SERVICE MANUAL R5888C
QUADRAMHO Chapter 5
Page 16 of 24
to the right, check that the signal send contacts will close when the reset button is
pressed.
Note: other contacts may also operate, depending on the position of the other
SW switches.
5.2.4 Signal receive check
There is another test option which enables the checking of the signal receive.
If test option 41 is selected, the LED labelled SOTF will illuminate when the opto
isolator input is energised.
5.2.5 Block auto reclose checks
Switch SW6 controls whether or not auto reclose is blocked when the channel is
out of service.
If SW6 is set to the right, check that the block auto reclose contact (Terminals
B25–26) is closed.
Energise the channel in service input (A7–8) and check that the block auto reclose
contact opens.
If SW6 is set to the left, check that the block auto reclose contact does not close if
the channel in service signal is present.
5.3 Blocking scheme (06 or 07)
Note that if the channel in service opto isolator is not energised, 3 phase trips will
be given in scheme 06.
In this scheme a block signal is sent when a particular Zone 3 comparator
operates and the corresponding Zone 2 comparator does not.
The Zone 3 will generally have a larger reverse reach than forward reach.
(The smallest forward phase fault reach is Z
Ph
and if PSB is used greater than
Zone 2). An aided trip occurs when a Zone 2 comparator operates, the channel in
service opto isolator is energised and no block signal is received, certain time
delays are necessary to prevent maloperations. These time delays have to be set to
take into account different signalling channel times, comparator operation times
and logic processing times.
t
p
is the set time delay tripping after the Zone 2 comparator has operated to allow
a possible blocking signal to be received from the relay at the other line end.
The recommended setting is:
t
p
= channel pick up time + 25ms for Quadramho with mho
30ms for lenticular with a/b = 1
35ms for lenticular with a/b = 0.67
40ms for lenticular with a/b = 0.41
or the nearest available higher setting.
For current reversal conditions, a small delay on drop-off of the blocking signal is
required to prevent unwanted trips while the Zone 2 comparator is resetting.
The inherent relay processing time, the reset time of the send contact and the
channel reset time mean that only an exceptionally fast channel reset time makes a
setting of anything other than t
D
= 0 necessary.
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