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GEI-90802
ELECTRICAL TESTS
Before the following electrical
tests are made, the relay should be in its case,
preferably mounted in its permanent location.
The relay closing angle should be set as required for its permanent location, which
would normally be 20
0 •
Connect the relay as shown in Figure 10, and check that the
relay picks up at the proper phase angle
~
3
0 .
If a phase angle meter or a phase shifter is not available, it is possible to adjust
the relay to approximately the closing angle desired
by
means of the connections and
curve shown in Figure 11.
In this test, rated voltage is held on one circuit (studs
7-8) and a reduced voltage is applied to the other circuit (studs 5-6).
The voltage
connected to studs 5-6 is adjusted until
the synchronizing-check unit just closes
its contact.
The di fference
between the two vol tages should agree approximately
with the voltage given on the curve shown in Figure 11 for the phase angle used
(e.g. 24 volts for 20
0
closing).
When
using
the
connections
shown
in either
Figure
10 or
Figure
11, check
the
operating time at 0 displacement with rated voltage on each coil, using the time-
dial setting of the permanent location.
See Figure 6 for nominal time-delay values.
Pickup and dropout of the telephone-type undervoltage relays should be checked as
described in the section on
ACCEPTANCE TESTS.
PERIODIC CHECKS AND ROUTINE MAINTENANCE
In view of the vital
role of protective relays in the operation of a power
system,
it is important that a periodic test program be followed.
The interval
between periodic checks will vary depending upon environment, type of relay and the
user's
experience with
periodic
testing.
Until
the user has accumulated enough
experience to select the test interval best suited to his individual
requirements,
it is suggested that the following points be checked once a year.
CONTACT CLEANING
A flexible burnishing tool should be used for cleaning relay contacts.
This is
a
flexible
strip
of
metal
with
an
etched-roughened
surface,
which
in
effect
resembles a superfine file.
The polishing action of this file is so delicate that
no scratches are left on the contacts, yet it cleans off any corrosion thoroughly
and rapidly.
The flexibility of the tool insures the cleaning of the actual points
of contact.
Relay contacts should not be cleaned with knives, files, or abrasive paper or
cloth.
Knives or files may leave scratches, which increase arcing and deterioration
of the contacts.
Abrasive paper
Ot'
cloth may leave minute particles of insulating
abrasive material in the contacts, and thus prevent closing.
The burnishing tool described above can be obtained from the factory.
8
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