SPRING 6Y3940 - Caterpillar

Troubleshooting Guide
General
Before attempting to repair the SRCR Generator, be familiar with the operating principles of the generator and the applicable wiring diagrams.
Do not lower or raise the excitier assembly with generator operating. When the engine-generator is operating, do not touch the aluminum heat sink because it is electrically charged. The rectifiers can be damaged if metal contact is made between the aluminum heat sink and the generator frame.Voltages up to 230 are present on the static exciter terminal board.
Generator Rated Above 600 VoltsDo not attempt to measure line voltage or line current on generators rated above 600 volts with direct reading test metering equipment. Potential and current transformers rated for applicable voltages must be used, even though test instruments have high voltage scales. DO NOT rely on test instrument insulation alone when working on power circuits above 600 volts.
Voltage and cycles are directly proportional to RPM. A four pole, 60 cycle, 230 volt, 1800 RPM generator operating at low idle (1200 RPM) produces 153 volts at 40 cycles. When troubleshooting for voltage that is too high, a generator can usually be operated at low idle RPM (never below low idle RPM). The lower voltage produced by slow generator RPM would still be high when compared to the generator RPM. If slow generator RPM does not lower the high voltage enough, stop the electric set immediately. Excitation components can be damaged in a few seconds by the heat resulting from high voltage.Successful troubleshooting can be accomplished in a minimum of time if you:1. Recognize the apparent operational trouble.2. Diagnose the trouble from the wiring diagram and troubleshooting.3. Verify the diagnosed trouble by checking with appropriate test instruments.Keep these fundamentals in mind:1. A generator is an energy converter. It can not deliver more power than the engine driving it.2. Electric motors are energy converters. The motors automatically absorb more power if the connected load demands it. Power is a product of voltage and current. If the motor voltage is lower than normal, current input must increase proportionately.3. 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.4. Generator heating is the result of line current. The higher the line current, the greater the heat.5. A voltmeter and ammeter or a kW meter will not necessary indicate the KVA load on a generator because of the power factor of the load.6. When load testing a generator with a resistance load bank or a water barrel, load amperes for rated kilowatts at rated volts are determined by multiplying nameplate amperes by nameplate power factor. For example; a generator rated 230 volts, 157 amperes, 0.8 power factor will be fully loaded when delivering 230 volts and 125.6 amperes.7. Current will flow only through clean, solid connections. Vibration can and does loosen switchboard fasteners.8. Electrical instruments are not precisely accurate. Five percent difference in readings between two instruments is common. Multi-scale instruments can exhibit five percent difference