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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
sary to disassemble the relay. It is very important to
line protection, or backup protection when more
follow the manufacturer's printed procedures. Re-
complex relays are used for primary protection to
placement parts are available, but their use is not
provide additional reliability.
recommended. Printed circuit boards are easily
(1) Nondirectional units. Nondirectional
damaged. Direct replacement does not necessarily
overcurrent relays should be tested at several
mean the relay will operate properly, without fur-
points on the timecurrent curve, allowing suitable
ther calibration or verification. When more than
intervals between tests for cooling. Measure the re-
inspection and operating checks are necessary, it is
set time and minimum operating current. Check
recommended that the relay be returned to the
instantaneous element for pickup and contact ac-
manufacturer.
tion at high and low currents. Caution should be
11-6. Relay performance tests.
exercised so as not to "burn up" the relay when
testing on high currents, or continuously testing at
These tests are usually provided for equipment ac-
lower currents. Test connections for overcurrent re-
ceptance, but may be necessary if the relay is com-
lays are shown in figure 11-l.
pletely replaced.
(2) Directional overcurrent relay. Check the
a. Operational checks. Before returning a relay to
overcurrent element in the same manner as for a
service, test the complete wiring installation for
nondirectional overcurrent relay. Before testing the
continuity and operate the relay contacts, prefer-
overcurrent element, verify the operation of the di-
ably by test current, to ensure that everything is in
rectional element by simulated fault currents and
order for the intended function. Any changes in the
voltages. Check the minimum operating current of
relay calibration, or needed adjustments should be
the overcurrent element at normal voltage, and
made at this time. Normally adjustments in the
check the contact gap spacing of the directional ele-
relay settings will not be necessary, but proof checks
ment. For typical test connections, see figure 11-2.
must be made. Manufacturers' instruction books
should also be checked to determine the proper pro-
b. Differential relays. Figure 11-3 shows a typical
cedure and test equipment required for specific re-
test connection for a percentage differential type.
lays. In some cases, the relay may have to be re-
Check the minimum operating values at zero re-
moved and inspected in a laboratory.
straining current and the operating points at sev-
b. Directional test. Where directional relays are
eral values of restraint. The slope (differential char-
acteristic) and, where applicable, the harmonic
used, an overall test should be made to ensure that
restraint feature should also be checked. It may be
they operate in the proper direction.
desirable to trip all circuit breakers from differen-
c. Dielectric test. When dielectric or insulation
tial relays as a regular testing procedure.
tests are made, they should be performed on the
complete installation or on all the component parts.
For relays rated up to 6000 volts, the test should be
angles, angle of maximum torque, and directional
made at twice rated voltage plus 1000 volts (with a
characteristics. Test operating sequences, including
minimum of 1500 volts ac for one minute).
time, contact resistances, and relay reach, at vari-
d. Calibration and performance tests. Some of the
ous load power factors and settings. Figure 11-4
tests that are run on the more common relays are
shown herein. In addition, the manufacturer's in-
struction book should be checked for proper testing
procedure of a specific relay. The time between tests
will be determined by installation conditions and
changes in the system. Regularly scheduled tests
should be supplemented by special tests, made at
any time protective equipment damage is suspected
and while protected equipment is out of service.
11-7. Common electromechanical relay tests.
Always follow the manufacturer's instruction
manual for tests and checks. The following informa-
tion provides generalized test connections for the
most common type relays used on military installa-
tions. Actual test connections may be more complex.
a. Overcurrent relays. Overcurrent relays are the
Figure 11-l. Typical test connection for a nondirectional
relays most often used. They provide either primary
overcurrent relay
11-3
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