Sel 551 - Figure 3.20 Operation of SEL-351 Relay Shot Counter for Sequence Coordination with Line Recloser (Additional Setting Example 2)

3.37
Date Code 20110408 Instruction Manual SEL-551 Relay
Relay Elements and Logic
Reclosing Relay
To avoid this problem make the following sequence coordination setting:
79SEQ = 79RS * 51P1 * SH0
Refer to Figure 3.20.
If the SEL-551 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 3.18), the line recloser fast curve
operates to clear the fault. The SEL-551 also sees the fault. The phase time-
overcurrent pickup 51P1 asserts and then deasserts without tripping,
incrementing the relay shot counter from:
shot = 0 to shot = 1
Now the SEL-551 cannot operate on its faster-set phase time-overcurrent
element 51P1T because the shot counter is at shot = 1 (SH0 = logical 0):
TR = 51P1T * (SHO) + 51P2T = 51P1T * (logical 0) + 51P2T = 51P2T
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 3.20 Operation of SEL-351 Relay Shot Counter for Sequence Coordination With Line Recloser (Additional
Setting Example 2)
The line recloser continues to operate for the permanent fault beyond it, but
the SEL-551 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 * 51P1 * SH0 = 79RS * 51P1 * (logical 0) = logical 0
The shot counter stays at shot = 1.
Thus, if there is a coincident fault between the SEL-551 and the line recloser,
the SEL-551 will operate on 51P2T 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 3.20.
79SEQ = 79RS*51P1*SHO
51P1
Shot Counter
SH0
01
qw ew e r e
r