TM 5-685/NAVFAC MO-912
(j) Note that differential relays are usually
two exceeds the setting of the relay. The relay
very sensitive devices that use polarized sensing
senses the difference between the current of one
circuitry. Repeat the pickup test. Use the second
generator and the current of another generator or
test for comparison with previous and future test
the average of all other generators. Relay output
data. Refer to manufacturer's instructions.
may be used to trip bus tie contactors and split a
c. Record keeping. Equipment and system log
parallel system to remove an unbalance.
sheets are important and necessary functions of
(h) Ground fault protection. Ground fault
record keeping. The log sheets must be specifically
protection is usually provided by a ground sensor
developed to suit auxiliary use.
d. Troubleshooting. Perform troubleshooting pro-
lines to the load in a three-phase system. Another
relay is sometimes added to the transformer
cedures when abnormal operation of the system or
neutral-to-ground connection for backup.
equipment is observed. Maintenance personnel
must then refer to records for interpretation and
b. Testing of relays. Periodic testing of relays is
comparison of performance data, i.e., log sheets.
considered preventive maintenance. The preventive
Comparisons of operation should be made under
maintenance program is built around records and
equal or closely similar conditions of load and ambi-
visual inspections and includes analysis of the
ent temperature. The general scheme for trouble-
shooting is outlined in the following table.
(1) The frequency of testing is dependent on
the variables involved i.e., type of relay, environ-
Table 5-3. Relay troubleshooting.
mental conditions, history, and experience. The am-
bient operating temperature must be recorded.
Most relays have draw-out construction so that a
relay can be separated from its enclosure. Discon-
Refer to manufacturer's l i t e r a t u r e for specific information on
nection for test or repair is usually not required.
(2) Checks and tests to be performed are deter-
mined by the type of relay. The schedule for perfor-
MAGNET-OPERATED INSTANTANEOUS TYPE
mance of tests should comply with the requirements
High Trip Action
of AR 420-43. Proceed as follows:
Install coil with correct rating
(a) Inspect the relay cover before testing. Re-
Low Trip Action
move dust and other foreign matter to prevent it
Shorted turns on high trip
Test coil and replace with new coil
from entering the relay. Record the inspection re-
if found defective
Mechanical binding; dirt, corrosion Clean parts
(b) Check relay for "flag" indication. Also,
check cover glass for fogging. If fogging is excessive,
See manufacturer's instructions
investigate the cause.
MAGNET-OPERATED INVERSE-TIME TYPE
(c) Check all connections for proper tight-
Slow Action Trip
ness. If necessary, tighten to proper torque value.
Fluid too heavy, vent too small, or Change fluid and open vent
(d) Check a rmature and connect gaps. Com-
temperature too low
slightly, regulate temperature
pare with previous measurements. Adjust gaps if
Replace and adjust
necessary and refer to manufacturer's instructions.
Fast Trip Action
(e) Check contacts for burned or eroded con-
Worn, broken parts
Replace and adjust
dition. Burnish if necessary and refer to manufac-
Fluid too light, vent too large or
Change fluid to proper grade Close
temperature too high
vent slightly or regulate tempera-
(f) Verify proper contact operation. Open or
ture. Clean dashpots and refill with
close contacts to observe proper trip or reclose ac-
fresh fluid or proper grade
tion and refer to manufacturer's instructions.
(g) Apply current or voltage to verify that
Fails to Trip Causing Motor Burnout
pickup is within manufacturer's tolerances.
Wrong size heater
Check rating with recommenda-
(h) Reduce th e current until the relay drops
tions on instruction sheet
out or fully resets. Verify that there is no binding
Mechanical binding; dirt, corrosion Clean and adjust
during operation and refer to manufacturer's in-
Relay damaged by short circuit
(i) Verify that related devices such as capaci-
Motor and relay in different ambi-
install motor and control near each
tors are functioning properly and refer to manufac-
other or make temperature uniform