What device automatically controls the speed of a steam turbine?

• A. Governor valve
• B. Throttle valve
• C. Safety valve
• D. Control relay

Answer: (A)

Automatic speed control of a steam turbine is accomplished by the governor, which senses how fast the turbine is turning and automatically adjusts the steam input to keep that speed constant. The governor valve is the part of this system that actually modulates how much steam enters the turbine. When load increases and speed tends to drop, the governor opens the valve to admit more steam, restoring speed. When load decreases and speed tends to rise, it closes the valve to reduce steam flow. The throttle valve sets the flow of steam, but it is controlled by the governor, not by itself, so it wouldn’t maintain speed on its own. The safety valve prevents overpressure, not speed, and the control relay is part of the electrical control system rather than the primary automatic speed regulator.