Areva MiCOM P441 - Page 167

Relay Description P44x/EN HW/E33
MiCOM P441/P442 & P444 Page 39/44
Protection against Current Reversal (Transient Blocking)
When a fault occurs on a line, which is parallel to the protected line, the pilot schemes on the
protected line may be subjected current reversals from sequential clearing on the parallel
line. A fault on the parallel line may start by appearing external to the protected line in the
reverse direction, and then, after a sequential operation of one of the parallel line breakers,
the fault appears forward. This situation can affect security of certain pilot schemes on the
protected line.
P3041ENa
Reverse Forward
ReverseForward
Forward
Forward
All breakers closed
Relay 3 senses reverse current
12
3
3
1
4
12
34
Breaker 1 opens
Relay 3 senses forward current
Forward
Weak
Source
Strong
Source
Strong
Source
Weak
Source
4
2
3
1
4
2
FIGURE 16 - 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).