2. HYDRAULIC TURBINE
Definition:
The machine/device which converts hydraulic
energy into mechanical energy is called as hydraulic
turbine.
Examples:
1) Pelton Wheel Turbine
2) Francis Turbine
3) Kaplan Turbine
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Prof. V. R. Muttagi
3. Prof. V. R. Muttagi 3
Classification of Hydraulic Turbine
1) According to Energy at Inlet:
a) Impulse Turbine: Kinetic Energy is Maximum than Pressure Energy.
e.g. Pelton Wheel Turbine
b) Reaction Turbine: Pressure Energy is Maximum than Kinetic Energy.
e.g. Francis Turbine and Kaplan Turbine
2) According to Direction of Flow Through Runner:
a) Tangential Flow: Water flows along the tangent of runner.
e.g. Pelton Wheel Turbine
b) Radial Flow: Water flows along the radius through runner.
c) Axial Flow: Water flows along the axis of rotation of runner.
d) Mixes Flow: Water inlet radial direction and exit in axial direction.
4. Prof. V. R. Muttagi 4
Classification of Hydraulic Turbine
3) According to HeadAvailable at Inlet:
a) Low Head: Head < 60 meters
e.g. Kaplan Turbine
b) Medium Head: 60 meters < Head < 250 meters
e.g. Francis Turbine
c) High Head: 250 meters < Head
e.g. Pelton Wheel Turbine
4) According to Specific Speed of Turbine:
a) Low Specific Speed: Specific Speed < 60
e.g. Pelton Wheel Turbine
b) Medium Specific Speed: 60 < Specific Speed < 300
e.g. Francis Turbine
c) High Specific Speed: 300 < Specific Speed
e.g. Kaplan Turbine
6. Prof. V. R. Muttagi 6
Hydro-Electric Power Plant
1) Dam:
Awall constructed across the flow of river.
2) Penstock:
Apipe which convey the water from dam to turbine
house.
3) Turbine House:
Assembly of runner, shaft to convert hydro energy into
mechanical energy.
4) Surge Tank:
Astorage tank fitted on penstock before valve to avoid
water hammer.
5) Valve House:
To control the rate of flow of water through penstock.
7. DEFINITIONS OF HEADS
1) GROSS HEAD :Gross head is basically defined as the difference
between the head race level and tail race level when water is not
flowing. Gross head will be indicated by Hg as displayed here in
following figure.
2) NET HEAD
Net head is basically defined as the head available at the inlet of
the turbine. Net head is also simply called as effective head.
Net head, H = Gross head (Hg) – head loss due to friction (hf)
8. Efficiencies of a turbine
There are following important efficiencies that we will
discuss here in this post.
1) Hydraulic efficiency
2) Mechanical Efficiency
3) Volumetric efficiency
4) Overall Efficiency
1) Hydraulic efficiency : Hydraulic efficiency is basically defined as the ratio
of power given by water to the runner of turbine to the power supplied by the
water at the inlet of the turbine. Hydraulic efficiency will be indicated by ηh
Hydraulic efficiency of a turbine could be written as mentioned here
Hydraulic efficiency (ηh) = Power delivered to the runner of turbine / Power
supplied at the inlet of turbine
Hydraulic efficiency (ηh) = R.P/ W.P
R.P = Power delivered to the runner of turbine
W.P = Power supplied at the inlet of turbine or water power
9. 2)Mechanical Efficiency
Mechanical efficiency is basically defined as the ratio of
power available at the shaft of the turbine to the power
delivered to the runner of the turbine. Mechanical
efficiency will be indicated by ηm.
Mechanical efficiency of a turbine could be written as
mentioned here
Mechanical efficiency (ηm) = Power available at the
shaft of the turbine / Power delivered to the runner of
the turbine
Mechanical efficiency (ηm) = S.P/ R.P
10. 3)Volumetric Efficiency
The volume of the water striking the runner of a turbine
will be slightly less than the volume of the water
supplied to the turbine as some amount of water will be
discharged to the tail race without striking the runner of
the turbine
Volumetric efficiency of a turbine could be written as
mentioned here
Volumetric efficiency (ηv) = Volume of the water
actually striking the runner of the turbine / Volume of
water supplied to the turbine
11. 4)Overall Efficiency
Overall efficiency is basically defined as the ratio of the
power available at the shaft of the turbine to the power
supplied by the water at the inlet of the turbine. Overall
efficiency will be indicated by ηo
Overall efficiency, ηo = Power available at the shaft of
the turbine / Power supplied by the water at the inlet of
the turbine
Overall efficiency, ηo = S.P/W.P
Overall efficiency is also defined as the product of
mechanical efficiency and hydraulic efficiency
Overall efficiency = Mechanical efficiency x Hydraulic
efficiency
ηo = ηm x ηh
12. Pelton Wheel Turbine – Main Parts&Construction
Prof. V. R. Muttagi 12
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 Whee
13. Workingof PeltonTrubine
1.The water stored at a high head is made to flow through
the penstock and reaches the nozzle of the Pelton turbine.
2.The nozzle increases the K.E. of the water and directs the
water in the form of a jet.
3.The jet of water from the nozzle strikes the buckets
(vanes) of the runner. This made the runner rotate at a very
high speed.
4.The quantity of water striking the vanes or buckets is
controlled by the spear present inside the nozzle.
5. The generator is attached to the shaft of the runner
which converts the mechanical energy ( i.e. rotational
energy) of the runner into electrical energy.
14. Pelton Wheel Turbine – Main Components
1) Nozzle:
a) It is fixed on end of penstock.
b) Area of nozzle is gradually decreasing.
c)Convert pressure energy of water into kinetic
energy.
2) Spear and Spear RodAssembly:
a) Spear is at opening end of nozzle.
b) Spear connected to spear rod and hand wheel.
c) Regulate the discharge through nozzle according to load on turbine.
3) Runner or Wheel:
a) It is a circular disc keyed with the shaft.
b) To transmits the power to shaft.
Prof. V. R. Muttagi 14
15. Pelton Wheel Turbine – Main Components
4) Buckets:
a) Hemispherical in shape.
b) Fixed on the circumference of the runner or wheel.
Where,
d = Diameter of jet
L = Length or height of bowl = 2d to 3d
B = Width of bucket = 3d to 4d
T = Depth of bucket = 0.27B to 0.32B
M = Notch width = 1.1d to 1.2d
Prof. V. R. Muttagi 15
16. Pelton Wheel Turbine – Main Components
5) Breaking Jet:
a) Applied in opposite direction to rotation of wheel.
b)Resistance to rotation of wheel due to inertia forces
while to stop wheel.
6) Deflector:
a) Fixed below the nozzle.
b) Deflects the direction of jet while to stop wheel.
c) No hydraulic function.
7) Casing:
a) Avoid splashing of water over runner.
b) No hydraulic function.
Prof. V. R. Muttagi 16
17. Pelton Wheel Turbine – Work Done & Efficiency
Velocity Triangle
1) Low Speed Turbine
Inlet Velocity Triangle
Outlet Velocity Triangle
Prof. V. R. Muttagi 17
18. Pelton Wheel Turbine – Work Done & Efficiency
Velocity Triangle
2) Medium Speed Turbine
Inlet Velocity Triangle
Outlet Velocity Triangle
Prof. V. R. Muttagi 18
19. Pelton Wheel Turbine – Work Done & Efficiency
Velocity Triangle
3) High Speed Turbine
Inlet Velocity Triangle
Outlet Velocity Triangle
Prof. V. R. Muttagi 19
20. Pelton Wheel Turbine – Work Done & Efficiency
1) Velocity of Jet at Inlet
2) Uniform Velocity of Bucket
Prof. V. R. Muttagi 20
21. Pelton Wheel Turbine – Work Done & Efficiency
3) Mass Flow Rate of Water
4) Force Exerted by Jet on Bucket
From inlet velocity triangle, initial velocity of jet is,
From outlet velocity triangle, final velocity of jet is,
Prof. V. R. Muttagi 21
22. Pelton Wheel Turbine – Work Done & Efficiency
Hence, force exerted by jet on bucket for all speed runner is,
5) Work Done by Jet on Runner per Second
6) Power Developed
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23. Pelton Wheel Turbine – Work Done & Efficiency
7) Hydraulic Efficiency
8) Mechanical Efficiency
Prof. V. R. Muttagi 23
24. Pelton Wheel Turbine – Work Done & Efficiency
9) Overall Efficiency
10) Specific Speed
Prof. V. R. Muttagi 24
25. Pelton Wheel Turbine – Design Aspects
1) Speed Ratio
2) Friction Factor
3) Jet Ratio
Prof. V. R. Muttagi 25
26. Pelton Wheel Turbine – Design Aspects
4) Number of Buckets
5)Angle of Deflection
The angle of deflection of jet through the bucket varies between 160°
to 170°. Take as 165°.
Prof. V. R. Muttagi 26
27. Francis Turbine – main parts& Construction
Prof. V. R. Muttagi 27
Working:
1.This is the most efficient hydraulic turbine.
2.Large Francis turbine is individually designed
for the site to operate at the highest possible
efficiency, typically over 90%.
3.Francis type units cover a wide head range,
from 20 to 700 M and their output varies from a
few kilowatts 200 megawatt.
4.In addition to electrical products and they may
also be used for pumped storage; Where is
Reservoir is filled by the turbine (acting as
a pump) during low power demand, and then
reversed and used to generate power during
peak demand.
5.Francis turbine may be designed for a wide
range of heads and flows. This, along with their
high efficiency, has made them the most widely
used turbine in the world
28. The Francis turbine is a type of water turbine. It is an inward-
flow reaction turbine that combines radial and axial flow concepts.
Francis turbines are the most common water turbine in use today, and
can achieve over 95% efficiency
29. Francis Turbine – Main Components
1) Scroll Casing
a) It is surrounding to the runner, guide
vanes and moving vanes.
b) It is always full with water.
c) Shape is spiral.
d) Reducing area is to maintain velocity of
water at constant.
2) Runner
a) It is rotary part of turbine keyed with
shaft.
b) Vanes are fixed on inlet ring and outlet
ring.
c) Water enters radially and exit axially.
Prof. V. R. Muttagi 29
30. Francis Turbine – Main Components
3) Guide Vanes
a) It is surrounding to the moving vanes.
b) Guide vanes are fixed vanes.
c) Shape is like aerofoil.
d) Guide the water from casing to runner.
4) Moving Vane
a) It is surrounding to the runner.
b) Shape is aerofoil.
c) One end is pivoted on fixed ring and
another end is pivoted on moving ring.
d) Regulating the discharge of water from
casing to runner as per desired load.
Prof. V. R. Muttagi 30
31. Francis Turbine – Main Components
5) Draft Tube
a) It is fixed at exit of turbine to tail race.
b) Convert kinetic energy of water to pressure energy.
c) Increase head on turbine.
d) Improve efficiency and reduces cavitations.
Prof. V. R. Muttagi 31
32. Francis Turbine – Work Done & Efficiency
Velocity Triangle
Prof. V. R. Muttagi 32
33. Francis Turbine – Work Done & Efficiency
1) Uniform Velocity of Inlet and Outlet Tip
2) Work Done
Work done per second per unit weight of water
Prof. V. R. Muttagi 33
34. Francis Turbine – Work Done & Efficiency
3) Discharge of Turbine
Prof. V. R. Muttagi 34
35. Francis Turbine – Work Done & Efficiency
4) Hydraulic Efficiency
5) Mechanical Efficiency
Prof. V. R. Muttagi 35
36. Francis Turbine – Work Done & Efficiency
6) Overall Efficiency
7) Speed Ratio
8) Flow Ratio
9) Ratio of Width to Diameter
Prof. V. R. Muttagi 36
38. Kaplan Turbine – Working
1) Propeller type turbine.
2) Scroll casing is surrounding to the runner, guide blades and
moving blades to maintain kinetic energy at constant.
3) Fixed guide vanes are surrounding to the runner.
4) Hub or boss of runner is keyed with the shaft of turbine.
5)The movable blades are fixed on
the circumference of hub which
may change an angle according to
load on turbine.As shown in figure.
Prof. V. R. Muttagi 38
39. A Kaplan turbine is a type of
propeller hydro turbine (specifically
a reaction turbine) used
in hydroelectric plants. Water flows
both in and out of Kaplan turbines
along its rotational axis (axial flow).
What makes Kaplan turbines special is
the blades can change their angle on
demand to maintain
maximum efficiency for different flow
rates of water.[2] Water flowing
through a Kaplan turbine loses
pressure, this means that a Kaplan
turbine is a reaction turbine (similar to
a Francis turbine)
40. Prof. V. R. Muttagi 40
Draft Tube – Definition, Function and Types
Adraft tube is a pipe of gradually increasing area which connects the
exit of runner of a turbine to tail race.
It discharges the water from runner to tail race.
Functions of Draft Tube
1) It increases the net head available on turbine.
2) To convert the kinetic energy of water at exit of runner into pressure
energy so that useful head at runner exit is increased.
3) It reduces the cavitations in reaction turbine.
Types of Draft Tube
1) Conical Draft Tube
2) Simple Elbow Draft Tube
3) Elbow Draft Tube with Circular Inlet and Rectangular Outlet
4) Moody’s Spreading Draft Tube
41. Draft Tube – Types
1) Conical Draft Tube
1) It has circular inlet and circular outlet.
2) It is a simple taper tube.
3) The taper angle varies from 4° to 7°.
4) It is fabricated by mild steel plates.
5) It has an efficiency up to 90%.
6) It is employed for vertical shaft reaction
turbines.
Prof. V. R. Muttagi 41
42. Draft Tube – Types
2) Simple Elbow Draft Tube
1) It has circular cross-section throughout
from inlet to outlet.
2) It is a simple tube with uniform section
turned into 90°.
3) It reduces depth and cost of excavation.
4) It is made of concrete with steel lining
at inlet to reduce cavitation.
5) It is having an efficiency up to 60%.
Prof. V. R. Muttagi 42
43. Draft Tube – Types
2) Elbow Draft Tube with Circular Inlet and Rectangular Outlet
1) It has circular inlet and rectangular outlet.
2) It reduces depth and cost of excavation.
3) It is made of concrete with steel lining at inlet to reduce cavitation.
4) It is having an efficiency up to 60% to 80%.
Prof. V. R. Muttagi 43
44. Draft Tube – Types
2) Moody’s Spreading Draft Tube
1) It is similar to conical draft tube.
2) Asolid central core at centre to reduce the whirling.
3) It is used for vertical shaft turbine.
4) It is having an efficiency up to 85%.
Prof. V. R. Muttagi 44
48. Draft Tube
The water after working on the turbine, imparts its energy to the vanes and
runner, there by reducing its pressure less than that of atmospheric Pressure. As
the water flows from higher pressure to lower Pressure, It can not come out of the
turbine and hence a divergent tube is Connected to the end of the turbine.
Draft tube is a divergent tube one end of which is connected to the outlet Of the
turbine and other end is immersed well below the tailrace (Water level).
The major function of the draft tube is to increase the pressure from the inlet to
outlet of the draft tube as it flows through it and hence increase it more than
atmospheric pressure. The other function is to safely Discharge the water that
has worked on the turbine to tailrace.
51. Surge Tanks
Surge tank (or surge chamber) is a device introduced within a hydropower water
conveyance system having a rather long pressure conduit to absorb the excess
pressure rise in case of a sudden valve closure. The surge tank is located
between the almost horizontal or slightly inclined conduit and steeply sloping
penstock and is designed as a chamber excavated in the mountain.
It also acts as a small storage from which water may be supplied in case of a
sudden valve opening of the turbine.
In case of a sudden opening of turbine valve, there are chances of penstock
collapse due to a negative pressure generation, if there is no surge tank.
53. Governing of Turbines
Governing means Speed Regulation.
Governing system or governor is the main controller of the hydraulic turbine. The
governor varies the water flow through the turbine to control its speed or power
output.
1. Impulse Turbine
a) Spear Regulation
b) Deflector Regulation
c) Combined
2. Reaction Turbine
55. The unit quantities give the speed, discharge and power for a particular
turbine under a head of 1m assuming the same efficiency. Unit quantities
are used to predict the performance of turbine.
1. Unit speed (Nu) - Speed of the turbine, working under unit head
2. Unit power (Pu) - Power developed by a turbine, working under a unit head
3. Unit discharge (Qu) - The discharge of the turbine working under a unit head
Performance of Turbines under unit quantities
58. Unit Quantities & Specific Speed
Problems:
1. Suggest a suitable type of turbine to develop 7000 kW power under a head
of 20m while operating at 220 rpm. What are the considerations for your
suggestion.
2. A turbine is to operate under a head of 25m at 200 rpm. The discharge is 9
m3/s. If the efficiency is 90%, determine:
i) Power generated ii) Speed and Power at a head of 20m
59. Characteristics Curves of Turbine
These are curves which are characteristic of a particular turbine which helps in
studying the performance of the turbine under various conditions. These
curves pertaining to any turbine are supplied by its manufacturers based on actual
tests.
The characteristic curves obtained are the following:
a) Constant head curves or main characteristic curves
b) Constant speed curves or operating characteristic curves
c) Constant efficiency curves or Muschel curves
60. Constant head curves or main characteristic curves
Constant head curves:
Maintaining a constant head, the speed of the turbine is varied by admitting different
rates of flow by adjusting the percentage of gate opening. The power P developed is
measured mechanically. From each test the unit power Pu, the unit speed Nu, the
unit discharge Qu and the overall efficiency are determined.
The characteristic curves drawn are
a) Unit discharge vs unit speed
b) Unit power vs unit speed
c) Overall efficiency vs unit speed
61.
62. Constant speed curves or operating characteristic curves
Constant speed curves:
In this case tests are conducted at a constant speed varying the head H and
suitably adjusting the discharge Q. The power developed P is measured
mechanically. The overall efficiency is aimed at its maximum value.
The curves drawn are
63.
64. Constant efficiency curves or Muschel curves
Constant efficiency curves:
These curves are plotted from data which can be obtained from the constant
head and constant speed curves. The object of obtaining this curve is to determine
the zone of constant efficiency so that we can always run the turbine with
maximum efficiency.
This curve also gives a good idea about the performance of the turbine at
various efficiencies.
67. Similitude of Turbines - Problems
Problems:
1. A hydraulic turbine develops 120 KW under a head of 10 m at a speed of
1200 rpm and gives an efficiency of 92%. Find the water consumption and
the specific speed. If a model of scale 1: 30 is constructed to operate under a
head of 8m what must be its speed, power and water consumption to run
under the conditions similar to prototype.
2. A model turbine 1m in diameter acting under a head of 2m runs at 150 rpm.
Estimate the scale ratio if the prototype develops 20 KW under a head of 225
m with a specific speed of 100.
68. Cavitations
If the pressure of a liquid in course of its flow becomes equal to its vapour pressure
at the existing temperature, then the liquid starts boiling and the pockets of vapour
are formed which create vapour locks to the flow and the flow is stopped. The
phenomenon is known as cavitation.
To avoid cavitation, the minimum pressure in the passage of a liquid flow, should
always be more than the vapour pressure of the liquid at the working temperature.
In a reaction turbine, the point of minimum pressure is usually at the outlet end of
the runner blades, i.e., at the inlet to the draft tube.
