Basic Mechanical Engineering- Hydraulic turbines

HYDRAULIC
TURBINES

Prepared by,

M.S.Steve,
Assistant Professor,
Amal Jyothi College of Engineering
Email: msstevesimon@gmail.com

DEFINITION
• Hydraulic turbine – A rotary engine that
converts hydraulic energy into mechanical
energy.
• Mechanical energy is used in running an
electric generator which is coupled to turbine
shaft.

M.S.Steve/ 9745917858/msstevesimon@gmail.com

CLASSIFICATION OF
TURBINES
• According to the type of energy at inlet
Impulse turbine
Reaction turbine


…(1)

IMPULSE TURBINE
• Energy available at the inlet of the turbine is
only kinetic energy.
• Pressure is atmospheric from inlet to outlet.
• Works on the basis of impulse momentum
principle
• Eg: Pelton Wheel


PELTON WHEEL OR
PELTON TURBINE

..(1)

• Named after American Engineer L.A.Pelton
• Energy available at inlet is only kinetic energy.
• Used for high heads.


PELTON WHEEL

..(3)

• Water from reservoir flows through penstocks.
• At the outlet of penstock nozzle is fitted.
• Nozzle converts hydraulic energy of water into kinetic
energy.
• Water striking the nozzle is controlled using a spear.
• Water comes out as a jet from nozzle and strikes the
buckets (vanes) which are fixed on the periphery of a
wheel.
• Casing is used to prevent splashing of water.

PELTON WHEEL
..(4)

Double cup shaped
Runner bucketsCast steel or
Bronze

REACTION TURBINE
• Energy of fluid partly transferred into kinetic
energy before it enters the runner
• It enters the runner with excess pressure.
• Pressure energy is converted into kinetic energy as
water passes through runner.
• The difference in pressure between inlet and outlet
of runner (reaction pressure) is responsible for
motion of runner.
• Eg: Francis turbine, Kaplan Turbine

FRANCIS TURBINE

…1

• Named after American Engineer
J.B.Francis
• It is a mixed flow reaction turbine with
medium head and medium specific speed

FRANCIS TURBINE COMPONENTS

•
•
•
•
•
•
•

Penstock
Scroll/Spiral casing
Speed ring/Stay ring
Stay vanes
Guide vanes/Wicket vanes
Runner blades
Draft tube

FRANCIS TURBINE-WORKING
• Water from the penstock enters the scroll casing
which completely surrounds the runner.
• Involute casing provides an even distribution of
water(constant velocity) around the circumference of
the runner.

• Stay rings directs water from scroll casing to guide
vanes.

FRANCIS TURBINE-WORKING
• The guide vanes
-regulate the quantity of water supplied to the
runner(to take care of the load variations)
-direct water to the runner at an appropriate angle.
• The runner consists of a series of curved vanes evenly
arranged around the circumference.
• At the entrance to the runner only a part of energy of
water is converted into kinetic energy and substantial
part remains in the form of pressure energy.
• As water flows through the runner the change from
pressure to kinetic energy takes place gradually.

FRANCIS TURBINEWORKING
• The difference in pressure between the inlet and
outlet of the runner is called reaction pressure.

• Water enters the runner from the guide vanes
towards the centre radially and discharges out

axially- Mixed flow turbine.
• After doing work water is discharged to the tail
race through a closed tube of gradually enlarging
section called draft tube.

KAPLAN TURBINE

…1

• Developed by Austrian Engineer
V. Kaplan.
• Suitable for relatively low heads and requires
large volume of water to develop large power.
• Kaplan turbine is a reaction turbine in which
water enters and leaves the runner blades
axially-Axial flow turbine

KAPLAN TURBINE- COMPONENTS
Scroll casing
Guide Vanes
Runner Vanes
Draft tube

KAPLAN TURBINECOMPONENTS

...2

• The shaft of an axial flow reaction turbine is
vertical.
• The lower end of the shaft is made bigger and
is known as hub or boss.
• The runner vanes are fixed on the hub or boss.


KAPLAN TURBINE- WORKING
• Kaplan turbine works on the reaction principle
as Francis turbine.
• Only difference is that water enters and leaves
the turbine axially – Axial flow turbine.
• Both the guide vane(wicket gate) angle and
runner vane angle can be adjusted which gives
rise to high efficiency.

Classification of Hydraulic
Turbines.
• Based on action of water
• Based on the main direction of flow
• Based on the head and quantity of water
required.
• Based on the specific Speed

Classification based on direction of Flow
• Tangential flow: Pelton Turbine
• Axial Flow Turbine: Kaplan Turbine

• Radial Flow Turbine:
Inward: Thomson Turbine
• Mixed Flow Turbine : Modern Francis Turbine

Classification Based on Head Available
High Head Turbine(High head & low discharge)
Head ranges from several hundred to thousand meters
e.g. Pelton Turbine(250 to 2000m)
Medium head Turbine(Medium head and medium discharge)
Head ranging from 50m to 250m
e.g. Modern Francis Turbine

Low Head Turbine(low head high discharge)
Head less than 50m
e.g. Kaplan Turbine , propeller turbine

Specific speed of Turbine
• It provides the means of comparing the speed
of all type if turbine on the same basis of head
and power.
• Specific speed of a turbine is defined as the
speed at which turbine run developing unit
power under unit head .


SPECIFIC SPEED
…1

• Speed of a geometrically similar turbine that would
develop 1 kW power when working under a head of
1 m. (in SI system)
• All geometrically similar turbines will have the same
specific speed when operating under the same head,
irrespective of its size.
• Specific speed of a turbine is obtained using

NS

N P
H 5/ 4

Where Ns=Specific speed ,N = speed in rpm
H=effective head in m ,P= Power output in kW

CLASSIFICATION OF TURBINE BASED ON
SPECIFIC SPEED
• According to the specific speed of the turbine
High specific speed turbine
Medium specific speed turbine
Low specific speed turbine

HIGH SPECIFIC SPEED
TURBINE
• A turbine of higher specific speed will have a higher speed
of rotation of the turbine runner
• So a small diameter runner can develop high peripheral
velocity
• It allows reduction in runner diameter as well as the overall
size of the runner for a given head and power output.
• It will further reduce the weight and cost of the runner.

• Hence high specific speed turbines are used for low head
applications like Kaplan turbine.(255-860)

MEDIUM SPECIFIC SPEED
TURBINES
• Francis turbine has medium range of specific
speed
• Its value ranges from 50 to 340 in SI units for
a Francis turbine


LOW SPECIFIC SPEED TURBINES
• Low specific speed turbines are used for high
head turbines
• A runner of too high specific speed with high
available head will increase the cost of the
turbine on account of the high mechanical
strength required
• Eg: Pelton turbine(8.5 to 30)

Selection of turbines
Type of turbine

Range of head

Specific speed in metric
units

Pelton

200-2000

10-15

Francis

15-300

80-420

Propeller

5-30

310-1000

Basic Mechanical Engineering- Hydraulic turbines

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