Schweitzer Engineering Laboratories SEL-351A, Руководство пользователя

Страница: 226 / 666

6.28
SEL-351A Relay Instruction Manual
Date Code 20080213
Close and Reclose Logic
Reclosing Relay
If the SEL-351A is in the Reset State (79RS = 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
When the line recloser recloses its circuit breaker, the line recloser fast curve
operates again to clear the fault. The SEL-351A also sees the fault again. The
phase time-overcurrent pickup 51P asserts and then deasserts without tripping,
incrementing the relay shot counter from:
shot = 1 to shot = 2
The line recloser fast curve is now disabled after operating twice. When the
line recloser recloses its circuit breaker, the line recloser slow curve operates
to clear the fault. The relay does not operate on its faster-set phase time-
overcurrent element 51PT (51PT is “below” the line recloser slow curve)
because the shot counter is now at shot = 2. For this sequence coordination
scheme, the SEL
OGIC
control equation trip equation is:
TR = 51PT * (SH0 + SH1) + 51AT + 51BT + 51CT
With the shot counter at shot = 2, Relay Word bits SH0 (shot = 0) and SH1
(shot = 1) are both deasserted to logical 0. This keeps the 51PT phase time-
overcurrent element from tripping. The 51PT phase time-overcurrent element
is still operative, and its pickup (51P) can still assert and then deassert, thus
continuing the sequencing of the shot counter to shot = 3, etc. The 51PT phase
time-overcurrent element cannot cause a trip because shot
≥
2, and SH0 and
SH1 both are deasserted to logical 0.
The shot counter returns to shot = 0 after the reset timer (loaded with reset
time 79RSD) times out.
Additional Settings Example 2
Review preceding Additional Settings Example 1 on page 6.26 .
Assume that the line recloser in Figure 6.8 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-351A is set to operate once on 51PT and then twice on
51AT, 51BT, or 51CT for faults between the SEL-351A and the line recloser.
This results in the following trip setting:
TR = 51PT * SHO + 51AT + 51BT + 51CT
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 * 51P
and there is a permanent fault beyond the line recloser, the shot counter of the
SEL-351A will increment all the way to shot = 4 (see
Figure 6.9 ). If there is a
coincident fault between the SEL-351A and the line recloser, the SEL-351A
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.
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 Additional Settings
Example 2 limits sequence
coordination shot counter
incrementing.
Courtesy of NationalSwitchgear.com