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 TM 55-1905-223-24-3
NOTE
A reading of less than 1.2 megohms indicates that the permanent magnet
exciter insulation is marginal or that there is an accidental grounding.
(25)
Remove the permanent magnet exciter stator. Check the exciter and the leads going to the plug for
worn or damaged insulation.
(26)
Repair any damaged lead insulation with vinyl tape.
(27)
Dry the permanent magnet exciter stator and test again. Refer to step i. of this procedure.
i. Drying generator windings.
(1)
For generators connected to a runable engine, remove the terminal box sides. Connect the three
generator output leads together and connectthis junction to the frame ground. This is a grounded
three-phase short circuit connection.
NOTE
Wires connecting the generator output leads together must be capable of carrying 3/4 of the rated
generator output amps. The wire connecting the junction of the three output leads to the frame must
be #10 or larger.
(2)
Remove the AVR from the AVR box by removing the four cover captive screws, the cover, the four
threaded pillars, and then the AVR. Remove the X and XX leads from the AVR.
NOTE
Use a dc power source or storage battery, capable of producing 0.5 amp at 12 volts but not exceeding
13.2 volts to provide power to the generator X and XX leads.
(3)
Connect the positive (+) lead of power supply to the main exciter lead X at the AVR. Connect the
negative (-) power supply lead to the dc exciter lead XX.
(4)
Start the engine. After 5 minutes at low idle, bring the engine up to rated speed.
(5)
After 1 hour at rated speed, stop the engine, disconnect the voltage form the dc exciter, and isconnect
d
the shorted generator output leads from the generator frame.
(6)
Measure the main stator insulation resistance with the megger. Refer to step h. procedures.
(7)
The generator is satisfactory if the reading is 1.5 megohms or above.
(8)
If the readings are below 1.5 megohms, continue drying.
4-15
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