Alstom MiCOM P546 - 1.24.2 Loss of load accelerated tripping (LoL) (Distance option only)

P54x/EN OP/La4 Operation
(OP) 5-76 MiCOM P543, P544, P545 & P546
OP
DDB Zone 1 Extension Active (876)
&
P1548ENb
DDB Reset Z1 Extension (490)
SET Z1X Enabled
SET Z1X on Ch 1 Fail
DDB Channel 1 Fail (317)
DDB Channel 2 Fail (318)
SET Z1X on Ch 2 Fail
SET Z1X on Ch 1 AND 2 Fail
SET Z1X on Ch 1 OR 2 Fail
&
1
&
&
1
&
Figure 51 Zone 1 extension
1.24.2 Loss of load accelerated tripping (LoL
) (Distance option only)
The loss of load accelerated trip logic is shown in abbreviated form in Figure 52. The loss of
load logi
c provides fast fault clearance for faults over the whole of a double end fed
protected circuit for all types of fault, except three phase. The scheme has the advantage of
not requiring a signaling channel. Alternatively, the logic can be chosen to be enabled when
the channel associated with an aided scheme has failed. This failure is detected by
permissive scheme unblocking logic, or a Channel Out of Service (COS) opto input. 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.
Any fault located within the reach of Zone 1 will result in fast tripping of the local circuit
breaker. For an end zone fault with remote infeed, the remote breaker will be tripped in
Zone 1 by the remote relay and the local relay can recognize this by detecting the loss of
load current in the healthy phases. This, coupled with operation of a Zone 2 comparator
causes tripping of the local circuit breaker.
Before an accelerated trip can occur, load current must have been detected prior to the fault.
The loss of load current opens a window during which time a trip will occur if a Zone 2
comparator operates. A typical setting for this window is 40 ms as shown in Figure 52,
althoug
h this can be altered in the menu LoL Window cell. The accelerated trip is delayed
by 18 ms to prevent initiation of a loss of load trip due to circuit breaker pole discrepancy
occurring for clearance of an external fault. The local fault clearance time can be deduced
as follows:
t = Z1d + 2CB + LDr + 18ms
Where:
Z1d = Maximum downstream zone 1 trip time
CB = Breaker operating time
LDr = Upstream level detector (LoL: I<) reset time