Generac Power Systems 940-2 Test All Stator Windings To Ground, Test For Shorts Between Windings

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 +1
RESISTANCE
(in “megohms”)	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.

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.

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.).

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