SR4 HV and SR4B HV Generators Caterpillar

• Help in finding faults or help in finding weaknesses.

• Give some indication of the service reliability that can be expected.

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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.

Refer to Safety Section, "Generator Isolating for Maintenance" for information regarding the procedure to safely isolate the generator.

Recommended Periodic Insulation Tests

Periodically, use a megohmmeter to check the insulation resistance of the generator's main stator winding. The frequency of this test is determined by the generator's environment. Previous megohmmeter readings will also determine the frequency of this test.

Test the main stator windings with a megohmmeter 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 six months.

• The generator set has not been run under load for three months. Test the generator set weekly. Use space heaters around the generator set if the generator is exposed to a sea water environment or if the humidity is above 75%. Also use space heaters if a test result was below 3 megohms.

Space heaters must be used whenever the generator set is not under load. Space heaters must also be used whenever salt is present or whenever high humidity is present. Using a space heater in this fashion is the only way to maintain megohmmeter readings above one megohm. Use space heaters only when the generator is not running.

Insulation Resistance Tests at Low Voltage

Insulation resistance checks at low voltage are usually made on an armature or these tests are made on portions of an armature. These tests indicate the degree of contamination that is present on the surface of the insulation. Testing insulation resistance at low voltage also reveals contaminated solid insulation. Moisture can contaminate solid insulation and other influences can contaminate solid insulation. These tests will not usually reveal complete ruptures and these tests will not usually reveal uncontaminated ruptures.

Insulation resistance tests are based on determining the current that goes through the insulation and the current that goes across the surface of the insulation. This current is measured when a direct voltage is applied. The amount of current is dependent on the following factors:

• The amount of voltage

• The time of application

• The area of the insulation

• The thickness of the insulation

• Temperature conditions during the test

• Humidity during the test

The insulation resistance test is used in order to determine the condition of the insulation. These tests should be performed prior to more extensive testing.

Contact a Caterpillar dealer or refer to "I.E.E.E. Standard 432-1992" when more extensive tests are required.

Exciter Field (Stator)

1. Disconnect the exciter leads from the terminals that are located in the terminal box.

2. Connect the exciter leads to one clamp of a 500 volt megohmmeter. Connect the second megohmmeter's lead to the generator frame.

3. Apply 500 volts from the megohmmeter. Measure the resistance reading after one minute. The minimum reading should be 1.0 megohm. If the reading is less than 1.0 megohm, refer to the drying procedures in the Maintenance Procedure, "Generator - Dry".

4. After the megohmmeter has been disconnected, short the exciter field leads to the generator frame. Keep these leads connected to the frame for several minutes. This will allow any voltage that has been built up to be discharged.

Exciter Armature (Rotor)

1. Disconnect the exciter armature's leads from the rotating rectifiers. Disconnect the generator field leads from the rectifier's positive heat sink. Disconnect the generator field leads from the rectifier's negative heat sink.

2. Connect the leads of the exciter armature to one clamp of a 500 volt megohmmeter. Connect the remaining lead of the megohmmeter to the shaft.

   Note: Never apply a megohmmeter to rotating rectifiers.

3. Apply 500 volts for a duration of one minute. Record the reading from the megohmmeter.

4. This reading must be a minimum of 1.0 megohm. If the reading is less than 1.0 megohm, refer to the drying procedures in the Maintenance Procedure, "Generator - Dry".

5. Disconnect the megohmmeter. Short the leads of the exciter armature to the generator frame. Keep these leads connected to the frame for several minutes. This will discharge any voltage that has built up.

Generator Field (Rotor)

1. Connect the positive lead and connect the negative lead to one clamp of a 500 volt megohmmeter. Connect the remaining lead of the megohmmeter to the shaft.

2. Apply 500 volts for a duration of one minute. Record the reading from the megohmmeter.

3. This reading must be a minimum of 1.0 megohm. If the reading is less than 1.0 megohm, refer to the drying procedures in the Maintenance Procedure, "Generator - Dry".

4. After the megohmmeter has been disconnected, short the generator field leads to the generator frame. Keep these leads connected to the frame for several minutes. This will discharge any voltage that has built up.

Generator Armature (Stator)

1. Disconnect the power connections from the generator terminals. Disconnect the control devices from the generator terminals.

2. Measure the insulation resistance of each phase separately. While this measurement is being taken, the other two phases should be shorted to ground.

3. Connect a 1000 volt megohmmeter between one of the phase leads and the generator frame.

4. Apply 1000 volts for a duration of one minute. Record the reading from the megohmmeter. Correct this reading to 40 °C (104 °F). This reading should not be less than the results of the following formula:

   1. Add 1000 to the rated generator voltage.

   2. Divide this sum by 1000.

   3. The result will be resistance in megohms.

5. After the megohmmeter has been disconnected, short the generator armature leads to the generator frame. Keep these leads connected to the frame for several minutes. This will discharge any voltage that has built up.