How is generator output controlled?

Generator output is primarily controlled by adjusting field excitation. In a generator, especially in synchronous generators, the output voltage and reactive power can be regulated by altering the amount of excitation current supplied to the rotor winding. When the field excitation is increased, the magnetic field strength around the rotor increases, leading to a higher induced output voltage. Conversely, if the excitation is decreased, the output voltage will drop. This ability to control the field excitation provides a direct means to manage the output characteristics of the generator, allowing operators to ensure that the generated voltage remains stable regardless of load changes.

Adjusting the speed of the rotor affects the frequency of the generated voltage and is a method more relevant for certain types of generators, particularly in prime mover-driven systems, but it does not directly control the output in the same way as varying field excitation. Modifying load resistance influences the current drawn from the generator but does not inherently control the generator's output characteristics. Additionally, using a variac transformer can adjust voltage levels but is not a method used for controlling generator output directly in the context of adjusting the excitation system.