6-32
Close and Reclose Logic
Date Code 20001006
SEL-351 Instruction Manual
The SEL-351 Relay also sees the fault. The phase time-overcurrent pickup 51P asserts and then
deasserts without tripping, incrementing the relay shot counter from:
shot = 0 to shot = 1
Now the SEL-351 Relay cannot operate on its faster-set phase time-overcurrent element 51PT
because the shot counter is at shot = 1 (SH0 = logical 0):
TR
= 51PT * (SHO) + 51AT + 51BT + 51CT
= 51PT * (logical 0) + 51AT + 51BT + 51CT
= 51AT + 51BT + 51CT
Figure 6.10: Operation of SEL-351 Relay Shot Counter for Sequence Coordination With
Line Recloser (Additional Settings Example 2)
The line recloser continues to operate for the permanent fault beyond it, but the SEL-351 Relay
shot counter does not continue to increment. Sequence coordination setting 79SEQ is effectively
disabled by the shot counter incrementing from shot = 0 to shot = 1.
79SEQ
= 79RS * 51P * SH0 = 79RS * 51P * (logical 0) = logical 0
The shot counter stays at shot = 1.
Thus, if there is a coincident fault between the SEL-351 Relay and the line recloser, the SEL-351
Relay will operate on 51AT, 51BT, or 51CT and then reclose once, instead of going straight to the
Lockout State (shot = 1 < last shot = 2).
As stated earlier, the reset time setting 79RSD takes the shot counter back to shot = 0 after a
sequence coordination operation increments the shot counter. Make sure that reset time setting
79RSD is set long enough to maintain the shot counter at shot = 1 as shown in Figure 6.10.
Reclose Supervision Setting (79CLS)
See
Reclose Supervision Logic
earlier in this section.
Содержание SEL-351
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