Reasons for Overvoltage Or Undervoltage in AC Diesel Generator

For Undervoltage:

1. Low Engine Speed (RPM): The most common cause. Engine not running at rated speed.

2. Faulty AVR (Automatic Voltage Regulator): AVR is failing to supply sufficient excitation current.

3. Overloading: Connected load exceeds the generator's capacity.

4. Poor Connections: Loose or corroded wiring in the output circuit causing voltage drop.

5. Failing Rotating Diodes: Diodes are weak or shorted, reducing excitation.

6. Brush/Slip Ring Issues: Dirty or pitted slip rings, worn brushes causing high resistance.

For Overvoltage:

1. Faulty AVR: AVR is defective and supplying excessive excitation current.

2. High Engine Speed (RPM): Engine governor malfunction, causing it to run too fast.

3. Loss of Load: A sudden large load disconnection can cause a temporary voltage spike.

4. AVR Sensing Circuit Fault: Poor connection in the voltage sensing wires, so the AVR doesn't "see" the correct output voltage.