44x/EN AP/Hb6
-32 MiCOM P40 Agile
P3041ENa
Reverse Forward
ReverseForward
Forward
Forward
All breakers closed
Relay 3 senses reverse current
1 2
3
3
1
4
1 2
3 4
Breaker 1 opens
Relay 3 senses forward current
Forward
Weak
Source
Strong
Source
Strong
Source
Weak
Source
4
2
3
1
4
2
Figure 11: Direction reversal from sequential clearing of parallel lines
The P44x provides protection against the effects of this phenomenon by employing transient
blocking. An adjustable timer is available that will block direct and permissive transfer trip
signals from being used in the P44x logic, and will also block the P44x from sending direct or
permissive transfer trip signals. This timer is designated as “Reverse Guard Timer”.
This provides protection against fault current reversal and will still allow fast tripping in the
event of faults occurring in zone 1, if zone 1 is independent (not used as overreach zone).
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