Short Answer:

A governing mechanism in turbines is a system used to control the speed of the turbine by regulating the flow of water entering it. It automatically adjusts the water supply according to the load on the turbine. When the load decreases, the governing mechanism reduces the water flow, and when the load increases, it allows more water to maintain a constant speed. This ensures stable operation and prevents speed fluctuations in the turbine during load variations.

The governing mechanism helps maintain the desired speed, ensures smooth working, and prevents damage caused by sudden changes in load or speed.

Detailed Explanation :

Governing Mechanism in Turbines

The governing mechanism in turbines is a vital control system designed to maintain a constant speed of the turbine, even when the load on it changes. In hydroelectric power plants, the turbine drives a generator that must run at a constant speed to produce electricity of a fixed frequency. However, due to varying demands on the electrical load, the torque on the turbine changes. The governing mechanism automatically adjusts the water flow to ensure that the turbine speed remains constant, thereby maintaining efficient and safe operation.

1. Need for Governing Mechanism:
   In a turbine, water energy is converted into mechanical energy. The turbine runs at a specific speed required to maintain the generator’s frequency (for example, 50 Hz in India). When the load on the generator changes, the speed of the turbine tends to vary:

• If the load decreases, the turbine speed increases due to excess water flow.
• If the load increases, the turbine speed decreases because of insufficient water flow.

To maintain constant speed under all conditions, the governing mechanism is employed to control the flow of water automatically and maintain equilibrium between load and water supply.

2. Function of the Governing Mechanism:
   The main function of a governing mechanism in a turbine is to regulate the flow of water entering the turbine according to the load condition. Its key objectives are:

• To keep the turbine speed constant under varying load.
• To maintain stable frequency of the electric power generated.
• To prevent damage to the turbine or generator due to overspeed.
• To improve the overall efficiency and safety of the hydroelectric system.

Thus, it acts as an automatic control system that balances load and speed through water flow regulation.

3. Working Principle of Governing Mechanism:
   The governing mechanism operates on the principle of feedback control. It detects any change in turbine speed and automatically adjusts the position of flow-controlling devices (such as nozzles, guide vanes, or wicket gates) to correct the speed deviation.

When the turbine speed changes, a governor senses the variation through centrifugal force or hydraulic control. The governor then sends a signal to the servomotor or hydraulic actuator, which adjusts the water inlet device.

• If the turbine runs faster than normal, the governor decreases the water flow.
• If the turbine runs slower, it increases the water flow.

This continuous adjustment helps the turbine maintain a constant speed regardless of load fluctuations.

4. Components of Governing Mechanism:
   The governing system consists of several mechanical and hydraulic parts that work together for smooth regulation:

• Governor: The main controlling device that senses speed changes using centrifugal force.
• Oil Pump: Supplies oil under pressure to operate the servomotor.
• Servomotor or Hydraulic Actuator: Converts oil pressure into mechanical movement to adjust guide vanes or nozzles.
• Control Valve: Regulates the oil flow to the servomotor based on the governor’s command.
• Linkage System: Connects the servomotor movement to the turbine’s water control device.

All these parts function together to control the amount of water entering the turbine.

5. Types of Governing Mechanisms:
   The governing mechanism varies based on the type of turbine used. The main types are:

• For Impulse Turbines (e.g., Pelton Wheel):
  The governing mechanism controls the nozzle opening and hence the jet of water striking the buckets. A spear valve or needle valve is moved by the servomotor to increase or decrease water flow. Sometimes, a deflector plate is used to divert the jet temporarily to prevent overspeed during load rejection.
• For Reaction Turbines (e.g., Francis and Kaplan Turbines):
  In these turbines, the governing mechanism controls the guide vanes or wicket gates to adjust the amount of water entering the runner. In Kaplan turbines, both guide vanes and runner blades may be adjusted for efficient operation under varying loads.

6. Operation under Different Load Conditions:

• When Load Increases:
  The turbine slows down. The governor senses this reduction in speed, opens the control valve, and allows more oil to the servomotor, which opens the guide vanes or nozzle. More water enters, restoring the speed.
• When Load Decreases:
  The turbine speed increases. The governor reduces oil flow to the servomotor, which closes the guide vanes or nozzle, reducing water flow and maintaining normal speed.

This automatic control process ensures smooth operation and constant turbine speed.

7. Advantages of Governing Mechanism:

• Maintains constant speed and frequency.
• Prevents damage due to overspeeding.
• Ensures stable and efficient power generation.
• Reduces manual control and improves reliability.
• Increases the lifespan of turbine components.

8. Example of Hydraulic Governing:
   In a Pelton turbine, when load decreases, the deflector first diverts the water jet away from the buckets to reduce impact suddenly, while the spear valve gradually reduces the flow. This combination prevents water hammer and sudden speed variations. Similarly, in a Francis turbine, the guide vane angles are adjusted smoothly to regulate flow.

Conclusion:

The governing mechanism in turbines is a crucial control system that maintains constant turbine speed under varying load conditions. It works automatically by adjusting the water flow through the turbine. Depending on the turbine type, it may control nozzles, guide vanes, or runner blades. This mechanism ensures the stable operation, efficiency, and safety of hydroelectric power plants by keeping the speed and power output consistent. Without an effective governing system, the turbine and generator could suffer from instability and mechanical failures.