4.150
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
EXAMPLE 4.29 Additional Settings Example 2
If the block reset timing setting is:
79BRS := 51P1P OR 51G1P
then reset timing is blocked if time-overcurrent pickup 51P1P or 51G1P is
picked up, regardless of the reclosing relay state.
Sequence Coordination Setting (79SEQ)
The sequence coordination setting 79SEQ keeps the relay in step with a down-
stream line recloser in a sequence coordination scheme, which prevents over-
reaching SEL-751 overcurrent elements from tripping for faults beyond the
line recloser. This is accomplished by incrementing the shot counter and
supervising overcurrent elements with resultant shot counter elements.
In order for the sequence coordination setting 79SEQ to increment the shot
counter, both the following conditions must be true:
➤ No trip present (Relay Word bit TRIP = logical 0)
➤ Circuit breaker closed (SELOGIC control equation setting
52A = logical 1, effectively)
The sequence coordination setting 79SEQ is usually set with some overcurrent
element pickups. If the previous two conditions are both true, and a set over-
current element pickup asserts for at least 1.25 cycles and then deasserts, the
shot counter increments by one count. This assertion/deassertion indicates that
a downstream device (e.g., line recloser—see Figure 4.87) has operated to
clear a fault. Incrementing the shot counter keeps the SEL-751 “in step” with
the downstream device, as is shown in Additional Settings Example 1 on
page 4.150 and Additional Settings Example 2 on page 4.152.
Every time a sequence coordination operation occurs, the shot counter is
incremented, and the reset timer is loaded up with reset time 79RSD.
Sequence coordination can increment the shot counter beyond last shot, but no
further than shot = 4. The shot counter returns to shot = 0 after the reset timer
times out. Reset timing is subject to SEL
OGIC control equation setting 79BRS
(see Block Reset Timing Setting (79BRS) on page 4.149).
Sequence coordination operation does not change the reclosing relay state. For
example, if the relay is in the Reset State and there is a sequence coordination
operation, it remains in the Reset State.
EXAMPLE 4.30 Factory Settings Example
Sequence coordination is not enabled in the factory settings:
79SEQ := 0
EXAMPLE 4.31 Additional Settings Example 1
With sequence coordination setting:
79SEQ := 79RS AND 51P1P
sequence coordination is operable only when the relay is in the Reset State
(79RS = logical 1). Refer to Figure 4.87 and Figure 4.88.
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