Governing of Turbines

1. Introduction

Governing of turbines is the process of maintaining a constant speed of the turbine runner despite variations in load.

• When load on the generator decreases, turbine speed tends to increase
• When load increases, turbine speed tends to decrease

The governing system automatically adjusts the flow of water to maintain constant speed.

2. Necessity of Governing

Governing is essential because:

• Electrical generators require constant speed to maintain frequency
• Prevents over-speeding (which may damage turbine)
• Ensures stable and safe operation
• Improves efficiency and performance

3. Principle of Governing

The governing system works on a feedback mechanism:

1. Load change occurs
2. Speed of turbine changes
3. Governor detects speed variation
4. Control mechanism adjusts water flow
5. Speed returns to normal

4. Components of Governing System

Main Parts:

• Governor (speed-sensing device)
• Servomotor (amplifies control signal)
• Control valve or guide vane mechanism
• Oil pressure system (in modern turbines)

5. Types of Governing

(A) Governing of Pelton Turbine

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Pelton turbine is an impulse turbine, so governing is done by controlling the jet of water.

Methods:

(i) Needle Regulation

• A needle (spear) is placed inside the nozzle
• Moves forward/backward to control jet flow
• Reduces or increases discharge

(ii) Deflector Method

• A deflector plate temporarily diverts the jet
• Prevents sudden speed rise
• Used during rapid load decrease

(B) Governing of Francis Turbine

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Francis turbine is a reaction turbine.

Method: Guide Vane Regulation

• Flow is controlled by wicket gates (guide vanes)
• Vanes open/close to regulate water flow
• Controlled by a servomotor and governor system

(C) Governing of Kaplan Turbine

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Kaplan turbine is also a reaction turbine.

Double Regulation System:

1. Guide vane control (like Francis turbine)
2. Runner blade pitch control

• Blades adjust angle automatically
• Ensures high efficiency at varying loads

6. Types of Governors

(a) Mechanical Governor

• Uses centrifugal force
• Example: Flyball governor

(b) Hydraulic Governor

• Uses oil pressure system
• Common in modern turbines

(c) Electronic Governor

• Uses sensors and control systems
• Highly accurate and fast response

7. Working of Hydraulic Governor

1. Speed change is detected by governor
2. Oil flow is directed to servomotor
3. Servomotor moves control mechanism
4. Water flow is adjusted
5. Speed is restored

8. Important Terms

(a) Speed Regulation

$$\text{Speed Regulation} = \frac{N_{no\ load} – N_{full\ load}}{N_{full\ load}} \times 100$$

• Lower value indicates better governing

(b) Stability of Governing

• Ability to maintain steady speed without oscillations

(c) Sensitivity

• Ability to respond to small speed changes

9. Comparison of Governing Methods

Turbine Type	Governing Method	Control Element
Pelton	Needle & Deflector	Jet control
Francis	Guide Vanes	Wicket gates
Kaplan	Guide Vanes + Blades	Double regulation

10. Advantages of Proper Governing

• Maintains constant frequency
• Prevents mechanical damage
• Improves efficiency
• Ensures smooth operation

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