What is the purpose of 'automatic voltage regulation' (AVR) in a ship's generator?

The purpose of automatic voltage regulation (AVR) in a ship's generator is to maintain a stable and consistent output voltage despite variations in load and prime mover speed. A stable voltage is essential for the proper operation of all electrical equipment connected to the generator. When the load on the generator increases, the output voltage tends to decrease due to the increased current flow and the generator's internal impedance. Conversely, when the load decreases, the output voltage tends to increase. The AVR automatically adjusts the generator's excitation current to compensate for these load variations and maintain a constant output voltage. The AVR works by monitoring the generator's output voltage and comparing it to a reference voltage. If the output voltage is too low, the AVR increases the excitation current, which strengthens the magnetic field and increases the generated voltage. If the output voltage is too high, the AVR decreases the excitation current, which weakens the magnetic field and decreases the generated voltage. This feedback loop continuously adjusts the excitation current to maintain the output voltage within a narrow tolerance band. Some AVRs also compensate for variations in prime mover speed, ensuring that the output voltage remains stable even when the engine speed fluctuates. By maintaining a stable voltage, the AVR protects electrical equipment from damage due to overvoltage or undervoltage and ensures reliable operation of the ship's electrical system.