Areva MiCOM P441, Техническое руководство

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P44x/EN AP/E33 Application Notes
Page 38/220 MiCOM P441/P442 & P444
Data Type Description
Zp’ Internal logic Zp Decision (lock out by Power Swing)
Z4’ Internal logic Z4 Decision (lock out by Power Swing)
T1 Internal logic Elapse of distance timer 1
T2 Internal logic Elapse of distance timer 2
T3 Internal logic Elapse of distance timer 3
Tzp Internal logic Elapse of distance timer p
T4 Internal logic Elapse of distance timer 4
2.8.4.2 Outputs
Data Type Description
PDist_Dec Internal logic Trip order by Distance Protection
2.8.5 Loss of Load Accelerated Tripping (LoL)
The loss of load accelerated trip logic is shown in Figure 15. The loss of load logic 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 signalling
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.
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 recognise 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 40ms as shown in Figure 15,
although this can be altered in the menu LoL: Window cell. The accelerated trip is delayed
by 18ms 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
For circuits with load tapped off the protected line, care must be taken in setting the loss of
load feature to ensure that the I< level detector setting is above the tapped load current.
When selected, the loss of load feature operates in conjunction with the main distance
scheme that is selected. In this way it provides high speed clearance for end zone faults
when the Basic scheme is selected or, with permissive signal aided tripping schemes, it
provides high speed back-up clearance for end zone faults if the channel fails.
Note that loss of load tripping is only available where 3 pole tripping is used.