SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 11 of 27
18.3 Blocking scheme
Operating conditions:
Zone 1 operation – –> instantaneous trip
Reverse Zone 3 operation without Zone 2 operation – –> transmit blocking
signal
Zone 2 operation without signal received – –> instantaneous trip
Special aspects to consider:
A delay on instantaneous tripping (t
P
) after Zone 2 operation is required to allow
time for a possible blocking signal to arrive from the relay at the other line end.
Recommended setting:
t
P
= signalling channel P/U time + x (or nearest setting above this value)
x = 25ms for quad/mho relay
= 30ms for mho/lenticular relay,
a
/
b
= 1
= 35ms for mho/lenticular relay,
a
/
b
= 0.69
= 40ms for mho/lenticular relay,
a
/
b
= 0.41
CURRENT REVERSAL AFTER NEAREST CB OPENS
In case (a) the healthy line end B relay has its Zone 2 element operated, but
instantaneous operation is blocked by carrier signal transmitted from end A. When
the relay near the fault trips, current reversal takes place in the healthy circuit and
end A ceases to transmit a blocking signal. However, it takes Zone 2 at end B a
few ms to reset. If this relay loses the blocking signal before Zone 2 has reset, an
instantaneous trip will occur on the healthy circuit. A slight delay on reset of the
signal received is therefore required to allow the relay Zone 2 elements to reset on
current reversal.
Recommended setting:
t
D
= 0 if signalling channel reset time is 10ms or greater
t
D
= 12ms if signalling channel reset time is less than 10ms
Refer to Figure 71, Chapter 2, for block diagram of blocking scheme.
A
Open
BAB
a) Fault occurs b) End A relay trips
Strong Strong
Weak
Weak
Block Block
To Next Page
Loading...