jntuh R18 B.TECH HHM UNIT-4

1. MOODNARESH, M.Tech-JNTUH,(Ph.D-JNTUH)
Asst.prof
PETW

13. Pelton Wheel Turbine
• The Pelton wheel turbine is a tangential flow
impulse turbine used for high heads of water and
It is invented by Lester Allan Pelton, an American
Engineer.
• the energy available at the inlet of the turbine is
only kinetic energy. The pressure energy at the
inlet and outlet of the turbine is atmospheric.
• This is a hydraulic turbine and the main uses of
these turbines are in the hydropower plant to
generate electricity.

15. Parts of a Pelton Wheel Turbine:
• A Pelton wheel turbine consists of four-major
parts and those are:
• Nozzle
• Runner and buckets
• Casing and
• Breaking jet

20. • Nozzle:
• The amount of water striking the buckets of the runner is controlled by providing a spear in the
nozzle.
• The speed is a conical needle which is operated either by a hand wheel or automatically in an axial
direction depending upon the size of the unit.
• When the spear is pushed forward into the nozzle and the amount of water striking the runner is
reduced. On the other hand, if the sphere is pushed back, the amount of water striking the runner
increases.
• Runner and buckets:
• The runner or blade consists of a circular disc on the Periphery of which several buckets evenly
spaced are fixed. The Shape of the bucket is of a double hemispherical cup or bowl. Each bucket is
divided into two symmetrical parts by a dividing wall which is known as a splitter.
• The jet of water strikes on the splitter. The splitter divides the jet into two equal parts and the Jets
come out at the outer edge of the bucket. The bucket is shaped in such a way that the jet gets
deflected through 160 degrees or 170 degrees.
• The bucket is made of cast iron, cast Steel bronze or stainless steel depending upon the head at the
inlet of the turbine
• Casing:
• The function of the casing is to prevent the splashing of the water and to discharge water to the
tailrace. It also acts as a safe ground against accidents. It is made of cast iron or fabricated steel
plates. The casing of the Pelton wheel does not perform any hydraulic function.
• Breaking jet:
• When the nozzle is completely closed by moving the spear in the forward direction, the amount of
water striking the runner reduces to zero. But the runner due to inertia goes on revolving for a long
time. To stop the runner in a short time, a small nozzle is provided which directs the jet of water on
the back of the vanes. This jet of water is called breaking jet.

21. advantages of Pelton Wheel:
• These are some advantages of Pelton Wheel Turbine:
• The Pelton turbine is the most efficient of hydro turbines.
• It operates with a very flat efficiency curve
• Each bucket splits the water jet in half, thus balancing the side-load forces or thrust
on the wheel and thus the bearings.
• It operates on the high head and low discharge.
• It has a tangential flow which means that it can have either axial flow or radial
flow.
• Pelton wheel turbine is very easy to assemble.
• There is no cavitation because water jet strikes only a specific portion of the runner.
• It has fewer parts as compared to Francis’s turbine which has both fixed vanes and
guided vanes.
• The overall efficiency of the Pelton turbine is high.
• Pelton wheel turbines, both first law and the second law of motion are applied.
• The main advantages are that In this turbine, the whole process of water jet
striking and leaving for the runner takes place at atmospheric pressure.

22. • Disadvantages of Pelton Wheel:
• And these are some disadvantages of Pelton
Wheel Turbine:
• The efficiency decrease very quickly with time.
• The Turbine size runner, generator and
powerhouse required is large.
• The variation in the operating head is difficult
to control because of high heads.

23. What is a Francis Turbine?
• Francis turbine definition is a combination of both impulse
and reaction turbine, where the blades rotate using both
reaction and impulse force of water flowing through them
producing electricity more efficiently. Francis turbine is
used for the production of electricity most frequently in
medium or large-scale hydropower stations.
• These turbines can be used for heads as low as 2 meters
and as high as 300 meters. Additionally, these turbines are
beneficial as they work equally well when positioned
horizontally as they do when they are oriented vertically.
The water going through a Francis turbine loses pressure,
but stays at more or less the same speed, so it would be
considered a reaction turbine

24. • Major Components of Francis Turbines With
Diagram
• Spiral Casing
• Stay Vanes
• Guide Vanes
• Runner Blades
• Draft Tube

25. Francis Turbine Working Principle
With Diagram
• Francis turbines are employed regularly in hydroelectric power plants. In these power plants, high-
pressure water enters the turbine through the snail-shell casing (the volute). This movement
decreases the water pressure as it curls through the tube; however, the water’s speed remains
unchanged. Following the passing through the volute, the water flows through the guide vanes and
is directed towards the runner’s blades at optimum angles. Since the water crosses the precisely
curved blades of the runner, the water is diverted somewhat sideways. This makes the water lose
some part of its “whirl” motion. The water is also deflected in the axial direction to exit a draft
tube to the tail race.
• The mentioned tube reduces the water’s output velocity to gain the maximum amount of energy
from the input water. The process of water being diverted through the runner blades results in a
force that propels the blades to the opposite side as the water is deflected. That reaction force (as
we know from Newton’s third law) is what makes power to be carried from the water to the
turbine’s shaft, continuing rotation. Since the turbine moves due to that reaction force, Francis
turbines are identified as reaction turbines. The process of altering the direction of the water flow
also decreases the pressure within the turbine itself.
• Francis turbines are the most favored hydraulic turbines. These turbines are the most stable
workhorse of hydroelectric power stations. Francis turbine supplies about 60 percent of the global
hydropower capacity, mainly because it can work efficiently under a wide range of working
conditions. You can find the working principle of the Francis turbine here.

26. • Francis Turbine Advantages
• No head failure occurs still at the low discharge of water.
• Francis turbine variation in the operating head can be more
simply controlled.
• The runner size is small.
• The ratio of utmost and least operating head can be even
two in these turbines.
• Francis type units cover a wide head range, from 20 to 700
M and their output varies from a few kilowatts to 200
megawatts
• The 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.

27. Disadvantages of Francis Turbine:
• Despite all the mentioned pros, there are some cons in
using Francis turbines. These disadvantages are listed
here:
• The water contains pollutants which may cause
extremely rapid wear in a Francis turbine.
• Francis turbine is highly expensive.
• It has a simple operation but a very complex design.
• The number of moving parts in this kind of turbine is
considerable.
• The runner is not available commonly since it has a
standard spiral casing.
• It has costly and complicated maintenance.
• It faces the hazard of cavitation.
• Current losses in the Francis turbine are inevitable.

28. Work Done and Efficiency in Francis
Turbine:
In order to find the efficiencies, we
should be familiar with the velocity
triangle in the Francis turbine. Here,
the velocity triangle and some
applicable formulas about the Francis
turbine are presented.

29. Kaplan Turbine
• This Kaplan Turbine was developed in 1913 by
Viktor Kaplan, an Austrian Professor. In his
design, he combined automatically adjusted
propeller blades and guided vanes to obtain
efficiency over a wide range of water flow.

30. Definition of Kaplan Turbine:
• Kaplan turbine is an axial flow reaction
turbine which is suitable for low heads and
hence requires a large quantity of water to
develop a large amount of power.
• It is more compact then Francis turbine which
can run faster and maintains high efficiency.
The Kaplan Turbine is located between the
high-pressure water source and the low-
pressure water exit.

31. • Components of the Kaplan Turbine:
• The main components of a Kaplan turbine are:
• Scroll Casing
• Guide Vanes and Guide Mechanism
• Runner, Runner Blades, and Guide Vanes
• Draft Tube

32. • 1. Scroll Casing:
• The inlet is through the scroll casing which is in the
form of a spiral. This ensures constant velocity of water
flows along the path after entering into the casing.
• 2. Guide Vanes and Guide Mechanism:
• Water gets distributed by the guide vanes and can flow
on to the runner blades in an axial direction. The
blades are so shaped that water flows axially through
the runner.
• 3. Runner, Runner Blades, and Guide Vanes:
• The runner blades, as well as guide vanes, are
adjustable while the turbine is in motion. Guide vanes
are turned through a certain angle to regulate the flow.
The axial flow of water acting on the runner vanes
causes the runner to rotate.

35. • 4. Draft Tube:
• Finally, water is discharged to the tailrace
through a gradually expanding tube called the
Draught tube. A Kaplan Turbine runner has 4
to 6 blades.
• When both the Guide vanes angle and the
Runner blade angle may thus be varied, higher
efficiency can be maintained over a wide
range of operating conditions.

36. Working Principle of Kaplan Turbine:
• The water from the penstock is to be allowed
into the scroll casing of the Kaplan Turbine.
The scroll casing is designed in such a way that
the pressure flow is maintained.
• The two types of blades which are used in this
turbine are Guide Vanes and Runner blades

37. • The Guide vanes are fixed along with the spiral casing
which makes the water to flow on to the runner
whereas the runner blades are fixed to the Hub or
Boss(runner) which rotates due to the reaction force of
water hitting the blades of the runner.
• The guide vanes are adjustable w.r.t the flow rate. The
water takes a 90-degrees turn so that the direction of
the water is axial to that of runner blades.
• From the runner blades, the water enters into the draft
tube where its pressure energy and kinetic energy
decreases.
• Kinetic energy is gets converted into pressure energy
results in increased pressure of the water.
• Due to the rotation of the runner, the shaft of the
turbine rotates which thereby generates electricity.

39. • Applications of Kaplan Turbine:
• The applications of Kaplan Turbine are as follows.
• Kaplan turbines are widely used for electrical power
production.
• It can work more efficiently at low heads and high flow
rates.
• Its construction is very easy because of the smaller
size.
• The efficiency of the Kaplan turbine is very high when
compared to other hydraulic turbines.

40. Advantages of the Kaplan Turbine:
• The advantages of Kaplan Turbine are as follows.
• Easy in construction
• The Kaplan turbine requires less space
• The efficiency of the Kaplan turbine is very high compared
to others.
• At the lower head, this Kaplan turbine works much
efficiently.
• The number of blades are less in this turbine.
• Disadvantages of the Kaplan Turbine:
• The disadvantages of Kaplan Turbine are as follows.
• The disadvantage of the Kaplan turbine is "cavitation",
which occurs due to the pressure drop in the draft tube.
• The stainless steel as a material to the runner blades may
reduce the problem of cavitation to some extent.

41. •What is a Draft Tube?
• A draft tube is a type of tube that connects the
exit of the water turbine to the tailrace.
• The tailrace is the water channel that takes the
water out of the turbine.
• It is usually located at the outlet or exit of the
turbines and converts the kinetic energy of the
water at the outlet of the turbine to static
pressure.
• The materials used to create a draft tube are cast
steel and cemented concrete.

43. Types of Draft Tube
• Various forms of draft tubes are available.
There are mainly 4 types of draft tube, and
those are:
• Conical draft tube
• Simple elbow draft tube
• Moody spreading draft tube
• Elbow draft tube with a varying cross-section

47. • draft tube function
• The primary function of the draft tube is to control the flow
of water. The turbine has a tailrace.
• The turbine is attached to this tailrace by the tube, causing
the turbine to be beyond the water but still have access to
the water.
• It requires the negative head to be formed at the outlet of
the runner and hence raises the net head of the turbine.
• The turbine can be mounted above the tailrace without
any lack of net head and thus the turbine may be
adequately inspected.
• Moreover, it transforms a significant portion of the kinetic
energy wasted at the outlet of the turbine into usable
pressure energy. Without a draft tube, the kinetic energy
rejected at the outlet of the turbine would be lost to the
tailrace.
• The draft tube stops the water from splashing out of the
runner and leads the water to the tailrace.

48. Draft Tube efficiency
• The efficiency of the draft tube is the ratio of
kinetic power transfer to the kinetic energy
available at the inlet to the draft tube. The
efficiency of a tube depends on how much of
the kinetic energy of the water is converted
into pressure energy. The more energy is
converted, the more efficient the draft tube
can be.

50. Cavitation:
• Cavitation is a vital problem in hydraulic machines that negatively
influences their performance and may cause damages. Cavitation is
a phenomenon that manifests itself in the pitting of the metallic
surfaces of turbine parts because of the formation of cavities. The
reaction turbines operate under the low and medium head at a
high specific speed and operate under variable pressure are prone
to cavitation.
• Cavitation in hydraulic machines negatively affects their
performance and may cause severe damages. These damages can
be summarized below:
• Erosion of material in turbine parts.
• Distortion of blade angle.
• Efficiency losses due to distortion or erosion

54. https://theconstructor.org/water-
resources/surge-tank-types-
function/12946/

55. • Governing of turbines
• We have already understood that hydraulic turbines are basically defined
as the hydraulic machines which convert hydraulic energy in to mechanical
energy and this mechanical energy will be given to a generator to produce
the electric energy. Generator will be directly coupled with the hydraulic
turbine.
•
• In order to maintain the constant frequency of electric power output, the
rotor of the turbine has to rotate with a constant speed and therefore it is
needed to maintain the constant rotational speed of the turbine rotor.
•
• Now we must understand here that how to maintain the constant
rotational speed of the turbine rotor.
•
•

56. • Rotational speed of rotor of a turbine will be dependent over the
driving torque and resisting torque.
• Driving torque will be provided by fluid flowing through the blade
passages by its change of angular momentum and resisting torque
will come from the electrical load.
•
• Balance between these two types of torque i.e. driving torque and
resisting torque will enable the rotator of turbine to rotate at
constant angular speed.
•
• When electrical load will be changed, electrical load might be
increased or decreased depending on demand, speed of rotor of
turbine will be changed if there is no provision to change the driving
torque. Hence, frequency of electric power output will be changed
due to change in rotational speed of rotor of turbine and it is not a
desirable result.

57. Let us take one case where electrical load is increased. Let us think what will happen due to
increase in electrical load. Resisting torque will be increased and therefore for a given driving
torque, speed of rotation of rotor of turbine will be decreased. In this case it will be required
to increase the driving torque to boost up the rotational speed of rotor up to its original
speed.
Suppose if electrical load is decreased then will happen. Resisting torque will be decreased
and therefore for a given driving torque, speed of rotation of rotor of turbine will be
increased. In this case it will be required to decrease the driving torque to reduce the
rotational speed of rotator up to its original speed.

58. Therefore in order to restore the initial speed of rotation of rotor of turbine, we
need to change the driving torque up to the desired value of resisting torque which
is changed due to change in electrical load.
As we know that energy given to the rotor of the turbine will be directionally
proportional to the fluid flow rate, therefore change in driving torque will be done
by change in fluid flow rate.
If electrical load is increased, it will be required to increase the driving torque to
boost up the rotational speed of rotor up to its original speed and driving torque
will be increased by increasing the fluid flow rate.

59. • If electrical load is decreased, it will be required to decrease the driving torque to
reduce the rotational speed of rotator up to its original speed and driving torque
will be decreased by decreasing the fluid flow rate.
•
• Therefore, by controlling the fluid flow rate, driving torque could be changed to
meet with the resisting torque to maintain the constant speed of rotation of rotor
of turbine in order to produce the constant frequency of electrical power output.
•
• This is the basic principle behind the governing of all type of turbine. This process
by which the speed of rotation of turbine rotor is kept constant will be termed as
governing of a turbine.
•
• Governing of a turbine is very necessary as a turbine is directly coupled with
electrical generator which is required to run at constant rotational speed in order
to produce the constant frequency of electrical power output.

60. • https://clubtechnical.com/unit-quantities-of-
a-turbine