C1.5 and C2.2 Generator Caterpillar

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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 generator

This 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 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.

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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 familiar with this equipment.

The insulation test gives accurate results only when the generator windings are free of moisture and the generator windings are at room temperature.

Each winding must have a minimum insulation resistance of one megohm.

Main Armature (Stator L4)

1. Remove the load from the generator by either of the following:
   • open the line circuit breaker

   • open the load connections to (T1), (T2), (T3), and (T0)

   Prevent these wires from coming into contact with each other and prevent these wires from contacting ground.

2. Isolate main armature (L4) from the voltage regulator by disconnecting the voltage sensing wires. If generator lead (T0) is connected to the generator frame or ground, open the connection.

3. Connect one test lead of the insulation tester (megohmmeter) to the generator enclosure (ground).

4. Connect the other test lead of the insulation tester (megohmmeter) to generator lead (T0) .

5. The insulation resistance must be one megohm or more.

Exciter Field (Stator L1)

1. Isolate exciter field (L1) from the voltage regulator by disconnecting wires 5+ and 6-. Prevent these wires from coming into contact with each other and prevent these wires from contacting ground.

2. Connect one test lead of the insulation tester (megohmmeter) to the generator enclosure (ground).

3. Connect one test lead of the insulation tester (megohmmeter) to exciter field lead (5+ or 6-).

4. Measure the resistance of the exciter field winding insulation to ground. The insulation resistance must be a minimum of 0.25 megohm (250000 ohms).

Exciter Armature (Rotor L2)

1. Isolate exciter armature (L2) from the rectifier circuit. Disconnect the three wires of the exciter armature from the rectifier blocks.

2. Connect one test lead of the insulation tester (megohmmeter) to the rotor shaft.

3. Connect one test lead of the insulation tester (megohmmeter) to any one exciter field lead.

4. The insulation resistance must be a minimum of 0.25 megohm (250000 ohms).