Generac Power Systems 941-2 Service Manual page 20

Section 1.4
INSULATION RESISTANCE
TEST ALL STATOR WINDINGS TO GROUND
Connect the ends of all Stator leads together. Make
sure none of the leads are touching any terminal or
any part of the generator.
Connect one Tester probe to the junction of all Stator
leads; the other Tester probe to a clean frame ground
on the Stator. Apply a voltage of 1000 volts for about
1 second.
Follow the tester manufacturer's instructions carefully.
Some "Hi-Pot" testers are equipped with a
"Breakdown" light which will turn ON to indicate an
insulation breakdown.
A "Megger" (Megohmmeter) will indicate the
"megohms" of resistance. Normal Stator winding
insulation resistance is on the order of "millions of
ohms" or "megohms". The MINIMUM acceptable
insulation resistance reading for Stators can be calcu-
lated using the following formula.
MINIMUM INSULATION
= GENERATOR RATED VOLTS
RESISTANCE
(in "megohms")
EXAMPLE: Generator rated voltage Is "120 VAC".
Divide 120 by 1000 to obtain "0.12". Add "1" to
obtain "1.12". Minimum Insulation resistance for
the unit Is "1.12 megohms".
TEST FOR SHORTS BETWEEN WINDINGS
Figure 2 on the previous page shows the Stator leads
that are brought out of the Stator. Figure 3 is a
schematic representation of the eight (8) Stator wind-
ings. To test for shorts between windings, proceed as
follows:
1. Make sure all Stator output leads are isolated from each other
and from the frame.
2. POWER PHASE TO TIMING WINDINGS:- Connect one tester
probe to Stator lead AC1, the other test probe to Stator lead
TIM1. Apply a voltage of 1000 volts. The Tester will indicate a
breakdown if the windings are shorted together. Repeat again
with stator lead SL1.
3. POWER PHASE TO POWER SUPPLY WINDINGS: Connect
one tester probe to Stator lead AC1, the other tester probe to
Stator lead PS1. Apply 1000 volts. If a breakdown Is indicated,
the windings are shorted together. Repeat again with stator lead
SL1.
Page 1.4-2
+1
1000
4. POWER PHASE TO BATTERY CHARGE WINDINGS:Connect
one tester probe to Stator Lead AC1, the other probe to Stator
lead No. 55. Apply 1000 volts. If breakdown Is indicated, the
windings are shorted together. Repeat again with stator lead
SL1.
5. TIMING TO POWER SUPPLY WINDING:- Connect one tester
probe to Stator lead No. TM1, the other test probe to Stator
lead No. PS1. Apply 1000 volts. If breakdown is indicated, the
windings are shorted together.
6. TIMING TO BATTERY CHARGE WINDING:- Connect one test
probe to Stator lead No. TIM1, the other test probe to Stator
lead No. 55. Apply 1000 volts. If breakdown is indicated the
windings are shorted together.
7. POWER SUPPLY TO BATTERY CHARGE WINDING:Connect
one test probe to Stator lead No. PS1, the other probe to Stator
lead No. 55. Apply 1000 volts. If breakdown is indicated, the
windings are shorted together.
RESULTS OF TESTS
1. If testing indicates that Stator windings are shorted to ground,
the Stator should be cleaned and dried. The insulation resis-
tance tests should then be repeated. If, after cleaning and dry-
ing, the Stator again fails the test, replace the Stator assembly.
2. If testing indicates that a short between windings exists,
clean and dry the Stator. Then, repeat the tests. If Stator
fails a second test (after cleaning and drying), replace the
Stator assembly.
CLEANING THE GENERATOR
GENERAL:
If testing indicates that the insulation resistance is
below a safe value, the winding should be cleaned.
Proper cleaning can be accomplished only while the
generator is disassembled. The cleaning method
used should be determined by the type of dirt to be
removed. Be sure to dry the unit after it has been
cleaned. An electric motor repair shop may be able to
assist with cleaning. Such shops are often experi-
enced in special problems (sea coast, marine, wet-
land applications, etc.).