SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 10 of 27
A has ceased to transmit a signal. It may be that end B will cease to receive a
signal before its Zone 2 element picks up, in which case there would not be a fast
trip. It is therefore necessary to have a delay on reset of the signal received, so
that in the case above, end B will be allowed to fast trip when its Zone 2 element
picks up.
Time delay t = 100ms
Refer to Figure 68, Chapter 2 for block diagram of permissive underreach scheme.
18.2 Permissive overreach scheme
Operating conditions:
Zone 1 operation – –> instantaneous trip
Zone 2 operation – –> signal send
Zone 2 operation + signal receive – –> instantaneous trip
CURRENT REVERSAL AFTER NEAREST CB OPENS
The current reversal guard incorporated in the scheme logic is initiated when a
healthy circuit relay receives a permissive trip signal, but does not have a Zone 2
element picked up. A delay on pick up (tp) of the current reversal guard is
necessary in order to allow time for Zone 2 elements to pick up, if they are going
to time, for an internal fault.
Recommended setting tp = 30ms – signalling channel P/U time
(or nearest setting above this value)
Once the current reversal guard has picked up (healthy circuit relay at end A),
transfer tripping is inhibited. The reset of the guard is initiated by either the loss of
permissive trip signal or by the pick up of a Zone 2 element. A time delay (t
D
) for
the reset of the reversal guard, is required in case the Zone 2 element (end A)
picks up before the permissive trip signal from the other relay (end B) has reset
which could cause healthy circuit tripping.
Recommended setting t
D
= signalling channel D/O time + 25ms
(or nearest setting above this value)
Refer to Figures 69 and 70, Chapter 2, for block diagram of permissive overreach
scheme.
A
Open
BAB
a) Fault occurs b) End A relay trips
Strong Strong
Weak Weak
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