When a load surge is experienced, eg when a ship’s cargo lifting equipment picks up heavy cargo, the generator voltage dips as a result. Similarly, load shedding will result in a generator overvoltage. In other words, on board, there is no such thing as a constant load. Therefore, a continuously fluctuating generator voltage must be regulated. The Automatic Voltage Regulator (AVR) regulates the generator’s output voltage by regulating the voltage of the main field (rotor’s winding).
This particular device ensures that the voltage is maintained within the required range and rapidly corrects any voltage deviations caused by load dips and shedding. In addition to regulating the generator voltage, the AVR circuitry includes protective features to ensure safe and reliable control of the generator.
Modern AVRs consist of high-quality electronic components. The components are usually cast with epoxies, which protect against high temperatures, moisture, and vibration.
A replacement AVR, if required, must be installed in accordance with the manufacturer’s installation requirements.
If the generator produces either no voltage or fluctuating voltages, try to locate the problem. Check all connectors and cables in the terminal box and the exciter components for secure connections.
While tracing a problem with an AVR and/or excitation system, the following checks can be carried out.
|Fault description||Action suggested|
|No voltage build-up when starting set||Follow separate excitation or residual voltage tests|
|Loss of voltage when set running||First stop and re-start set|
If there is no voltage or the voltage collapses after a short time, follow the separate excitation test procedure
|Generator voltage high followed by collapse||Check sensing leads to AVR. Check isolating transformer secondary output – refer to the separate excitation test procedure|
|Voltage unstable, either on no-load or with load||Check speed. If correct, check the voltage stability setting. Refer to the load testing procedure from the manufacturer|
|Voltage low on load||Check speed. If correct, check the voltage stability setting. Refer to the load testing procedure from the manufacturer|
|Phase voltages unbalanced||Check stator winding and cables to the main circuit-breaker|
|Excessive voltage/speed dip on load switching||Check governor response and P-droop adjustment for the governor|
|Sluggish recovery on load switching||Check governor response and P-droop adjustment for the governor|