Troubleshooting for generators

SYMPTOM

POSSIBLE CAUSE

TEST AND REMEDIES

Low Voltage

(No Load)

AVR “Volts” adjust incorrectly set.

Adjust control CLOCKWISE to increase voltage. If remote hand trimmer fitted, adjust in conjunction with trimmer.

Faulty AVR.

Replace AVR and re-test.

High Voltage

(No Load)

AVR “Volts” adjust or remote trimmer incorrectly set.

Check and adjust as necessary.

Low sensing supply from main stator.

Check sensing supply with Gen. running at nominal voltage, the sensing supply should be between 190-240 volts.

Faulty AVR.

Replace AVR and re-test.

Unstable Voltage (No Load)

AVR stability control incorrectly adjusted.

Adjust stability clockwise until voltage stabilizes. Check again on load.

Loose or corroded connection.

Check push on terminals on AVR. Check aux terminals for loose connections.

Intermittent earth on machine.

Megger all windings, include Exciter Stator, low insulation resistance can effect the AVR.

Unbalance Voltage (No Load)

Fault in main stator winding.

Disconnect all external leads to Generator and re-test. A winding short will get hot, and engine will sound slightly loaded. Shut down set and check by hand for hot spots.

No Voltage (No Load)

Loose, broken or corroded connections.

Check all auxiliary terminals. Check the AVR, push on terminals for tightness. Repair or renew where necessary.

Fault PMG, stator or Rotor.

Disconnect the PMG leads from AVR. Check voltage across leads with the set running at correct speed.

Insulation failure to earth on permanent magnet stator.

Disconnect leads and “Megger” test to earth.

Main Rectifier diodes short circuit.

Check diodes.