TIRE & RIM AR 2049241 - Caterpillar

The high voltage that is produced by an operating generator set can cause severe injury or death. Before performing any maintenance or repairs, ensure that the generator will not start.Place the engine control switch in the "OFF" position. Attach "DO NOT OPERATE" tags to all starting controls. Disconnect the batteries or disable the starting system. Lock out all switchgear and automatic transfer switches that are associated with the generator.
Table 1
TOOLS NEEDED    
Part Number     Tool     Quantity    
142-5055     Insulation Tester
Megohmmeter     1    
Personal injury or death can result from electrocution.The megohmmeter is applying a high voltage to the circuit.To avoid electrocution, do not touch the instrument leads without first discharging them. When finished testing also discharge the generator windings.
The following materials will cause the winding insulation to deteriorate:
moisture (water)
dust
grease
other foreign matter within the generatorThis deterioration reduces the resistance of the insulation. This test will measure the resistance of the winding insulation. The insulation tester (megohmmeter) produces a high potential voltage between the test leads. During the test, a small current flows. The tester converts this current to a resistance reading.The insulation test is performed as part of periodic maintenance in order to detect the deterioration of the winding insulation. When there is a rapid decrease in the insulation resistance in a short amount of time, the generator needs to be cleaned.Note: For information on generator cleaning, refer to Special Instruction, SEHS9124.When generators have not been used for a period of time, moisture can accumulate. Therefore, the insulation test should be performed on generators that have been idle. If moisture is known to exist, the windings must be dried prior to testing. Refer to Testing And Adjusting, "Generator - Dry".The insulation test should be performed on generators that are being used for the first time. The insulation test should be performed more frequently in the following cases:
The generator set is operating in a humid environment.
The generator set is not protected from the elements in an enclosed area.
The generator set has not been run under load for three months.Note: Space heaters may need to be used around the generator set in the following cases:
The generator set has not been run under load for three months.
The generator set is exposed to a sea water environment.
The humidity is above 75 percent.
A test result was below 3 megohms.The winding needs to be reconditioned or the winding needs to be replaced in the following cases:
The measured insulation resistance falls below the specified amount. The cleanup procedure does not correct the discrepancy.
The measured insulation resistance falls below the specified amount. The drying procedure does not correct the discrepancy.The specified insulation resistance is an approximate value. It can be possible to operate the generator with less than the specified value. However, a generator that has a low winding insulation resistance will be more likely to have a failure.
Personal injury or death can result from improper troubleshooting and repair procedures.The following troubleshooting and repair procedures should only be performed by qualified personnel