Schweitzer Engineering Laboratories SEL-311L, Instruction Manual, Page: 244 / 734

6-26 Close and Reclose Logic Date Code 20010625
SEL-311L Instruction Manual
Sequence Coordination Setting (79SEQ)
The sequence coordination setting 79SEQ keeps the relay in step with a downstream tapped load
line recloser in a sequence coordination scheme, which prevents overreaching for faults beyond
the 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 (SEL
OGIC
control equation setting 52A = logical 1, effectively)
The sequence coordination setting 79SEQ is usually set with tapped load overcurrent element
pickups. If the above two conditions are both true, and a set overcurrent 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 6.7) has
operated to clear a fault. Incrementing the shot counter keeps the SEL-311L Relay “in step”
with the downstream device, as is shown in the following
Additional Settings Example 1 and
Additional Settings Example 2 .
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.
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.
Factory Settings Example
Sequence coordination is not enabled in the factory settings:
79SEQ = 0
Additional Settings Example 1
With sequence coordination setting:
79SEQ = 79RS * T50P
sequence coordination is operable only when the relay is in the Reset State (79RS = logical 1).
Refer to Figure 6.7 and Figure 6.8.