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✓ Undervoltage elements (UVLS or UVLG) being operated.
✓ Neither forward overreaching element nor reverse looking element being operated.
Figure 2.12-9 UV for WIKT
810000EBBE DIS-WKIT BLOCK
Figure 2.12-10 WIKT logic
UV responds to three phase-to-phase voltages and three phase-to-ground voltages. UV
prevents false weak infeed tripping due to spurious operation of the channel.
WIKT can be enabled using scheme switch [Dis-WKIT] On.
2.12.6 Countermeasure for current reversal
When a fault occurs on one of the parallel lines, the reversal of fault current may be found on
another line owing to sequential CB opening. In the worst case, the current reversal can result
in false operation in POP, UOP and BOP. Thus, POP, UOP and BOP have current reversal logic
(CRL) to prevent the false operation.
Figure 2.12-11(a) shows the arrangement of parallel lines, as an example. Suppose that
a fault occurs at location F on line L1 at time t1. CB
A1
is tripped at time t2; and later, CB
B1
is tripped at time t3. The current direction on line L2 can be reversed at time t2. That is, the
current ( ) from terminal B to terminal A is found from time t1 to t2. However, the
current ( ) from terminal A to terminal B is found from time t2 to t3. The current
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