Short Answer:

The governing mechanism in turbines is a system used to regulate and maintain a constant speed of the turbine under varying load conditions. When the electrical or mechanical load changes, the turbine speed tends to fluctuate. The governing mechanism automatically adjusts the flow of water or steam entering the turbine to bring the speed back to normal.

In hydraulic turbines, this is achieved by controlling the position of the guide vanes or nozzles through a governor system. The main purpose of the governing mechanism is to ensure stable operation, protect the equipment from damage due to over-speeding, and maintain efficiency during load variations.

Detailed Explanation :

Governing Mechanisms in Turbines

The governing mechanism in turbines plays a vital role in controlling the speed of a turbine by adjusting the flow of working fluid, whether it is water (in hydraulic turbines) or steam (in steam turbines). A turbine must operate at a nearly constant speed to ensure uniform power generation and safe operation of connected machinery. When the load on the turbine changes, the flow rate of water or steam must also change to maintain this constant speed, and this is achieved through the governing mechanism.

The governing mechanism detects any change in speed and immediately responds by regulating the supply of fluid. When the load increases, the turbine slows down, and the mechanism increases the fluid supply. Conversely, when the load decreases, the turbine tends to speed up, and the mechanism reduces the fluid supply. This automatic adjustment keeps the turbine running steadily at its rated speed.

Need for Governing Mechanism

Turbines are directly connected to electrical generators, which must run at constant speed to maintain the frequency of the generated current. If the turbine speed fluctuates, it affects the power output and frequency stability. Therefore, a governing mechanism is necessary to:

Maintain constant turbine speed during load changes.
Prevent over-speeding, which can damage turbine parts.
Ensure safe and efficient operation of the turbine.
Maintain the frequency of electrical output constant.

Working Principle of Governing Mechanism

The governing mechanism works on the principle of detecting changes in turbine speed and adjusting the flow of fluid accordingly. The system generally consists of three main parts:

Speed Sensing Element (Governor):
It detects variations in turbine speed using a centrifugal mechanism (usually a flyball governor). When the turbine speed changes, the governor senses this and produces a mechanical movement proportional to the speed deviation.
Control Mechanism:
The signal from the governor is transmitted to a control valve or guide vane mechanism that adjusts the flow of fluid entering the turbine.
Servomotor or Actuator:
The servomotor receives the control signal and performs the necessary movement to open or close the valve or nozzle, thereby regulating the fluid flow to the turbine.

This entire process happens automatically and continuously to maintain steady turbine operation.

Types of Governing Mechanisms in Turbines

The governing mechanisms differ based on the type of turbine used. In general, they are classified as follows:

Governing in Pelton Turbine:
In a Pelton turbine, water strikes the buckets through one or more nozzles. The governing is done by controlling the flow through a needle valve inside the nozzle. When the load on the turbine decreases, the governor pushes the needle valve forward, reducing the water jet flow. If the load increases, the needle valve retracts to allow more water flow.
Additionally, a deflector plate is used to divert water away from the buckets during sudden load reduction to prevent over-speeding.
Governing in Francis Turbine:
In a Francis turbine, the flow of water is controlled by adjustable guide vanes (wicket gates) placed around the runner. The governor system changes the angle of these guide vanes to regulate the water entering the runner. When the load increases, the vanes open wider; when the load decreases, the vanes close to reduce water flow.
Governing in Kaplan Turbine:
The Kaplan turbine uses adjustable runner blades and guide vanes. The governing mechanism simultaneously controls both to maintain maximum efficiency. A servomotor system changes the guide vane opening and runner blade angle depending on the load variation.
Governing in Steam Turbines (for comparison):
Steam turbines use a throttle or nozzle control system where steam flow is adjusted using control valves. The principle remains similar—regulating fluid flow to maintain constant turbine speed.

Components of Hydraulic Turbine Governing System

Governor:
It senses speed variations using a centrifugal flyball system.
Oil Pressure System:
It amplifies the motion of the governor and transmits it to the servomotor.
Servomotor:
Converts oil pressure energy into mechanical motion for operating guide vanes or needle valves.
Control Valve:
Regulates the flow of oil to the servomotor based on governor action.
Linkage Mechanism:
Connects the servomotor to the guide vanes or needle valve for proper movement.

Advantages of Governing Mechanism

Maintains constant turbine and generator speed.
Protects the turbine from damage caused by over-speeding.
Improves the operational efficiency of the power plant.
Reduces mechanical stress and vibration in the system.
Ensures consistent power generation and frequency stability.

Limitations

Requires regular maintenance to ensure accurate response.
Mechanical systems may have a delay in response time.
Complex hydraulic systems can lead to leakage or operational issues if not properly maintained.

Conclusion

The governing mechanism in turbines is essential for maintaining constant speed and stable operation under varying load conditions. It automatically adjusts the water or steam supply by controlling guide vanes, nozzles, or valves to prevent over-speeding and ensure consistent performance. Depending on the turbine type—Pelton, Francis, or Kaplan—the governing method may vary, but the purpose remains the same: to provide smooth, efficient, and safe operation of the turbine and the entire power plant system.