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1. Water Turbines
Hydraulic machines
Hydraulic machines are defined as those machines which convert either
hydraulic energy (energy possessed by water) into mechanical energy or
mechanical energy into hydraulic energy.
TURBINES
Turbines arc defined as the hydraulic machines which convert hydraulic
energy 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 convened into electrical energy.
The electric power which is obtained from the hydraulic energy (energy of
water) is known as Hydroelectric power.

2. Water Turbines
CLASSIFICATION OF HYDRAULIC TURBINES
1.According to the type of energy at inlet :
(a)Impulse turbine, and (b) Reaction turbine.
2.According to the direction of flow through runner :
(a) Tangential flow turbine,
(c) Axial flow turbine, and
(b) Radial flow turbine,
(d) Mixed flow turbine.
3.According to the head at the inlet of turbine :
(a)High head turbine, (b) Medium head turbine, and
(c) Low head turbine.
4.According to the specific speed of the turbine :
(a)Low specific speed turbine, (b) Medium specific speed turbine, and
(c) High specific speed turbine.

3. Water Turbines
CLASSIFICATION OF HYDRAULIC TURBINES
Impulse turbine
If at the inlet of the turbine, the energy available is only kinetic energy, the
turbine is known as impulse turbine. E.g. Pelton wheel
Reaction turbine
If at the inlet of the turbine, the water possesses kinetic energy as well as
pressure energy, the turbine is known as reaction turbine. E.g. Francis
turbine, Kaplan turbine
Tangential flow turbine
If the water flows along the tangent of the runner, the turbine is known as
tangential flow turbine. E.g. Pelton wheel
Axial flow turbine
If the water flows through the runner along the direction parallel to the axis
of rotation of the runner, the turbine is called axial flow turbine. E.g.
Propeller Turbine, Kaplan turbine.

4. Water Turbines
CLASSIFICATION OF HYDRAULIC TURBINES
Radial flow turbine
If the water flows in the radial direction through the runner, the turbine is
called radial flow turbine.
Inward radial flow turbine
If the water flows from outwards to inwards, radially, the turbine is
known as Inward radial flow turbine. E.g. Francis turbine
outward radial flow turbine
If water flows radially from inwards to outwards, the turbine is known
as outward radial flow turbine. E.g. Fourneyron turbine
Mixed flow turbine
If the water flows through the runner in the radial direction but leaves in
the direction parallel to axis of rotation of the runner, the turbine is called
mixed flow turbine. E.g. Modern Francis turbine

5. Water Turbines
HYDROELECTRIC POWER PLANT

6. Water Turbines
ADVANTAGES OF HYDRAULIC TURBINES
1.Hydroelectricity is a renewable energy source.
2.Theplantissimpleinconstruction,robust
maintenance.
andrequiredlow
3.It can be put in the service instantly.
4.It can respond to changing loads without any difficulty.
5.The running charges are very small.
6.No fuels is burnt.
7.The plant is quite neat and clean.
8.Thewaterafterrunningtheturbinecanbeusedforirrigationand
other purpose.

7. Pelton Turbine
Pelton Turbine is a Tangential flow
impulse turbine in which the
pressure energy of water is converted
into kinetic energy to form high
speed water jet and this jet strikes
the wheel tangentially to make it
rotate.
It is also called as Pelton Wheel.
Parts and Their Functions of Pelton
Turbine
Different parts and their functions of
Pelton turbine are as follows.
1.Nozzle and Flow Regulating Arrangement
2.Runner and Buckets
3.Casing
4.Braking Jet

8. Pelton Turbine
Components
1.Nozzle and
Arrangement
Flow Regulating
The water from source is transferred
through penstock to which end a nozzle is
provided.
Using this nozzle the high speed water jet
can be formed.
To control the water jet from nozzle, a
movable needle spear is arranged inside the
nozzle.
The spear will move backward and forward
in axial direction. When it is moved forward
the flow will reduce or stopped and when it
is moved backward the flow will increase.

9. Pelton Turbine
Components….
2.Runner and Buckets
APeltonturbineconsistsofarunner,
which is a circular disc on the periphery of
which a number of buckets are mounted
with equal spacing between them.
The buckets mounted are either double
hemispherical or double ellipsoidal
shaped.
A dividing wall called splitter is provided
for each bucket which separates the
bucket into two equal parts.
The buckets are generally made of cast
iron or stainless steel or bronze depending
upon the head of inlet of Pelton turbine.

10. Pelton Turbine
Components…
3.Casing
The whole arrangement of
runner and buckets, inlet and
braking jets are covered by the
Casing.
Casing of Pelton turbine does
not perform any hydraulic
actions but prevents the
splashing of water while working
and also helps the water to
discharge to the tail race.

11. Pelton Turbine
Components…
4.Braking Jet
Braking jet is used to stop the running
wheel when it is not working.
This situation arises when the nozzle
inlet is closed with the help of spear
then the water jet is stopped on the
buckets.
But Due to inertia, the runner will not
stop revolving even after complete
closure of inlet nozzle.
The brake nozzle directs the jet of
water on the back of buckets to stop
the wheel.
The jet directed by brake nozzle is
called braking jet.

12. Pelton Turbine
Working
The working of Pelton turbine is as follows:
The water is transferred from the high head source through a long conduit called
Penstock.
Nozzle arrangement at the end of penstock helps the water to accelerate and it
flows out as a high speed jet with high velocity and discharge at atmospheric
pressure.
The jet will hit the splitter of the buckets which will distribute the jet into two
halves of bucket and the wheel starts revolving.
The kinetic energy of the jet is reduced when it hits the bucket and also due to
spherical shape of buckets the directed jet will change its direction and takes U-
turn and falls into tail race.
In general, the inlet angle of jet is in between 10 to 30, after hitting the buckets
the deflected jet angle is in between 165° to 170 °.
The water collected in tail race should not submerge the Pelton wheel in any case.
To generate more power, two Pelton wheels can be arranged to a single shaft or
two water jets can be directed at a time to a single Pelton wheel.

13. Pelton Turbine
Efficiencies of Turbines
The following are the important efficiencies of a turbine.
(a)Hydraulic Efficiency (ηh )
(b)Mechanical Efficiency (ηm )
(c)Overall Efficiency (ηo )

14. Pelton Turbine
(a) Hydraulic Efficiency
It is defined as the ratio of power given by water to the runner of a turbine (runne
is a rotating part of a turbine and on the runner vanes are fixed) to the powe
supplied by the water at the inlet of the turbine.
The power at the inlet of the turbine is more and this power goes on decreasing a
the water flows over the vanes of the turbine due to hydraulic losses as the vane
are not smooth.
Hence, the power delivered to the runner of the turbine will be less than the powe
available at the inlet of the turbine.
Thus, mathematically, the hydraulic efficiency of a turbine is written as
Hydraulic efficiency, ηh
=
Power delivered to runner
=
R.P
Power supplied at inlet
W.
P
ηh =
w1 w22(v+ v) x u
v
1
???

15. Pelton Turbine
Efficiencies of Turbines
Mechanical efficiency
Thepower delivered by water to the runner of a turbineis transmitted to the
shaft of the turbine.
Due to mechanical losses, the power available at the shaft of the turbine is less
than the power delivered to the runner of a turbine.
Theratio of thepower availableat theshaftof theturbine(known as S.P. or
B.P. ) to the power delivered to the runner is defined as mechanical efficiency.
Hence, mathematically, it is written as
Mechanical efficiency
ηm
=
Power at the shaft of the turbine
Power delivered by water to the runner
=
S.P
R.P
ηm
1w1+vw2
=
ρav(v
S.P
) x u

16. Pelton Turbine
Efficiencies of Turbines
Overall efficiency
Itisdefinedastheratioofpoweravailableattheshaftoftheturbinetothe
power supplied by the water at the inlet of the turbine.
Overall efficiency =
Power at the shaft of the turbine
Power supplied at inlet
ηo
=
S.P
W.P
=
S.P
x
R.P
W.PR.P
=
S.P
x
R.P
R.PW.P
= ηm x ηh
ηo
=
S.P
ρ?????????

17. Pelton Turbine
Problems:
A Pelton wheel is required to develop 6615 kW when working under a head of
300 m. The wheel may rotate at 500 rpm. Assuming the jet ratio as 10 and the
overall efficiency of 85%, calculate (i) Quantity of water required
Take coefficient of velocity Cv = 0.97 October-2019 (8 marks)
Solution:
Given:
Shaft power, P
Head, h
Wheel speed, N
Overall efficiency, η0
Co-efficient of velocity, Cv
= 6615kW = 6615 x 10
3 W
= 300m
= 500 rpm
= 85%= 0.85
= 0.97

18. Pelton Turbine
Quantity of water (Q)
Overall efficiency, η0=
S.P
W.P
=
S.P
ρ??????
ℎ
0.85=
Q =
6615 x 10
3
or
1000 x 9.81 x Q x 300
6615 x 10
3
0.85 x 1000 x 9.81 x 300
= 2.644 m
3/s Ans

19. Pelton Turbine
4. A double jet Pelton wheel turbine operates under a head of 100m and develops
150 kW at an overall efficiency of 90% and coefficient of velocity of 0.98.
April-2020 (7 marks)
= 2
= 100m
= 150kW = 150 x 10
3 W
= 90% = 0.90
= 0.98
Find the discharge
Solution:
Given:
No. of jets
Head, h
Power developed, P
Overall efficiency, η0
Co-efficient of velocity, Cv
To be found:
1.Discharge
we have η0
Q
=
ρ
P
??????
ℎ
=
η
P
0 ρ???ℎ

20. Pelton Turbine
Q =
η
P
0 ρ???ℎ
=
150 x 10
3
0.9 x 1000 x 9.81 x 100
= 0.16989 m
3/s
Discharge (q)
Discharge through nozzle, q
=
???
???
=
0.16989
2
= 0.085 m
3/s Ans.

21. Pelton Turbine
A Pelton wheel develops 2000 kW under a head of 100 metres and with an
overall efficiency of 85 %. Find the diameter of the nozzle, if the coefficient of
velocity of nozzle is 0.98. April-2019 (7 marks)
Two jets strikes the buckets of a Pelton wheel which is having shaft power as
15450 kW. The diameter of each jet is given as 200mm. If the net head on the
turbine is 400m, find the overall efficiency of the turbine, Take Cv =0.97
A Pelton wheel develops 3.75MW power at an effective head of 200m. If the
discharge through the nozzle is 2000 lps, calculate the overall efficiency of the
turbine

22. Reaction turbines
In reaction turbine, a part of the head (H) acting on the turbine is
converted into kinetic energy and the rest remains as pressure head.
The water first enters a set of movable blades (guide vanes) and passes
over a set of fixed runner blades.
As the water flows through the stationary parts of the turbine, whole of its
pressure energy is not transformed to kinetic energy and when the water
flows through the moving parts, there is a change both in pressure and in
the direction and velocity of flow of water.
As the water gives up its energy to the runner, both its pressure and
absolute velocity get reduced.
The water which acts on the runner blades is under a pressure above
atmospheric and the runner passages are always completely filled with
water.
There exists a difference of pressure between these two sets of blades
which is called ‘reaction pressure’ and is responsible for the motion of the
runner blades

23. Francis turbine
Main components of a Radial Flow Reaction Turbine.
The main parts of a radial flow reaction turbine are:
1.Spiral or Scroll Casing,
2.Guide mechanism,
3.Runner and runner blades
4.Draft-tube.

24. Francis turbine (Radial flow reaction turbines)

25. Francis turbine
Main components
1. Spiral or Scroll Casing.
Asmentionedabovethatincaseofreaction
turbine,casingandrunnerarealwaysfullof
water.
The water from the penstocks enters the casing
which is of spiral shape in which area of cross-
section of the casing goes on decreasing gradually.
The casing completely surrounds the runner of
the turbine. The casing is made of spiral shape, so
that the water may enter the runner at constant
velocity throughout the circumference of the
runner.
The casing is made of concrete, cast steel or plate
steel.

26. Francis turbine
Main components
2. Guide Mechanism.
It consists of a stationary circular wheel
all round the runner of the turbine. The
stationary guide vanes are fixed on the
guide mechanism.
The guide vanes allow the water to strike
the vanes fixed on the runner without
shock at inlet.
Also by a suitable arrangement, the width
between two adjacent vanes of guide
mechanism can be altered so that the
amount of water striking the runner can
be varied.

27. Francis turbine
Main components
3. Runner and runner blades
It is a circular wheel on which a series of
radial curved vanes are fixed. The surface
of the vanes are made very smooth.
The radial curved vanes are so shaped
that the water enters and leaves the
runner without shock.
The runners are made of cast steel, cast
iron or stainless steel. They are keyed to
the shaft.
The number of runner blades usually
varies between16 to 24.

28. Francis turbine
Main components
4. Draft-tube.
The pressure at the exit of the runner of a
reaction turbine is generally less than
atmospheric pressure.
The water at exit cannot be directly
discharged to the tail race. A tube or pipe
of gradually increasing area is used for
discharging water from the exit of the
turbine to the tail race.
This tube of increasing area is called draft
tube.

29. Difference between Impulse and Reaction Turbine
Sl No Impulse Turbine Reaction Turbine
1 Only kinetic energy is used to rotate the turbine. Both kinetic and pressure energy is used to rotate the
turbine.
2 Water flow through the nozzle and strike the buckets of
turbine.
Water is guided by the guide blades to flow over the
turbine.
3 All pressure energy of water converted into kinetic
energy before striking the buckets.
There is no change in pressure energy of water before
striking.
4 The pressure of the water remains unchanged and is
equal to atmospheric pressure during process.
The pressure of water is reducing after passing through
vanes.
5 Water may admitted over a part of circumference or
over the whole circumference of the wheel of turbine.
Water may admitted over a part of circumference or
over the whole circumference of the wheel of turbine.
6 In impulse turbine casing has no hydraulic
function to perform because the jet is at atmospheric
pressure. This casing serves only to prevent splashing of
water.
Casing is absolutely necessary because the pressure at
inlet of the turbine is much higher than the pressure at
outlet. It is sealed from atmospheric pressure.
7 This turbine is most suitable for large head and lower
flow rate. Pelton wheel is the example of this turbine.
This turbine is best suited for higher flow rate and
lower head situation.

30. Francis turbine
Efficiency of a Francis turbine…
5. Overall efficiency of Francis turbine
=
Shaft power
=
S P
Water PowerW P
ηo
=
P
ρgQH

31. Kaplan turbine
Kaplan Reaction turbines are axial flow
turbines in which the flow is parallel to the
axis of the shaft.
They are low head, high discharge turbine.
Kaplan turbine is a propeller type water
turbine along with the adjustable blades.
Mainly it is designed for low head water
applications.
In this water turn at right angles between the
guide vanes, runner & then flow parallel to
the shaft. It is inward flow reaction turbine.
The flow is along the radius from periphery to
the centre of the runner. (From outer dia to
the inner dia of runner).
It is capable of giving high efficiency at
overloads (up to 15-20%), at normal loads
(up to 94%).

32. Kaplan turbine
The runner of this turbine is in the form of
boss or hub which extends in a bigger dia.
Casing with proper adjustment of blades
during running.
The blade angles should be properly adjusted
so that water enters & flow through the
runner blades without shock.

33. Kaplan turbine
Components:
1.Spiral or Scroll casing:-
o Incaseofreactionturbinecasing
and runner are always full of water.
oThe water from the penstock enters
the casing which is of spiral shape
in which area of cross-section of the
casing goes on decreasing
gradually.
oThe casing completely surrounds
the runner of the turbine.
oThe casing is made of spiral shape,
so that the water may enter the
runner at constant velocity
throughout the circumference of the
runner.

34. Kaplan turbine
2. Guide Mechanism:-
o Itconsistsofastationarycircularwheelall-
round the runner of the turbine.
oThestationaryguidevanesarefixedonthe
guide mechanism.
oTheguidevanesallowthewatertostrikethe
vanes fixed on the runner without shock at inlet.
oAlsobyasuitablearrangement,the
betweentwoadjacentvanesofa
width
guide
mechanism can be altered so that the amount of
water striking the runner can be varied.

35. Kaplan turbine
3.Runner:-
It is a circular wheel, also called ‘hub’ or ‘boss’
on which a series of radial curved vanes are
fixed.
The surface of the vanes is made very smooth.
The radial curved vanes are so shaped that
water enters and leaves the runner without
shock.
The runners are made of cast steel, cast iron or
stainless steel.
In Kaplan turbine, the shaft is the extended
part of runner with smaller diameter.
4.Runner Vanes:
This is an important part of this turbine. The
blades are attached to the runner.
From the runner, the shaft is attached and
connected with the generator. When the runner
rotates, the shaft also rotates.

36. Kaplan turbine
5.Draft tube:-
The pressure at the exit of an axial
turbine is generally less than atmospheric
pressure.
The water at exit cannot be directly
discharged to the tail race.
A tube or pipe of a gradually increasing
area is used for discharging water from
the exit of the turbine to the tail race. This
tube of increasing area is called draft
tube.
Types of draft tubes:
1.Straight conical draft tube
2.Hydracone or Moody’s Spreading tube
3.Simple Elbow draft tube
4.Elbow tube have circular cross section
at inlet & rectangular at outlet

37. Kaplan turbine
1.Straight conical draft tube
The shape of the tube resembles that of a frustum of a
cone.
The cone angle varies from 4
0 to 8
0
The efficiency of the conical tube is about 85% to 90 %
2.Hydracone or Moody’s Spreading tube
This is the modification of conical tube and a solid
conical cone is provided in the centre of the tube with a
flare at the bottom end.
Such an arrangement allows large exit area without
excessive length.
The solid core at the centre enable full flow and
hydracone spreading draft tube reduces the eddy
losses.
The efficiency of the tube is about 85%

38. Kaplan turbine
3.Simple Elbow draft tube
This type is used for the low head.
TheEfficiencyofthistubeisabout60percent
which is moderate.
The area of inlet and outlet are the same.
A little bit the outlet section is changed.
4.Elbow tube have circular cross section at inlet &
rectangular at outlet
The cross section of this type of tube change
from circular section at the vertical leg to the
rectangular section at the horizontal leg takes
place in the bend.
Efficiency about 85%

39. Specific speed of a turbine
The specific speed of a turbine is defined as the speed of a turbine which is
identical in shape, geometrical dimensions, blade angles, gate opening, etc.
which would develop unit power when working under a unit head.
Mathematically,
Specific speed, Ns =
??????
/
???
5 4
Sl No Specific speed Type of turbine
1 8.5 to 30 Pelton wheel with single jet
2 30 to 50 Pelton wheel with two or more jet
3 50 to 225 Francis turbine
4 225 to 860 Kaplan turbine

40. Specific speed of a turbine
A turbineistooperateundera headof25m at 200 .RPM.The dischargeis
9m
3/s. If the overall efficiency is 90%, determine
(i)power generated
(ii)specific speed of the turbine
(iii)type of turbine
Solution
Net head, h
Speed of tuebine, N
Overall efficiency, ηo
Discharge, Q
Power generated, P
= 25 m
= 200 ?????????
= 90% = 0.80
= 9m
3/s
= ?
Specific speed of the turbine, Ns = ?
Type of turbine ?

41. Specific speed of a turbine
We have
Overall efficiency, ηo
Or Power generated, P
=
P
ρgQh
=ηoρgQh
=0.9 x 1000 x 9.81 x 9 x 25
= 1986525 W
= 198.6525 kW Ans
Specific speed, Ns =
200198.6525
/
25
5 4
= 50.42 Ans
As the specific speed 50.42 lies between 50-225 and hence the
type of turbine is Francis turbine Ans

42. Unit quantities of turbines
A turbine operates most efficient at its design point, at a particular
combination of head, discharge ,speed and power output, but in actual
practice hardly any turbine operates at its designed parameters.
In order to predict the behaviour of a turbine working under varying
conditions of head, speed, and power, recourse has been made to the
concept of unit.
The unit quantities give the speed, discharge and power for a particular
turbine under a head of 1m assuming the same efficiency.
The following are the three important unit quantities.
1.Unit speed
2.Unit power
3.Unit discharge

43. Unit quantities of turbines
1.Unit speed (Nu)
Thespeedoftheturbine,workingunderunit head(say1m)isknownas
unit speed of the turbine
N = NuH
or
u
N=
N
H
u
N=
N
H
2.Unit discharge (Qu)
The discharge of the turbine working under a unit head (say 1 m) is known
as unit discharge.
or
u
Q=
Q
H
u
Q=
Q
H

44. Unit quantities of turbines
3.Unit Power (Pu)
The power developed by a turbine, working under a unit head (say 1 m) is
known as unit power of the turbine.
u
P = PH
3/2
or P=
P
u H3/2
u
P=
P
H
3/2

45. Selection of turbines based on specific speed
and head
Sl
No
Type of turbine Head (m)Specific
speed
Max.
hydraulic
efficiency
1
Peltonturbine with one jetUpto 200012-30
90
Peltonturbine with two jetsUpto 150017-50
Peltonturbine with four jetsUpto 500 24-70
2Francis turbine 30- 300 80-400 93
3Kaplan turbine 3-10 300-1000 91