1. Prof. S. M. Harle Dept of Civil Engg PRMCEAM
Turbines
Prof. S. M. Harle
Dept of Civil Engg
PRMCEAM

2. Intoduction Water under pressure contains energy.
Turbines convert the energy in water into rotating mechanical energy.
Impulse turbines convert the kinetic energy of a jet of water to mechanical energy.
Reaction turbines convert potential energy in pressurized water to mechanical energy.

3. The device which converts hydraulic energy into mechanical energy or vice versa is known as Hydraulic Machines.
The hydraulic machines which convert hydraulic energy into mechanical energy are known as Turbines and that convert mechanical energy into hydraulic energy is known as Pumps.

4. General layout of Hydraulic Plant

6. A Dam constructed across a river or a channel to store water
A Dam constructed across a river or a channel to store water. The reservoir is also known as Headrace.
Pipes of large diameter called Penstocks which carry water under pressure from storage reservoir to the turbines. These pipes are usually made of steel or reinforced concrete.
Turbines having different types of vanes or buckets or blades mounted on a wheel called runner.
Tailrace which is a channel carrying water away from the turbine after the water has worked on the turbines. The water surface in the tailrace is also referred to as tailrace.

7. Important Terms:
Gross Head (Hg ): It is the vertical difference between headrace and tailrace.
Net Head:(H): Net head or effective head is the actual head available at the inlet of the to work on the turbine.
H = Hg – hL
Where hL is the total head loss during the transit of water from the headrace to tailrace which is mainly head loss due to friction, and is given by

8. Where f is the coefficient of friction of penstock depending on the type of material of penstock
L is the total length of penstock
V is the mean flow velocity of water through the penstock
D is the diameter of penstock and
g is the acceleration due to gravity

9. A hydraulic machine is a device in which mechanical energy is transferred from the liquid flowing through the machine to its operating member (runner, piston and others) or from the operating member of the machine to the liquid flowing through it.
Hydraulic machines in which, the operating member receives energy from the liquid flowing through it and the inlet energy of the liquid is greater than the outlet energy of the liquid are referred as hydraulic turbines.

10. Hydraulic machines in which energy is transmitted from the working member to the flowing liquid and the energy of the liquid at the outlet of the hydraulic machine is less than the outlet energy are referred to as pumps.
It is well known from Newton’s Law that to change momentum of fluid, a force is required. Similarly, when momentum of fluid is changed, a force is generated. This principle is made use in hydraulic turbine.

11. In a turbine, blades or buckets are provided on a wheel and directed against water to alter the momentum of water. As the momentum is changed with the water passing through the wheel, the resulting force turns the shaft of the wheel performing work and generating power.
A hydraulic turbine uses potential energy and kinetic energy of water and converts it into usable mechanical energy. The mechanical energy made available at the turbine shaft is used to run an electric power generator which is directly coupled to the turbine shaft

12. The electric power which is obtained from the hydraulic energy is known as Hydroelectric energy. Hydraulic turbines belong to the category of roto- dynamic machinery.
The hydraulic turbines are classified according to type of energy available at the inlet of turbine, direction of flow through vanes, head at the inlet of the turbines and specific speed of the turbines.

13. According to the type of energy at inlet:
Impulse turbine:
In the impulse turbine, the total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle. That is the entire available energy of the water is converted in to kinetic energy.
Although there are various types of impulse turbine designs, perhaps the easiest to understand is the Pelton wheel turbine. It is most efficient when operated with a large head and lower flow rate.

14. Reaction turbine
Reaction turbines on the other hand, are best suited -for higher flow rate and lower head situations.
In this type of turbines, the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades; therefore, it is called as reaction turbine.
For, a reaction turbine, the penstock pipe feeds water to a row of fixed blades through casing.

15. These fixed blades convert a part of the pressure energy into kinetic energy before water enters the runner.
The water entering the runner of a reaction turbine has both pressure energy and kinetic energy.
Water leaving the turbine is still left with some energy (pressure energy and kinetic energy).
Since, the flow from the inlet to tail race is under pressure, casing is absolutely necessary to enclose the turbine.
In general, Reaction turbines are medium to low-head, and high- flow rate devices.
The reaction turbines in use are Francis and Kaplan

16. According to the direction of flow through runner:
Tangential flow turbines:
In this type of turbines, the water strikes the runner in the direction of tangent to the wheel. Example: Pelton wheel turbine.
Radial flow turbines:
In this type of turbines, the water strikes in the radial direction. accordingly, it is further classified as,
Inward flow turbine: The flow is inward from periphery to the centre (centripetal type). Example: old Francis turbine.

17. Outward flow turbine: The flow is outward from the centre to periphery (centrifugal type). Example: Fourneyron turbine.
Axial flow turbine:
The flow of water is in the direction parallel to the axis of the shaft. Example: Kaplan turbine and propeller turbine.
Mixed flow turbine:
The water enters the runner in the radial direction and leaves in axial direction. Example: Modern Francis turbine.

18. According to the head at inlet of turbine:
High head turbine:
In this type of turbines, the net head varies from 150m to 2000m or even more, and these turbines require a small quantity of water. Example: Pelton wheel turbine.
Medium head turbine:
The net head varies from 30m to 150m, and also these turbines require moderate quantity of water. Example: Francis turbine.
Low head turbine:
The net head is less than 30m and also these turbines require large quantity of water. Example: Kaplan turbine.

19. According to the specific speed of the turbine
The specific speed of a turbine is defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head). It is prescribed by the relation
Low specific speed turbine:
The specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet ) Example: Pelton wheel turbine.
Medium specific turbine: The specific speed is varies from 50 to Example: Francis turbine.
High specific turbine: the specific speed is more than Example: Kaplan turbine.

20. Classification of Turbines
The hydraulic turbines can be classified based on type of energy at the inlet, direction of flow through the vanes, head available at the inlet, discharge through the vanes and specific speed.

21. Turbine
Type of Energy
Head
Discharge
Direction of flow
Specific Speed
Name
Type
Pelton wheel
Impulse
Kinetic
High Head >250m to 1000m
Low
Tangential to runner
Low < 35 single jet multiple jet
Francis Turbine
Reaction Turbine
Kinetic + Pressure
Medium 60m to 150m
Medium
Radial Flow
Medium 60 to 300
Mixed Flow
Kaplan Turbine
Low <30m
High
Axial Flow
High 300 to 1000

22. Radial flow turbines
Radical flow turbines are those turbines in which the water flows in radial direction. The water may flow radically from outwards to inwards or from inwards to outwards.
If the water flows from outwards to inwards through the runner, the turbine is known as inward radial flow turbine. If the water flows from inwards to outwards, the turbine is known as outward radial flow turbine.
Reaction turbine means that the water at inlet of turbine possesses kinetic energy as well as pressure energy.

23. The main parts of a radial flow reaction turbine are:
Casing: - The water from penstocks enters the casing which is of spiral shape in which area of cross section of casing goes on decreasing gradually. The casing completely surrounds the runner of the turbine.
Guide mechanism: - It consists of stationary circular wheel all round the runner of the turbine. The stationary guide vanes are fixed on guide mechanism. The guide vanes allow the water to strike the vanes fixed on the runner without shock at inlet.

24. Runner: - It is a circular wheel on which a series of radial curved vanes are fixed. The surfaces of the vanes are made very smooth. The radial curved are so shaped that the water enters and leaves without shock.
Draft tube: - The pressure at the exit of the runner of reaction turbine is generally less than atmospheric pressure. The water 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 turbine to the tailrace. This tube of increasing area is called draft tube.

25. Axial flow turbines
If the water flows parallel to the axis of the rotation of the shaft, the turbine is known as axial flow turbine.
If the head at the inlet of the turbine is the sum of pressure energy and kinetic energy and during the flow of water through runner a part of pressure energy is converted into kinetic energy, the turbine is known as reaction turbine.
For the axial flow reaction turbines, the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as hub. The vanes are fixed on the hub and hence hub acts as runner for axial flow reaction turbine.

26. The following are the important type of axial flow turbines:
Propeller turbine
Kaplan turbine
When the vanes are fixed to the hub and they are not adjustable, the turbine is known as propeller turbine.
If vanes on hub are adjustable the turbine is known as a Kaplan turbine. This turbine is suitable where a large quantity of water at low heads is available.

27. Difference between Impulse and Reaction turbine
Impulse turbine
Reaction turbine
The entire available energy of the water is
converted into kinetic energy.
Only a portion of the fluid energy is converted
into kinetic energy before the fluid enters the
turbine runner.
The work is done only by the change in the
kinetic energy of the jet.
The work is done partly by the change in the
velocity head, but almost entirely by the
change in pressure head.
Flow regulation is possible without loss.
It is not possible to regulate the flow without
loss.
Unit is installed above the tailrace.
Unit is entirely submerged in water below the
tailrace.
Casing has no hydraulic function to perform,
because the jet is unconfined and is at
atmospheric pressure. Thus, casing serves only
to prevent splashing of water.
Casing is absolutely necessary, because the
pressure at inlet to the turbine is much higher
than the pressure at outlet. Unit has to be
sealed from atmospheric pressure.
It is not essential that the wheel should run full
and air has free access to the buckets.
Water completely fills the vane passage.

28. PELTON WHEEL OR TURBINE
Pelton wheel, named after an eminent engineer, is an impulse turbine wherein the flow is tangential to the runner and the available energy at the entrance is completely kinetic energy.
Further, it is preferred at a very high head and low discharges with low specific speeds.
The pressure available at the inlet and the outlet is atmospheric.

30. The main components of a Pelton turbine are:
Nozzle and flow regulating arrangement :
Water is brought to the hydroelectric plant site through large penstocks at the end of which there will be a nozzle, which converts the pressure energy completely into kinetic energy.
This will convert the liquid flow into a high-speed jet, which strikes the buckets or vanes mounted on the runner, which in-turn rotates the runner of the turbine.
The amount of water striking the vanes is controlled by the forward and backward motion of the spear.

32. As the water is flowing in the annular area between the annular area between the nozzle opening and the spear, the flow gets reduced as the spear moves forward and vice-versa.
Runner with buckets:
Runner is a circular disk mounted on a shaft on the periphery of which a number of buckets are fixed equally spaced as shown in Fig.
The buckets are made of cast -iron cast -steel, bronze or stainless steel depending upon the head at the inlet of the turbine.
The water jet strikes the bucket on the splitter of the bucket and gets deflected through (α) °.

34. Casing:
It is made of cast -iron or fabricated steel plates.
The main function of the casing is to prevent splashing of water and to discharge the water into tailrace.
Breaking jet:
Even after the amount of water striking the buckets is completely stopped, the runner goes on rotating for a very long time due to inertia.
To stop the runner in a short time, a small nozzle is provided which directs the jet of water on the back of bucket with which the rotation of the runner is reversed.
This jet is called as breaking jet.

36. PeltonTurbines

39. Francis Turbine

40. The main parts are:
Penstock: It is a large size conduit which conveys water from the upstream to the dam/reservoir to the turbine runner.
Spiral Casing: It constitutes a closed passage whose cross- sectional area gradually decreases along the flow direction; area is maximum at inlet and nearly zero at exit.
Guide Vanes: These vanes direct the water on to the runner at an angle appropriate to the design, the motion of them is given by means of hand wheel or by a governor.

41. Governing Mechanism: It changes the position of the guide blades/vanes to affect a variation in water flow rate, when the load conditions on the turbine change.
Runner and Runner Blades: The driving force on the runner is both due to impulse and reaction effect. The number of runner blades usually varies between 16 to 24.
Draft Tube: It is gradually expanding tube which discharges water, passing through the runner to the tail race.

42. Working:
Francis turbine has a purely radiate flow runner. Water under pressure, enters the runner from the guide vanes towards the center in radial direction and discharges out of the runner axially.
Francis turbine operates under medium heads. Water is brought down to the turbine through a penstock and directed to a number of stationary orifices fixed all around the circumference of the runner.
These stationary orifices are called as guide vanes. The head acting on the turbine is transformed into kinetic energy and pressure head.

43. Due to the difference of pressure between guide vanes and the runner (called reaction pressure), the motion of runner occurs. That is why a Francis turbine is also known as reaction turbine.
The pressure at inlet is more than that at outlet. In Francis turbine runner is always full of water. The moment of runner is affected by the change of both the potential and kinetic energies of water.
After doing the work the water is discharged to the tail race through a closed tube called draft tube.

44. Draft Tubes:
In radial flow turbines, as the water flows from higher pressure to lower pressure, it cannot come out of the turbine and hence a divergent tube is connected to the end of the turbine.
This divergent tube, one end of which is connected to the outlet of the turbine and the other is immersed well below the tail race.

45. Functions of Draft tube:
It is to increase the pressure from inlet to outlet of the draft tube as it flows through it and hence increase it more than atmospheric pressure.
To safely discharge the water that has worked on the turbine to the tail race.