Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 44/220 MiCOM P441/P442 & P444
2.9.2 Permissive Overreach Transfer Trip Schemes POP Z2 and POP Z1
The P441, P442 and P444 relays offer two variants of permissive overreach protection
schemes (POP), having the following common features/requirements:
•
The scheme requires a duplex signalling channel to prevent possible relay
maloperation due to spurious keying of the signalling equipment. This is necessary
due to the fact that the signalling channel is keyed for faults external to the protected
line.
•
The POP Z2 scheme may be more advantageous than permissive underreach
schemes for the protection of short transmission lines, since the resistive coverage of
the Zone 2 elements may be greater than that of the Zone 1 elements.
•
Current reversal guard logic is used to prevent healthy line protection maloperation for
the high speed current reversals experienced in double circuit lines, caused by
sequential opening of circuit breakers.
•
If the signalling channel fails, Basic distance scheme tripping will be available.
2.9.2.1 Permissive Overreach Protection with Overreaching Zone 2 (POP Z2)
This scheme is similar to that used in the AREVA LFZP and LFZR relays. Figure 20 shows
the zone reaches, and Figure 21 the simplified scheme logic. The signalling channel is
keyed from operation of the overreaching zone 2 elements of the relay. If the remote relay
has picked up in zone 2, then it will operate with no additional delay upon receipt of this
signal. The POP Z2 scheme also uses the reverse looking zone 4 of the relay as a reverse
fault detector. This is used in the current reversal logic and in the optional weak infeed echo
feature.
Send logic: Zone 2
Permissive trip logic: Zone 2 plus Channel Received.
P3054XXa
ZL
Z1A
A B
Z1B
Z2A
Z2B
FIGURE 20 - MAIN PROTECTION IN THE POP Z2 SCHEME