-Circuit-Breaker Auto-Reclosing on page R.2.10
➤ Auto-Reclose Logic Diagrams on page R.2.27
➤ Manual Closing on page R.2.41
➤ Voltage Checks for Auto-Reclosing and Manual Closing on
page R.2.44
➤ Settings and Relay Word Bits for Auto-Reclosing and Manual
Closing on page R.2.46
➤ Synchronism Check on page R.2.50
The SEL-421 Relay auto-reclose and synchronism-check functions provide
complete control for single circuit breaker and two circuit breaker reclosing
schemes. The auto-reclose function accommodates both single-pole and three-
pole reclosing. You can set the SEL-421 for a total of two single-pole and four
three-pole reclose shots. The single-pole shots have a common dead time,
while the three-pole shots have individual dead times. You can designate the
leader and follower circuit breakers in a two circuit breaker configuration; the
SEL-421 recloser can dynamically change leader and follower designations
based on settings and operating conditions.
You can program the auto-reclose logic to perform one shot of high-speed
three-pole reclose. This high-speed three-pole shot replaces one of the four
delayed time three-pole shots. There is no difference between a shot of high-
speed three-pole reclose and a shot of delayed three-pole auto-reclose; simply
select the open interval time accordingly.
Two auto-reclose modes are available when using the SEL-421 to control two
circuit breakers:
➤ Combined two-breaker mode (setting E79 := Y)—both circuit
breakers must trip before any reclosing can occur.
➤ Independent two-breaker mode (setting E79 := Y1)—the
follower circuit breaker can trip and reclose even when the lead
breaker has not operated. This is useful on both ring bus and
breaker-and-a-half schemes, where the follower breaker is a tie
breaker that can be tripped by protection on either side.
For single circuit breaker applications, use setting E79 := Y.
NOTE: The SEL-421 voltage check
elements (for bus and line voltages)
may be used without the synchronism
check feature, however, for certain
voltage connections, some of the
synchronism check settings need to
be entered to ensure that the correct
voltages are used.
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