GEK-49861
(g) As the voltage is lowered, observe the waveform at the test
point
designated
in step e) .
At the
point where the
telephone r elay (K2) picks up, a slight adjustment of the
phase angle and input voltage will cause the waveform to be
reduced
to
a
null
consisting
of
only
third
and
fifth
harmonics.
At this null point, the angle on the phase angle
meter is the base reach angle
0
and should be within 2° of
the nominal value of 85°.
The voltage VT at this null
condition should be within 5% of the value calculated by
equation {1) .
NOTE:
The measured pickup should agree with the calculated
value within ±5%.
If the values do not agree within
these limits, it is recommended that the test setup and
meter calibrations be checked before the factory settings
on the relay are disturbed.
One good method of checking
the test set up and procedure is to repeat the tests on a
duplicate relay.
{h) If it is desired to readjust the reach so that measured
pickup occurs at a value closer to the calculated value, this
may be accomplished by means of the trim potentiometers on
the SP card.
The potentiometer to be adjusted for each phase
is shown in Table XIV.
These potentiometers should be turned
clockwise to incr ease the reach.
TABLE XIV
REACH ADJUSTMENT LOCATIONS
PHASE UNDER TEST
POTENTIOMETER
DESIGNATION
AB
BC
CA
Pl
P3
P5
{ i) Replace the "OSB" plug in the "IN" position if blocking of
main
output
contacts
is
desired
during
an
out-of-step
condition (Type SLY81B only) .
3.
Mho Characteristics
The complete mho characteristic can be measured by the test
circuit shown in Figure 31.
The test circuit shown in Figure
24 may also be used for measuring the complete mho characteristic,
but, if this circuit is used, the test results may indicate that the
characteristic pulls back at some angles.
This pull back is due to
an inadequate amount of positive-sequence polarizing voltage being
produced by this circuit.)
The procedure is similar except that the
phase shifter is adjusted until the phase angle meter indicates the
angle of interest.
Reduce the voltage out of the variac until the
relay picks up and the value of VT at this point should be as given
by equation {3) .
21
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