Frequency Control by Turbine and Governor

In power generation systems, the electrical frequency is directly related to the rotational speed of the generator. The generator, in turn, is driven by a prime mover, which is typically a turbine (such as steam turbine, gas turbine, hydro turbine, or wind turbine). To maintain a stable electrical frequency (e.g., 50 Hz or 60 Hz), the speed of the turbine must be precisely controlled.

This precise speed control is achieved by a device called a governor. The governor acts as a feedback control system. It monitors the speed of the turbine-generator unit and compares it to a desired setpoint speed. If the speed deviates from the setpoint, the governor adjusts the energy input to the turbine. For example:

• In a steam or gas turbine, the governor controls the flow of fuel or steam.
• In a hydro turbine, it controls the flow of water through the gates or valves.
• In a wind turbine, it might adjust blade pitch or control braking mechanisms.

By regulating the energy input, the governor regulates the torque produced by the turbine, thereby controlling its speed and consequently the frequency of the electricity generated.

Why Turbine and Governor Control Frequency

Let's look at why frequency is the parameter typically controlled by the turbine and governor, and why other options are less directly controlled by this system:

• Frequency: As explained, frequency is directly proportional to the generator's rotational speed, which is controlled by the turbine's speed. The governor's primary function is speed/frequency regulation.
• Voltage: Voltage is primarily controlled by the excitation system of the generator, which adjusts the strength of the magnetic field. While speed changes can affect voltage, the main control mechanism is the excitation system, not the turbine and governor.
• Current: Current is determined by the load connected to the generator and the voltage. The turbine and governor affect the system's ability to supply the power demanded by the load (which relates to current), but they don't directly control the magnitude of the current flowing.
• Power Factor: Power factor is related to the phase relationship between voltage and current, influenced by the type of load (resistive, inductive, capacitive) and the generator's excitation. It is not directly controlled by the turbine's mechanical speed regulation.

Therefore, the parameter usually controlled by a turbine and a governor is the frequency of the electrical output.