44x/EN AP/Hb6
-48 MiCOM P40 Agile
will still result in time delayed tripping. Where high speed protection is required over the
entire line, then a channel aided scheme will have to be employed.
3.2.1.2 Permissive Underreach Transfer Trip Schemes PUP Z2 and PUP Fwd
To provide fast fault clearance for all faults, both transient and permanent, along the length
of the protected circuit, it is necessary to use a signal aided tripping scheme. The simplest of
these is the permissive underreach protection scheme (PUP), of which two variants are
offered in the P442 and P444 relays. The channel for a PUP scheme is keyed by operation
of the underreaching zone 1 elements of the relay. If the remote relay has detected a forward
fault upon receipt of this signal, the relay will operate with no additional delay. Faults in the
last 20% of the protected line are therefore cleared with no intentional time delay.
Listed below are some of the main features/requirements for a permissive underreaching
scheme:
• Only a simplex signalling channel is required.
• The scheme has a high degree of security since the signalling channel is only keyed
for faults within the protected line.
• If the remote terminal of a line is open then faults in the remote 20% of the line will be
cleared via the zone 2 time delay of the local relay.
• If there is a weak or zero infeed from the remote line end, (ie. current below the relay
sensitivity), then faults in the remote 20% of the line will be cleared via the zone 2 time
delay of the local relay.
• If the signalling channel fails, Basic distance scheme tripping will be available.
P3054ENa
Figure 24: Zone 1 and 2 reaches for permissive underreach schemes
3.2.1.2.1 Permissive Underreach Protection, Accelerating Zone 2 (PUP Z2)
This scheme allows an instantaneous Z2 trip on receipt of the signal from the remote end
protection. Figure 25 shows the simplified scheme logic.
Send logic: Zone 1
Permissive trip logic: Zone 2 plus Channel Received.
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