Appendix L L-PRO Setting Example
D02706R02.30
L-PRO 4000 User Manual
Appendix L-23
Current
Reversal Logic
Example
The relays are installed and provide line protection by the tripping Breaker #1
and Breaker #2 respectively. A ground fault occurs at location F in the parallel
line. Initially, 21N2 of L-PRO #2 picks up and sends a permissive transfer trip
signal to L-PRO #1. Since L-PRO #1 detects a reverse fault (21N4 picks up),
it neither trips the breaker nor sends a permissive transfer trip signal. When
breaker #3 opens due to a zone 1 trip, the current reversal condition occurs on
L-PRO #1. If the 21P2 on L-PRO #1 operates, and if the received permissive
transfer trip signal from L-PRO #2 still exists the POTT scheme on L-PRO #1
will trip breaker #1. To prevent this unwanted tripping on the parallel line, the
relay has current reversal logic. The relay current reversal logic prevents the
false trip during this current reversal condition. Gate #116 of the functional
logic diagram and timer TL1 and TD1 stretch the zone 4 logic and block the
POTT scheme from tripping the breaker or sending the transfer trip signal to
the remote end.
Summary of Contents for L-PRO 4000
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