Short Answer:

Governing of turbines is the process of controlling the speed of a turbine by regulating the amount of steam or working fluid entering it. It ensures that the turbine runs at a constant speed even when the load on the turbine changes. Governing helps maintain steady operation and prevents damage due to overspeed or sudden load variations.

In simple terms, turbine governing automatically adjusts the steam supply according to the load demand. When the load increases, more steam is allowed into the turbine, and when the load decreases, the steam supply is reduced to maintain a stable speed and safe operation.

Detailed Explanation :

Governing of Turbines

Governing of turbines refers to the system or mechanism used to control the flow of steam to the turbine in order to maintain a constant speed under varying load conditions. In practical power systems, the demand for electricity changes continuously, which affects the load on the turbine. If the steam flow remains constant, any decrease in load will cause the turbine to overspeed, while an increase in load will cause it to slow down.

To avoid these fluctuations and ensure stable operation, a governing mechanism is used. The governor automatically senses the change in speed and adjusts the steam supply accordingly. Thus, the governing system plays a key role in the safe, efficient, and stable operation of a turbine.

Need for Governing

To maintain a constant turbine speed under varying load conditions.
To prevent mechanical damage due to overspeed.
To ensure steady and reliable power output.
To improve efficiency and fuel economy.
To ensure synchronization with other turbines or generators in power plants.

Working Principle

The working principle of turbine governing is based on the automatic control of the steam supply. When the load on a turbine decreases, the turbine tends to run faster due to the reduced opposing torque. The governor detects this speed increase and reduces the steam supply. Conversely, when the load increases, the turbine speed drops, and the governor increases the steam flow to restore the normal speed.

This is achieved using a governor mechanism, which consists of speed-sensing elements (such as centrifugal governors), control valves, and linkages that regulate the position of the steam valve based on the turbine’s speed.

Types of Governing of Turbines

The governing of turbines can be classified into three main types depending on how the steam flow is controlled:

Throttle Governing

In throttle governing, the flow of steam to the turbine is controlled by a throttle or regulating valve located in the main steam pipe. The position of this valve is adjusted by the governor based on speed variations.

When the load decreases and turbine speed increases, the governor partially closes the throttle valve, reducing the steam flow.
When the load increases and the turbine slows down, the valve opens wider to allow more steam.

Features:

Simple construction and easy operation.
Commonly used in small and medium-sized turbines.
Steam pressure before entering the turbine is reduced when the valve closes, leading to a small loss in efficiency.

Disadvantage:

Throttle governing slightly reduces efficiency because of throttling losses due to partial pressure drop.

Nozzle Governing

In nozzle governing, instead of throttling the steam pressure, the number of nozzles admitting steam to the turbine is varied. The steam always enters at full boiler pressure, but only a portion of the nozzles are opened depending on the load.

At full load, all nozzles are open, allowing maximum steam flow.
At partial loads, some nozzles are closed, reducing the amount of steam entering the turbine.

Features:

Efficiency is higher than throttle governing because the steam always expands at full pressure.
Used in large impulse turbines such as the Curtis or Rateau turbines.
Requires more complex control mechanisms to open and close the nozzles.

Advantages:

Reduces throttling losses.
Improves part-load efficiency.

Disadvantages:

Mechanically more complicated and expensive than throttle governing.

By-pass Governing

In by-pass governing, a portion of the steam is allowed to bypass certain turbine stages during overload conditions. This method is mainly used in large reaction turbines.

When the load suddenly increases, the governor opens a by-pass valve that allows additional steam directly to the later stages of the turbine.
Once the load stabilizes, the valve closes, and normal operation continues.

Features:

Prevents sudden pressure drops in the earlier stages.
Maintains turbine efficiency during overloads.
Mainly used in modern high-capacity power plant turbines.

Advantages:

Provides smooth control during load fluctuations.
Prevents mechanical stress on turbine components.

Disadvantages:

More complex and expensive to design.

Essential Components of Governing System

Governor (Speed Sensor): Detects changes in turbine speed and sends control signals.
Linkages and Control Rods: Transmit motion from the governor to the steam valve.
Steam Control Valve: Regulates the flow of steam into the turbine.
Oil Servomotor (in modern systems): Uses hydraulic pressure to operate the steam valve smoothly.

In modern turbines, electronic and hydraulic governing systems are used for precise control and faster response compared to mechanical governors.

Functions of Governing System

Maintains constant turbine speed.
Prevents over-speeding and under-speeding.
Balances power generation with load demand.
Ensures safe turbine operation.
Reduces mechanical wear and energy losses.

Conclusion

In conclusion, the governing of turbines is a vital control mechanism that ensures the turbine operates at a constant speed under varying loads. It regulates the amount of steam entering the turbine to match the power demand, maintaining safety and efficiency. Different types of governing systems—throttle, nozzle, and by-pass—are used depending on the size and type of turbine. Modern governing systems use advanced hydraulic and electronic controls for smooth, accurate, and reliable operation. Without proper governing, turbines would face instability, mechanical stress, and operational hazards.