Which governing method maintains a constant speed at all loads?

Isochronous governing is the method that maintains a constant speed regardless of the load changes on the system. In this type of governing, the governor adjusts the fuel supply automatically to keep the speed of the engine or turbine constant, even when there are fluctuations in load. This control is crucial in applications where stability and performance at a fixed speed are critical, such as in synchronous generators operating in parallel with other units.

In contrast, speed droop governing allows for a deliberate reduction in speed with increased load. Although this method is beneficial in scenarios where multiple generators are connected to a common bus, it does not maintain a fixed speed under varying load conditions.

Nozzle governing and throttle governing are other control methods typically used in specific contexts, primarily in steam or gas turbines. These methods adjust fuel flow but do not inherently aim to maintain a constant speed at all loads like isochronous governing does. Instead, they allow for speed variations in response to load changes, thus making them unsuitable for maintaining a constant speed under all circumstances.