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1. Chapter-6
Hydraulic Turbines

2. INTRODUCTION
 Water turbines are used to convert the energy of falling water
into mechanical energy.
 A water turbine is a rotary engine that converts kinetic and
potential energy of water into mechanical work.
 Water turbines were developed in the 19th century and were
widely used for industrial power prior to electrical grids. Now
they are mostly used for electric power generation.
 In hydro-electric power plants water turbines are used to convert
the energy of falling water into mechanical energy, which is
further utilized for driving the electric generators.
 The water turbines are simple in construction, highly efficient in
operation (about 90% on full load), easily controllable and pick
up the load in a very short time.

3. Classification of water turbines
The hydraulic turbines are classified based on:
 According to the direction of flow of water on moving
blades
 According to the action of water on moving blades.
 According to the head and quantity of water available
 According to the name of the originator
 According to the disposition of the turbine shaft
 According to the specific speed

4. According to the direction of flow of water on
moving blades
 According to the type of flow of water, the water turbines used
as are four types
i. Axial flow turbines having flow of water along the shaft axis
 Kaplan turbine is an axial flow turbine and has adjustable runner
blades which can be rotated about pivots fixed to the boss of the
runner.
 If the runner blades of the axial flow turbines are fixed, these are
called the propeller turbines.
ii. Inward radial flow turbines having flow of water along the
radius
iii. Tangential/peripheral flow turbines having flow of water
along the tangential directions; example Pelton wheel turbines
iv. Mixed flow (radial inlet and axial outlet) turbines
Example Francis turbine is the mixed flow turbine

5. According to the action of water on moving blades
 According to the action of water on moving blades, water
turbines are of two types, namely impulse and reaction type
turbines.
 When the entire pressure of water is converted into kinetic
energy in a nozzle and the jet thus formed drives the wheel, the
turbine is of impulse type.
 Whereas if the water pressure combined with its velocity works
on the runner the turbine is known as the reaction type turbine.
 Pelton wheel is an impulse turbine, in which the water flowing
over the turbine rotor blades remains constant.
 In reaction turbines, the rotor of the turbine operates while
submerged in water, the turbine casing being full of water. As the
water flows through the rotor blades its pressure changes.
 Francis turbines, Kaplan turbines and propeller turbines are
reaction turbines.

6. According to the head and quantity of water available
 According to the head and quantity of water available, the water
turbines are of two types.
 high head and low flow
 Low to medium head and high to medium discharge turbines.
According to the name of the originator
 According to the name of originator, water turbines are of three
types, namely Pelton wheel, Francis turbine and Kaplan turbine.
 Pelton wheel is an impulse turbine and is suited to high head and
low flow plants.
 Francis turbine is a reaction turbine and is suited to medium
head and medium flow plants. Kaplan turbine is a special type of
propeller turbine having adjustable blades and is suited to low
head and high flow plants.

7. According to the disposition of the turbine shaft
 Horizontal shaft turbine-
 Vertical shaft turbine.
According to the specific speed
 The specific speed of the turbine is defined as the speed of a
geometrically similar turbine that would develop one metric
horse power under a head of one meter.
 All geometrically similar turbines (irrespective of their sizes)
have the same specific speed when operating under the same
conditions of head and flow.
Where as Ns is the specific rotational speed in metric units.
N is the actual rotational speed of turbine in rpm
P is output in metric hp and
H is the effective head in metres.

8. Hydraulic Turbines
 The following factors have the bearing on the selection
of the right type of hydraulic turbine.
 Rotational Speed
 Specific Speed
 Maximum Efficiency
 Part Load Efficiency
 Head
 Type of Water
 Runaway Speed
 Cavitation
 Number of Units
 Overall Cost.

9. Types Hydraulic Turbines
1. Reaction turbines, where the turbine is totally embedded in the
fluid and powered from the pressure drop across the device
 Derive power from pressure drop across turbine
 Totally immersed in water
 Angular & linear motion converted to shaft power
 Angular & linear motion converted to shaft power
 Propeller, Francis, and Kaplan turbines
2. Impulse turbines, where the flow hits the turbine as a jet in an
open environment, with the power deriving from the kinetic
energy of the flow.
 Convert kinetic energy of water jet hitting buckets
 No pressure drop across turbines
 Pelton, Turgo, and crossflow turbines

10. Francis turbine
 is used for low to medium heads.
 It consists of an outer ring of stationary guide blades fixed to
the turbine casing and an inner ring of rotating blades forming
the runner.

11. Cont’…
 The guide blades control the flow of water to the
turbine.
 Water flows radially inwards and changes to a
downward direction while passing through the
runner.
 As the water passes over the “rotating blades” of the
runner, both pressure and velocity of water are
reduced. This causes a reaction force which drives
the turbine

12. Kaplan turbine
 is used for low heads and large quantities of water.
 It is similar to Francis turbine except that the runner of Kaplan
turbine receives water axially.
 Water flows radially inwards through regulating gates all
around the sides, changing direction in the runner to axial
flow. This causes a reaction force which drives the turbine.

13. Propeller Turbine
 The propeller runner may be considered as a development of a
Francis type in which the number of blades is greatly reduced
and the lower band omitted.
 It is axial flow turbine having a small number of blades from
three to six.
 has high efficiency at full load but its efficiency rapidly drops
with decrease in load.

14. Cont’…
Hydraulic head
 Hydraulic head are two types:
 GROSS HEAD of a hydropower facility is the difference
between head water elevation and tail water elevation.
 NET HEAD is the effective head on the turbine and is equal to
the gross head minus the hydraulic losses before entrance to the
turbine and outlet losses.
 Hydraulic head losses are caused by mainly Frictional losses
(losses in the closed and open pipe systems)