SUPPORT AS 5568999 - Caterpillar

Recommended Periodic Insulation Tests
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.
Note: The results from the insulation resistance checks indicate when cleaning and/or repairing is becoming critical. Generally, insulation resistance will vary greatly with temperature. Therefore, always test at the same temperature and humidity. Refer to Illustration 1.
Illustration 1 g00633226Periodically, use an insulation tester to check the insulation resistance of the generator's main stator winding. Caterpillar recommends the 142-5055 Insulation Testing Gp for testing the insulation resistance on Caterpillar generator sets. The frequency of this test is determined by the generator's environment. Previous insulation tester readings will also determine the frequency of this test.Test the main stator windings with an insulation tester in the following situations:
The generator set is started for the first time.
The generator set is removed from storage.
The generator set is operating in a humid environment. Test every three months.
The generator set is not protected from the elements in an enclosed area. Test every three months.
The generator set is installed in an enclosed area. This area needs to be low in humidity and this area needs to have steady temperatures. Test every twelve months (minimum).
The generator set has not been run under load for three months. Test the generator set weekly.For additional information, refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".Recommended Periodic Insulation Test Procedure
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.
Take the generator out of service.
Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first. Refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".
Inspect the installation. Determine the equipment that will be tested by the insulation tester.
Discharge the capacitance of the windings.
Disconnect "T0" from ground.
Disconnect the regulator sensing lead wires: "20", "22" and "24".
Connect the insulation tester's RED lead to ground.
Connect the insulation tester's BLACK lead to "T0".
For units that are 600 volts or less, set the voltage to 500 Volts. For units that are more than 600 volts, set the voltage to 1000 Volts.
Use the 30/60 Time Resistance Method:
Apply voltage.
Observe the readings at 30 seconds. Observe the readings at 60 seconds.
Record the 60 second reading. This reading must be corrected for temperature.
Record temperature.
Record humidity.
Remove voltage.
Evaluate the readings. The actual value of the resistance may vary greatly between generators. For this reason, the insulation's condition must be evaluated. Base this evaluation on the comparison between the 60 second resistance readings and the readings that were taken on previous dates.