Hydraulic Turbines - Online Article

Introduction

Turbines are defined as the hydraulic machines which convert hydraulic energy(energy possessed by water) into mechanical energy.This mechanical energy is used in running an electric generator which is directly coupled to the shaft of the turbine. Thus the mechanical energy is converted into electrical energy.At present the generation of hydro electric power is the cheapest as compared by the power generated by other sources such as coal,oil etc. In many pumping applications, the liquid remains a higher pressure even after it has completed its utility in the process and has to be brought down to a lower pressure before further processing. the conventional method is to pass through a pressure reducing valve to effect the required pressure drop. Instead of losing the capacity of the high pressure liquid to do work, the same can be passed through a in operating a process equipment - say a pump.

Definition of Heads

1) Gross Head

The difference between the head tail race level and tail race level when no water is flowing is known as gross head.
Note: "Tail race which is a channel which carries water away from the turbines after the water has worked on the turbines".

2) Net Head

It is also called effective head and may be defined as the head available at the inlet  of the turbine.when water is flowing from head race to the turbine ,a loss of head due to friction between the water and penstocks occurs.
NET HEAD = GROSS HEAD-LOSS OF HEAD DUE TO FRICTION BETWEEN PENSTOCKS AND WATER.         

Friction loss = 4f*L*v^2/(D*2g)
V=velocity of flow in penstock.
L=length of penstock.
D=diameter of penstock.

Definitions Of Efficiencies Of A Turbine

1) Hydraulic Efficiency

It is defined as the ratio of power given by water to the runner of a turbine to the power supplied by the water at the inlet of the turbine.
HYDRAULIC EFFICIENCY=power delivered to runner/power supplied at inlet.

2) Mechanical Efficiency

It may be defined as the ratio of power delivered by water to the runner of a turbine to the power available at the shaft of the turbine.

MECHANICAL EFFICIENCY=power at the shaft of the turbine/power delivered by water to the runner.

3) Volumetric Efficiency

It may be defined as the ratio of volume of water actually striking the runner to the volume of water supplied to the turbine.

Volumetric Efficiency= volume of water actually striking the runner/ volume of water supplied to the turbine.

4) Overall Efficiency

It may be defined as the ratio of volume available at the shaft of the turbine to the power supplied at the inlet of the turbine.

OVERALL EFFICIENCY= volume available at the shaft of the turbine/ power supplied at the inlet of the turbine.

Classification Of Hydraulic Turbines

Hydraulic turbines are classified as follows

1) According to the type of energy at inlet

a) Impulse Turbine
b) Reaction Turbine

2) According to the direction of flow through runner

a) Tangential Flow Turbine
b) Radial Flow Turbine
c) Axial Flow Turbine
d) Mixed Flow Turbine

3) According to the head at the inlet of the turbine

a) High Head Turbine
b) Medium Head Turbine
c) Low Head Turbine

4) According to the specific speed of the turbine

a) Low Specific Speed Turbine
b) Medium Specific Speed Turbine
c) High Specific Speed Turbine

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Comments

Pradeep Gupta on 2008-08-09 03:45:10 wrote,

nice matter