4.145
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
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-751 sees the circuit breaker close.
If a flashover occurs in a circuit breaker tank during an open interval (circuit
breaker open and the SEL-751 calls for a trip), the SEL-751 goes immediately
to lockout.
EXAMPLE 4.20 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 IN101 is connected to a 52a circuit breaker auxiliary contact
(52A := IN101).
With setting:
79RI := NOT 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.
The reclose initiate supervision setting 79RIS supervises setting 79RI. With
settings:
79RI := NOT 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 to initiate open interval timing. With a long enough
setting of the Minimum Trip Duration Timer (TDURD), the TRIP Relay Word
bit still asserts to logical 1 when the circuit breaker opens (see Figure 4.44).
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 4.80 and accompanying
explanation) may need to be made when 79RI := NOT 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.
Other Settings Considerations
In Example 4.20, the preceding additional setting example, the reclose initiate
setting (79RI) includes input IN101, which is connected to a 52a breaker auxil-
iary contact (52A := IN101).
79RI := NOT 52A
If a 52b breaker auxiliary contact is connected to input IN101 (52A := NOT
IN101), the reclose initiate setting (79RI) remains the same.
If no reclose initiate supervision is desired, make the following setting:
79RIS := 1 (numeral 1)
Setting 79RIS := logical 1 at all times. Any time setting 79R1 detects a
logical 0 to logical 1 transition, the relay initiates open interval timing (unless
prevented by other means).
If the following setting is made:
79RI := 0 (numeral 0)
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