How does a turbine governor maintain constant speed under varying load?

• A. By adjusting the boiler pressure.
• B. By adjusting steam input through control valves based on speed deviation measured by a governor or electronic control system.
• C. By changing condenser vacuum.
• D. By altering feedwater temperature.

Answer: (B)

The key idea is feedback-based control of steam supply to keep speed steady. A turbine governor continuously compares the actual generator speed to a desired set speed and uses that speed error to adjust how much steam is admitted to the turbine. The adjustment is done through the main steam control valves under the governor (or an electronic control system) that positions the valve opening.

If load increases, the turbine would tend to slow because more mechanical power is drawn from it. The governor detects the drop in speed and opens the steam valve more, increasing steam flow to boost turbine torque and bring the speed back to the setpoint. If load decreases, the speed tends to rise, so the governor trims back steam flow by closing the valve slightly, reducing torque and lowering speed back toward the setpoint.

Boiler pressure, condenser vacuum, or feedwater temperature influence overall plant operation, but the direct mechanism for maintaining constant speed is adjusting steam input based on speed deviation measured by the governor or electronic control system.