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Section 3
INSULATION RESISTANCE TESTS
vents that will not attack such materials.
Use a soft brush or cloth to apply the solvent. Be
careful to avoid damage to wire or winding insulation.
After cleaning, dry all components thoroughly using
moisture-free, low-pressure compressed air.
*
DANGER!: DO NOT ATTEMPT TO WORK
WITH SOLVENTS IN ANY ENCLOSED AREA.
PROVIDE ADEQUATE VENTILATION WHEN
WORKING WITH SOLVENTS. WITHOUT
ADEQUATE VENTILATION, FIRE, EXPLOSION
OR HEALTH HAZARDS MAY EXIST . WEAR
EYE PROTECTION. WEAR RUBBER GLOVES
TO PROTECT THE HANDS.
CLOTH OR COMPRESSED AIR:
For small parts or when dry dirt is to be removed, a
dry cloth may be sufficient. Wipe the parts clean, then
use low pressure air at 30 psi (206 Kpa) to blow dust
away.
BRUSHING AND VACUUM CLEANING:
Brushing with a soft bristle brush followed by vacuum
cleaning is a good method of removing dust and dirt.
Use the soft brush to loosen the dirt, then remove it
with the vacuum.
STATOR INSULATION RESISTANCE
GENERAL:
Insulation resistance is a measure of the integrity of
the insulating materials that separate electrical wind-
ings from the generator’s steel core. This resistance
can degrade over time due to the presence of con-
taminants, dust, dirt, grease and especially moisture.
The normal insulation resistance for generator wind-
ings is on the order of “millions of ohms” or “mego-
hms”.
When checking the insulation resistance, follow the
tester manufacturer’s Instructions carefully. Do NOT
exceed the applied voltages recommended in this
manual. Do NOT apply the voltage longer than one
(1) second.
*
CAUTION!: DO NOT connect the Hi-Pot Tester
or Megohmmeter test leads to any leads that
are routed into the generator control panel.
Connect the tester leads to the Stator or Rotor
leads only.
STATOR SHORT-TO-GROUND TESTS:
See Figure 3-2. To test the Stator for a short-to-ground
condition, proceed as follows:
1. Disconnect and Isolate all Stator leads as follows:
a. Disconnect sensing leads 11S and 22S from
the voltage regulator.
b. Disconnect excitation winding lead No. 6 from
the voltage regulator.
c. Disconnect excitation lead No. 2 from the volt-
age regulator (VR).
e. At the main circuit breakers, disconnect AC
power leads No. 11 and 33.
f. At the 4-tab ground terminal (GRD2), discon-
nect Stator power leads No. 22 and 44.
2. When all leads have been disconnected as out-
lined in Step 1 above, test for a short-to-ground
condition as follows:
a. Connect the terminal ends of all Stator leads
together (11S, 22S, 11, 22, 33, 44, 2, & 6).
b. Follow the tester manufacturer’s instructions
carefully. Connect the tester leads across
all Stator leads and to frame ground on the
Stator can. Apply a voltage of 1500 volts. Do
NOT apply voltage longer than one (1) sec-
ond.
If the test indicates a breakdown in insulation, the
Stator should be cleaned, dried and re-tested. If the
winding fails the second test (after cleaning and dry-
ing), replace the Stator assembly.
TEST BETWEEN ISOLATED WINDINGS:
1. Follow the tester manufacturer’s instructions care-
fully. Connect the tester test leads across Stator
leads No. 11 and 2. Apply a voltage of 1500 volts-
DO NOT EXCEED 1 SECOND.
2. Repeat Step 1 with the tester leads connected
across the following Stator leads:
a. Across Wires No. 33 and 2.
b. Across Wires No. 11 and 33.
c. Across Wires No. 11 and 2.
If a breakdown in the insulation between isolated
windings is indicated, clean and dry the Stator. Then,
repeat the test. If the Stator fails the second test,
replace the Stator assembly.
TEST BETWEEN PARALLEL WINDINGS:
Connect the tester leads across Stator leads No. 11
and 33. Apply a voltage of 1500 volts. If an insula-
tion breakdown is indicated, clean and dry the Stator.
Then, repeat the test between parallel windings. If the
Stator fails the second test, replace it.
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