
114 SEBU8219-01
Maintenance Section
Insulation - Test
•
The generator s
et is installed in an enclosed area.
This area needs to be low in humidity and this area
needs to have steady temperatures. Test every
twelve months
(minimum).
•
The generator set has not been run under load
for three mon
ths. Test the generator set weekly.
Use space heaters around the generator set if the
generator is exposed to a sea water environment or
if the humidi
ty is above 75 percent. Also use space
heaters if a test result was below 3 megohms.
Space heater
s must be used whenever the generator
set is not under load. Space heaters must also be
used whenever salt is present or whenever high
humidity is
present. Using a space heater in this
fashion is the only way to maintain insulation tester
readings above one megohm. Use space heaters
only when th
e generator is not running.
For additional information, refer to Special Instruction,
SEHS9124,
“Cleaning and Drying of Electric Set
Generators”.
Recommended Periodic Insulation
Test Proce
dure
Personal injury or death can result from electro-
cution.
The megohmmeter is applying a high voltage to
the circu
it.
To avoid electrocution, do not touch the instru-
ment lead
s without first discharging them. When
finished testing also discharge the generator
windings.
1. Take the generator out of service.
2. Visually
inspect the generator for moisture. If
moisture exists, do not perform this insulation
test. Dry the u nit first. Refer to Special Instruction,
SEHS912
4, “Cleaning and Drying of Electric Set
Generators”.
3. Inspect
the installation. Determine the equipment
that will be tested by the insulation tester.
4. Disch ar
ge the capacitance of the windings.
5. Disconnect “T0” from ground.
6. Disconnect the regulator sensing lead wires: “20”,
“22”, and “24”.
7. Connect the insulation tester’s RED lead to
ground.
8. Connect the ins
ulation tester’s BLACK lead to
“T0”.
9. For units that
are 600 volts or less, set the voltage
to 500 Volts. For units that are more than 600
volts, set the voltage to 1000 Volts.
10. Use the 30/60 Time Resistance Method:
a. Apply voltage
.
b. Observe the readings at 30 seconds. Observe
the readings
at 60 seconds.
c. Record the 60 second reading. This reading
must be corre
cted for temperature.
d. Record temperature.
e. Record humidity.
f. Remove volta
ge.
11. Evaluate the readings. The actual value of the
resistance m
ay vary greatly between generators.
For this reason, the insulation’s condition must be
evaluated. Base this evaluation on the comparison
between the
60 second resistance readings and
the readings that were taken on previous dates.
These two readings must be taken under similar
conditions
. If a 60 second resistance reading
has a 50 percent reduction from the previous
reading, the insulation may have absorbed too
much moist
ure.
Switch the insulation teste r to the “OFF” position.
This will d
ischarge the insulation tester’s leads.
Disconnect the insulation tester’s leads.
Note: The r
esults from the insulation resistance
checks indicate when cleaning and/or repairing is
becoming critical. Generally, insulation resistance
will vary
greatly with temperature. Therefore, always
test at the same temperature and humidity. Refer to
Illustration 81.
Engine Serial Number
_____________________________________
Generato
r Serial Number
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