ROD AS 7J9863 - Caterpillar

Troubleshooting
General
Do not open or close the exciter with the engine-generator operating. When the generator is operating, the heat sinks and exciter parts are electrically charged. Components will be damaged if a metal contact is made between the generator frame and the heat sinks or exciter parts.
A large percentage of reported electrical faults result from undetected mechanical deficiencies. Take time to examine the entire installation carefully and methodically. Separate mechanical from electrical deficiencies.A generator is essentially a constant speed device. RPM that is 5 to 10 percent above or below rated rpm can cause large variations in terminal voltage.Generator heating is the result of line current; the higher the line current, the greater the heat.A voltmeter and ammeter or kW meter will not necessarily indicate the KVA load on a generator because of the power factor of the load.Before attempting to repair the generator, be familiar with the operating principles of the generator.Recognize the apparent operational trouble and diagnose the trouble from the wiring diagram and troubleshooting guide.When troubleshooting for voltage, a generator can usually be operated at a low rpm. Voltage and cycles are directly proportional to rpm. A six pole, 60 cycle, 230 volt, 1200 rpm generator operating at a low idle of 900 rpm produces 173 volts at 45 cycles. For information on the electrical and mechanical characteristics of sRCR generators, make reference to the section INDUSTRIAL DIVISION DATA SHEETS; No. 70.0 and TECHNICAL INFORMATION FILE (TIF).Test Instruments
A Volt-Ohm-Milliammeter having scales of approximately the following values:AC Volts ... 0 to 12, 0 to 100, 0 to 300DC Volts ... 0 to 50, 0 to 100, 0 to 150Ohms ... x 1, x 10, x 100, x 1000DC Amps ... 0 to 3A Kelvin or a Wheatstone Bridge is used to measure the resistance of either the generator revolving field or the stator winding.A 500 or 1000 Volt Megohmmeter is used to measure the generator stator and revolving field insulation resistance.A DC Ammeter with appropriate ampere shunt.A tong-type Volt Ammeter with scales 0 to 600 volts and 0 to 600 amperes. Some generators are rated higher than 600 amperes, but these are normally connected with two or more conductors per phase. To measure line current for these generators, measure the current in each conductor per phase and add the individual conductor currents. See if generator is rated over 600 volts.A direct reading Tachometer or a 3 or 5 second intergrating tachometer is a relatively precise indicator, providing the drive does not slip. When precise frequency control is required, a direct comparison with utility power can be made.
On generators rated above 600 volts, do not use direct reading test equipment to measure line voltage or line current (even though the instruments have high voltage scales). Potential and current transformers rated for applicable voltage must be used. DO NOT rely on test instrument insulation alone when working on power circuits above 600 volts.
Electrical instruments are not precisely accurate. Five percent difference in reading between two instruments is common. Multi-scale