Alstom SHPM 101, Service Manual

Page: 243 / 336

SERVICE MANUAL R5888C
QUADRAMHO Chapter 5
Page 23 of 24
In this case it can also be seen that operation would be obtained by reversing
the current and voltage rotation need not be carried out.
To enable any load condition to be understood Figure 11C provides the facility
for drawing the characteristic.
If the load vector is near the directional characteristic boundary, eg. an RCA of
85
°
and a load power factor of unity or slightly leading, then the load test may
not appear conclusive as some phases may not operate.
This may be made more conclusive by lowering the RCA temporarily by means
of ØPh.
An alternative method of making the directional check conclusive for a similar
condition is by rotating the voltage vectors through 120
°
by means of a heavy
duty test plug inserted in the 1Z position as shown in Figure 9B.
If voltage rotation is necessary it is best to select
∞
on K11 after inserting the
test plug with the rotation connections on it.
iii) A check must also be made to ensure that operation does not occur in the
reverse direction. This is achieved by inserting a test plug in the 1Y position with
links already on it, as shown in Figure 9A.
iv) After the test has been completed ensure that K11 is on its correct setting. If any
other switches have been used to assist the test ie. K1, K2 or Ø
Ph
make sure
they also are put back to their correct settings. Insert the normal 1Y and 1Z
bridging plugs.
Note: The directional characteristic may not be a perfect straight line and if a
near boundary operation occurs in the reverse direction, the normal
angular hysteresis will operate in the wrong direction until the memory has
run out. If Ø
Ph
is lowered by 10
°
the effect should disappear and no
operation be obtained.
If a self-check is done with K11 in the
∞
position without the outgoing contacts
inhibited, the relay may indicate that it is not available. When K11 is returned
to its normal position and another self-check is done on the comparators, then
relay available indications will be restored.