6.29
Date Code 20080213 Instruction Manual SEL-351A Relay
Close and Reclose Logic
Reclosing Relay
To avoid this problem, make the following sequence coordination setting:
79SEQ = 79RS * 51P * SH0
Refer to Figure 6.10.
If the SEL-351A 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 IF in Figure 6.8), the line recloser fast curve
operates to clear the fault. The SEL-351A 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-351A 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
q Fault occurs beyond line recloser; w fault cleared by line recloser fast curve; e line recloser recloses into fault; r fault
cleared by line recloser slow curve.
Figure 6.10 Operation of SEL-351A 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-351A 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-351A and the line
recloser, the SEL-351A 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 on page 6.1.
9SEQ = 79RS * 51P1 * SHO
51P1
Shot Counter
SH0
01
qw ew e r e
r
Courtesy of NationalSwitchgear.com
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