Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 104/220 MiCOM P441/P442 & P444
3.2.3 Permissive Underreach Schemes
For a PUP scheme, the signalling channel is only keyed for internal faults. Permissive
tripping is allowed for operation of zone 2 plus receipt of a signal from either remote line end.
This makes the signalling channel requirements for a PUP scheme less demanding than for
a POP scheme. A common power line carrier (PLC) signalling channel or a triangulated
signalling arrangement can be used. This makes the use of a PUP scheme for a teed feeder
a more attractive alternative than use of a POP scheme.
The channel is keyed from operation of zone 1 tripping elements. Provided at least one
zone 1 element can see an internal fault then aided tripping will occur at the other terminals if
the overreaching zone 2 setting requirement has been met. There are however two cases
where this is not possible:
Figure 63 (i) shows the case where a short tee is connected close to another terminal. In
this case, zone 1 elements set to 80% of the shortest relative feeder length do not overlap.
This leaves a section not covered by any zone 1 element. Any fault in this section would
result in zone 2 time delayed tripping.
Figure 63 (ii) shows an example where terminal 'C' has no infeed. Faults close to this
terminal will not operate the relay at 'C' and hence the fault will be cleared by the zone 2
time-delayed elements of the relays at 'A' and 'B'.
Figure 63 (iii) illustrates a further difficulty for a PUP scheme. In this example current is
outfeed from terminal 'C' for an internal fault. The relay at 'C' will therefore see the fault as
reverse and not operate until the breaker at 'B' has opened; i.e. sequential tripping will occur.
A
Z1A
B
C
Z1C
= area where no zone 1 overlap exists
Fault
A
Z1A
B
C
Z1B
No infeed
Fault seen by A & B in zone 2
A
P3076ENa
B
C
Relay at C sees reverse fault until B opens
(i)
(ii)
(iii)
FIGURE 63 - TEED FEEDER APPLICATIONS