Date Code 20010625
Close and Reclose Logic
6-29
SEL-311L Instruction Manual
deassert, thus continuing the sequencing of the shot counter to shot = 3, etc. The T50PT element
cannot cause a trip because shot
≥
2, and SH0 and SH1 both are deasserted to logical 0.
Note:
Sequence coordination can increment the shot counter beyond last shot in this example
(last shot = 2 in this factory setting example) but no further than shot = 4.
The following Example 2 limits sequence coordination shot counter incrementing.
The shot counter returns to shot = 0 after the reset timer (loaded with reset time 79RSD) times
out.
Additional Settings Example 2
Review preceding Example 1.
Assume that the line recloser in Figure 6.7 is set to operate twice on the fast curve and then twice
on the slow curve for faults beyond the line recloser.
Assume that the SEL-311L Relay is set to operate once on T50PT and then twice on T51PT for
faults between the SEL-311L Relay and the line recloser. This results in the following trip
setting:
TR
= T50PT * (SHO) + T51PT
This requires that two open interval settings be made (see Table 6.2 and Figure 6.6). This
corresponds to the last shot being:
last shot = 2
If the sequence coordination setting is:
79SEQ
= 79RS * T50P
and there is a permanent fault beyond the line recloser, the shot counter of the SEL-311L Relay
will increment all the way to shot = 4 (see Figure 6.8). If there is a coincident fault between the
SEL-311L Relay and the line recloser, the SEL-311L Relay will trip and go to the Lockout State.
Any time the shot counter is at a value equal to or greater than last shot and the relay trips, it
goes to the Lockout State.
To avoid this problem, make the following sequence coordination setting:
79SEQ
= 79RS * T50P * SH0
If the SEL-311L Relay is in the Reset State (79RS = logical 0) with the shot counter reset (shot =
0; SH0 = logical 1) and then a permanent fault beyond the line recloser occurs (fault current I
F
in
Figure 6.7), the line recloser fast curve operates to clear the fault. The SEL-311L Relay also sees
the fault. The phase time-overcurrent pickup T50P asserts and then deasserts without tripping,
incrementing the relay shot counter from:
shot = 0 to shot = 1
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