Hydraulic Machines

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  • Topic: Turbine, Water turbine, Pelton wheel
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CHAPTER 5
TURBINES

5.1

Introduction
Hydraulic turbines are the machines which use the energy of water and convert it to

mechanical energy. The mechanical energy developed by a turbine is used in running an electric generator which is directly coupled to the shaft of the turbine. The electric generator thus develops electric power, which is known as hydro-electric power.

5.2

Elements of Hydraulic Power Plants

Fig.5.1

General Layout of a Hydraulic Power Plant

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Fig.5.1 shows a general layout of hydraulic power plant, in which an artificial storage reservoir formed by constructing a dam has been shown.

5.3

General Classification of Turbines
Turbines are hydraulic machines that convert energy into rotating mechanical energy

which in turn generators to produce electrical energy. Originally developed from the water wheels, hydraulic turbines are the prime mortars of importance in modern water power development. According to their hydraulic action, turbines are broadly divided into two classes.

(1) Impulse Turbine: Impulse turbines are more efficient for high heads. At the inlet to the turbine runner, pressure head can be completely converted into kinetic head in the form of a jet of water issuing from one or more nozzles. The free jet will be at atmospheric pressure before as well as after striking the vanes. The turbines are regulated by nozzles which may be a simple straight flow type or a deflector type. The impulse turbines are commonly represented by Pelton Wheels. Turgo turbine is also an impulse turbine but with different buckets, when compared with pelton. Turgo and cross flow turbines are relatively new developments in this class.

The main advantages of these turbines are:


They can be easily adopted to power variation with almost constant efficiency.



The penstock overpressure and the runner overspeed control are easier.



The turbine enables an easier maintenance.



Due to the jet the manufacturer of these turbines impose a better solid particle control, conducting, consequently, to a lower abrasion effect.

(2) Reaction Turbine: A turbine can be made to rotate under the action of water flowing under pressure through the runner. In such turbines the penstocks, the inlet passage to the runner, passage between the runner vanes, all form a continuous passage for the flow under a pressure which continuously decreases from inlet to outlet. The turbine runner directly converts both kinetic energy as well as the pressure energy into mechanical energy. Reaction turbines are represented in modern practice by two principal types: the Francis turbine where the flow is directed radial to the runner axis and the Propeller type

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where the flow is axial to the runner axis. Propeller turbines may be fixed blade or adjustable blade types. Kaplan turbine has adjustable blades.

The main advantages of these turbines are:


It needs lesser installation space.



It provides a greater net head and a better protection against downstream high flood levels.



It can have greater runner speed.



It can attain greater efficiencies for high power values.

In order to distinguish different turbines, the hydraulically salient features like pressure, head, flow direction and magnitude, speed and power etc. The general classification of hydraulic turbines is illustrated in Fig.5.2.

Hydraulic Turbines

Impulse Turbines

Pelton

Turgo

Reaction Turbines

Cross-Flow

Fixed -Blade

Propeller

Kaplan

Francis

Tubular

Deriaz

Bulb

Fig.5.2 General Classification of Turbines

5.4

Number of Units
It is normally cost effective to have a minimum number of units at a given small

hydropower installation. Multiple units may, however, be necessary from the operational point of view so that even one unit breaks down or is in the routine maintenance, the power generation can be achieved to a certain extent. The...
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