5-20 Applications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
Another implementation:
The 79RS bit or 79LO bit are asserted when the reclosing relay is in the reset state or lockout
state (the reclosing relay is not in the reclose cycle state).
Using SELOGIC Control Equations:
A3(1346)= 79RS+79LO (Output contact A3 should be configured as an "a" contact)
For either implementation the A3 output contact is wired to the load-tap-changer control. The
A3 output contact opens when the reclosing relay is in the reclosing cycle. This prevents load-
tap-changer operation.
Depending on the nature of the load-tap-changer control circuit, this application may be best
implemented by having an the SEL-251 Relay output contact connect to an interposing relay.
The interposing relay can then connect to the load-tap-changer control circuit.
EXTRA ALARM OUTPUT CONTACT
The A4 output contact can function as an extra ALARM output contact, depending on the
placement of jumper JMP3. With jumper JMP3 in the A4 position, the A4 output contact
operates per setting A4(2346). With jumper JMP3 in the ALARM position, the A4 output
contact operates with the ALARM output contact.
On Conventional Terminal Block Relays, all the output contacts can be configured as "a" or "b"
contacts with soldered wire jumpers JMP4 through JMP11 (each jumper has positions A and B).
ALARM output contacts are usually "b" contacts, so soldered wire jumper JMP5 (for A4 output
contact) should be in the B position for the A4 output contact to operate as an extra ALARM
output contact.
This extra ALARM contact can be used to notify backup protective relays of the primary relay
failure condition so that protection adjustments can be made. It can also be used for local
annunciation, SCADA input, trip supervision, etc.
BACKUP FEEDER RELAYS WITH A BUS RELAY
Use one SEL-251C Relay to backup the SEL-251 Relays installed on individual feeders. The
feeder relay ALARM contact can supervise a trip from the bus relay because backup is required
only when the feeder relay fails. Because of this supervision, the bus relay TRIP output contacts
can be set to operate simultaneously with feeder relay TRIP output contacts, both attempting to
trip the feeder circuit breaker.
Time delayed trips from the feeder relays (for feeder circuit breaker failures) and the bus relay
can trip the bus breaker. These time delayed trips are possible using the trip failure logic
available in the SEL-251 and SEL-251C Relays.
Using SELOGIC Control Equations (for SEL-251 and SEL-251C Relays):
A1(1234)= TF
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