2-18
Specifications
Date Code 20000421
SEL-251, -2, -3 Instruction Manual
If a trip occurs and no reclose cancel condition exists, the relay starts to time on the appropriate
open interval (if any remain) when the trip drops out and 52A input deasserts. When the open
interval timer expires, the shot counter is incremented and the CLOSE output contact asserts. A
close failure timer limits the duration of CLOSE output contact assertion in case 52A does not
assert. See
Functional Specifications
for a description of close failure timer operation. If the
close failure timer is not used, the CLOSE output contact remains asserted until 52A asserts.
If the circuit breaker recloses successfully, the reset interval timer starts. Assertion of any
element in Relay Word row R1 indicates an overcurrent condition. Detection of an overcurrent
condition reinitializes the reset interval timer and inhibits it from timing. When the overcurrent
conditions drop out, the reset interval timer starts. When this timer expires, the reclosing relay
goes to the reset state (
79RS
= 1) and shot = 0.
Any of the six programmable inputs can be set as a reclose enable (RE) input. If the RE input is
deenergized (RE = 0), the relay goes to lockout (
79LO
= 1). When the reclose enable input is
deenergized, the CLOSE output contact cannot automatically assert via the reclosing relay.
If no input is assigned to the RE input, RE = 1 internally (reclosing is always enabled). If a
scheme is set up this way, you can defeat automatic reclosing by setting the first open interval to
zero (79OI1=0).
One input must be designated either 52A, !52A, 52AR, or !52AR. Otherwise, automatic reclos-
ing and other close operations using the CLOSE output contact are unavailable (CLOSE
Command, Direct Close).
The number of non-zero open interval time periods determines available reclosing shots (four
shots maximum). The Relay Word bit
79SH
can assert (
79SH
= 1) for different shots, 0 through
4. For example, if you only want
79SH
to assert for shots 0 and 1, enter the following setting:
M79SH = 11000
79SH
can be used to supervise overcurrent elements and reclose cancel conditions.
Reclosing relay timing accuracy is
±
1 cycle.
Reclose Cancel Conditions
The internal reclose cancel variable RC(1246) can be set to equal any OR-combination of
elements in Relay Word rows R1, R2, R4, and R6. Reclosing is also canceled if:
An input assigned to RE (reclose enable) is not asserted,
An input assigned to DT (direct trip) is asserted,
The CF (close fail) condition occurs, or
The OPEN command is enabled and executed.