Date Code 20001006 Close and Reclose Logic 6-21
SEL-351 Instruction Manual
start timing on the first open interval. The SEL-351 is not yet in the reclose cycle state (79CY =
logical 0) at the instant of the first trip.
Then for any subsequent trip operations in the auto-reclose cycle, the SEL-351 is in the reclose
cycle state (79CY = logical 1) and the SEL-351 successfully initiates reclosing for each trip.
Because of factory setting 79RIS = 52A + 79CY, successful reclose initiation in the reclose cycle
state (79CY = logical 1) is not dependent on the circuit breaker status (52A). This allows
successful reclose initiation for the case of an instantaneous trip, but the circuit breaker status
indication is slow - the instantaneous trip (reclose initiation) occurs before the SEL-351 sees the
circuit breaker close.
If a flashover occurs in a circuit breaker tank during an open interval (circuit breaker open and the
SEL-351 calls for a trip), the SEL-351 goes immediately to lockout.
Additional Settings Example
The preceding settings example initiates open interval timing on rising edge of the TRIP Relay
Word bit. The following is an example of reclose initiation on the opening of the circuit breaker.
Presume input IN1 is connected to a 52a circuit breaker auxiliary contact (52A = IN1).
With setting:
79RI = !52A
the transition of the 52A Relay Word bit from logical 1 to logical 0 (breaker opening) initiates open
interval timing. Setting 79RI looks for a logical 0 to logical 1 transition, thus Relay Word bit 52A
is inverted in the 79RI setting [!52A = NOT(52A)].
The reclose initiate supervision setting 79RIS supervises setting 79RI. With settings:
79RI = !52A
79RIS = TRIP
the transition of the 52A Relay Word bit from logical 1 to logical 0 initiates open interval timing
only if the TRIP Relay Word bit is at logical 1 (TRIP = logical 1). Thus, the TRIP Relay Word
bit has to be asserted when the circuit breaker opens in order to initiate open interval timing. With
a long enough setting of the Minimum Trip Duration Timer (TDURD), the TRIP Relay Word bit
will still be asserted to logical 1 when the circuit breaker opens (see Figure 5.1 and Figure 5.2 in
Section 5: Trip and Target Logic).
If the TRIP Relay Word bit is at logical 0 (TRIP = logical 0) when the circuit breaker opens
(logical 1 to logical 0 transition), the relay goes to the Lockout State. This helps prevent reclose
initiation for circuit breaker openings caused by trips external to the relay.
If circuit breaker status indication (52A) is slow, additional setting change ULCL = 0 (unlatch
close; refer to Figure 6.1 and accompanying explanation) may need to be made when 79RI = !52A.
ULCL = 0 avoids going to lockout prematurely for an instantaneous trip after an auto-reclose by
not turning CLOSE off until the circuit breaker status indication tells the relay that the breaker is
closed. The circuit breaker anti-pump circuitry should take care of the TRIP and CLOSE being on
together for a short period of time.
Courtesy of NationalSwitchgear.com
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