Alstom MiCOM P54 Series, Technical Manual

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Operation P54x/EN OP/La4
MiCOM P543, P544, P545 & P546
(OP) 5-75
OP
1.24.1 Zone 1 extension scheme (Distance option only)
Auto-reclosure is widely used on radial overhead line circuits to re-establish supply following
a transient fault. A Zone 1 extension scheme may therefore be applied to a radial overhead
feeder to provide high speed protection for transient faults along the whole of the protected
line. Figure 50 shows the alternative reach selections for zone 1: Z1 or the extended reach
Z1X.
P1308ENa
B
A
ZL
Z1 Extensi o n (B)
Z1 Extensi o n (A)
Z1 A
Figure 50 Zone 1 extension scheme
In this scheme, Zone 1X is enabled and set to overreach the protected line. A fault on the
line, including one in the end 20% not covered by zone 1, will now result in instantaneous
tripping followed by auto-reclosure. Zone 1X has resistive reaches and residual
compensation similar to Zone 1. The auto-recloser in the relay is used to inhibit tripping from
zone 1X such that upon reclosure the relay will operate with Basic scheme logic only, to co-
ordinate with downstream protection for permanent faults. Therefore, transient faults on the
line will be cleared instantaneously, which will reduce the probability of a transient fault
becoming permanent. The scheme can, however, operate for some faults on an adjacent
line, although this will be followed by auto-reclosure with correct protection discrimination.
Increased circuit breaker operations would occur, together with transient loss of supply to a
substation.
The time delays associated with extended zone Z1X are shown in the table below:
Scenario Z1X time delay
First fault trip = tZ1
Fault trip for persistent fault on auto-reclose = tZ2
The Zone 1X reach is set as a percentage of the Zone 1 reach, i.e. as a reach multiplier.
The Zone 1 extension scheme can be
Disabled
, permanently
Enabled
or just brought into
service when the distance communication channel fails and the aided scheme would be
inoperative. A selection of which out of the two channels available in the MiCOM P54x is
monitored, is provided, with selections from Channel 1 and Channel 2 in any combination.
The Logic Diagram is shown in Figure 51 below: