1. Q1. Give the detailed classification of hydraulic turbines.
Ans1. Classification of Hydraulic Turbines: Based on flow path
Water can pass through the Hydraulic Turbines in different flow paths. Based on the flow path of
the liquid Hydraulic Turbines can be categorized into three types.
1. Axial Flow Hydraulic Turbines: This category of Hydraulic Turbines has the flow path of
the liquid mainly parallel to the axis of rotation. Kaplan Turbines has liquid flow mainly in
axial direction.
2. Radial Flow Hydraulic Turbines: Such Hydraulic Turbines has the liquid flowing mainly
in a plane perpendicular to the axis of rotation.
3. Mixed Flow Hydraulic Turbines: For most of the Hydraulic Turbines used there is a
significant component of both axial and radial flows. Such types of Hydraulic Turbines are
called as Mixed Flow Turbines. Francis Turbine is an example of mixed flow type, in Francis
Turbine water enters in radial direction and exits in axial direction.
None of the Hydraulic Turbines are purely axial flow or purely radial flow. There is always a
component of radial flow in axial flow turbines and of axial flow in radial flow turbines.
Classification of Hydraulic Turbines: Based on pressure change
One more important criterion for classification of Hydraulic Turbines is whether the pressure of
liquid changes or not while it flows through the rotor of the Hydraulic Turbines. Based on the
pressure change Hydraulic Turbines can be classified as of two types.
1. Impulse Turbine: The pressure of liquid does not change while flowing through the rotor of
the machine. In Impulse Turbines pressure change occur only in the nozzles of the machine.
One such example of impulse turbine is Pelton Wheel.
2. Reaction Turbine: The pressure of liquid changes while it flows through the rotor of the
machine. The change in fluid velocity and reduction in its pressure causes a reaction on the
turbine blades; this is where from the name Reaction Turbine may have been derived.
Francis and Kaplan Turbines fall in the category of Reaction Turbines.
According to the head at the inlet of the turbine
a. High head turbine
b. Medium head turbine
c. Low head turbine
According to the specific speed of turbine
(a) Low specific speed turbine.
(b) Medium specific speed turbine
(c) High specific speed turbine.
Q2. Draw the neat sketch of Pelton turbine and discuss it’s working and construction and
their main parts.
Ans.2 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

2. pressure available at the inlet and the outlet is atmospheric.
The main components of a Pelton turbine are:
(i) 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. 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.
(ii) 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 ( ) 160-1700
.
(iii) 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.
(iv) Breaking jet:
Even after the amount of water striking the buckets is comple tely 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 i s called as breaking jet.

3. WORKING:
Working principle of Pelton turbine is simple. When a high speed water jet injected through a
nozzle hits buckets of Pelton wheel; it induces an impulsive force. This force makes the turbine
rotate. The rotating shaft runs a generator and produces electricity.
Nozzles direct forceful, high-speed streams of water against a rotary series of spoon-shaped
buckets, also known as impulse blades, which are mounted around the circumferential rim of a
drive wheel—also called a runner.
As the water jet impinges upon the contoured bucket-blades, the direction of water velocity is
changed to follow the contours of the bucket. Water impulse energy exerts torque on the bucket-
and-wheel system, spinning the wheel; the water stream itself does a "u-turn" and exits at the
outer sides of the bucket, decelerated to a low velocity. In the process, the water jet's momentum
is transferred to the wheel and thence to a turbine. Thus, "impulse" energy does work on the
turbine.
A very small percentage of the water jet's original kinetic energy will remain in the water, which
causes the bucket to be emptied at the same rate it is filled, (see conservation of mass) and
thereby allows the high-pressure input flow to continue uninterrupted and without waste of
energy.
Typically two buckets are mounted side-by-side on the wheel, which permits splitting the water
jet into two equal streams (see photo). This balances the side-load forces on the wheel and helps
to ensure smooth, efficient transfer of momentum of the fluid jet of water to the turbine wheel.
Q3. In case of a Pelton turbine, two hemispherical cup are joined together and water is
directed at the junction. What is the advantage of this arrangement? Under what
conditions would you use more runner for a Pelton turbine?
Ans. 3 In pelton wheel each bucket is divided vertically into two parts by a splitter that has a
sharp edge at the centre and the buckets look like a double hemispherical cup. The striking Jet of
water is divided into two parts by the splitter and each part of the jet flows side ways round the
smooth inner surface of the bucket and leaves it with relative velocity almost opposite in
direction to the original jet. Water jet is split into 2 equal components with help of a splitter. The
special shape of bucket makes the jet turn almost 180 degree. This produces an impulsive force
on bucket. Force so produced can easily be derived from Newton’s 2nd law of motion. Blade

4. outlet angle close to 180o
is usually used in order to maximize impulsive force. A cut is provided
on bottom portion of buckets. This makes sure that water jet will not get interfered by other
incoming buckets.
Q4. Draw neat sketch of Francis Turbine. Describe briefly construction & working of
Francis Turbine.
Ans.4 Construction:
A Francis turbine consists of the following main parts:
Spiral Casing: The spiral casing around the runner of the turbine is known as the volute
casing or scroll case. All throughout its length, it has numerous openings at regular intervals to
allow the working fluid to impound on the blades of the runner. These openings convert the
pressure energy of the fluid into momentum energy just before the fluid impound on the blades
to maintain a constant flow rate despite the fact that numerous openings have been provided for
the fluid to gain entry to the blades, the cross-sectional area of this casing decreases uniformly
along the circumference.
Guide or Stay Vanes: The primary function of the guide or stay vanes is to convert the pressure
energy of the fluid into the momentum energy. It also serves to direct the flow at design angles to
the runner blades.
Runner Blades: Runner blades are the heart of any turbine as these are the centers where the
fluid strikes and the tangential force of the impact causes the shaft of the turbine to rotate and
hence electricity is produced. In this part one has to be very careful about the blade angles at
inlet and outlet as these are the major parameters affecting the power production.
Draft tube: The draft tube is a conduit which connects the runner exit to the tail race where the
water is being finally discharged from the turbine. The primary function of the draft tube is to
reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet.
This permits the turbine to be set above the tail water without any appreciable drop of available
head.
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. 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.

5. 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.
Q5. Explain purpose of providing scroll casing & guide vanes for a hydraulic reaction
turbine.
Ans5.
Purpose of Guide or Stay vane:

6. The basic purpose of the guide vanes or stay vanes is to convert a part of pressure energy of the
fluid at its entrance to the kinetic energy and then to direct the fluid on to the runner blades at the
angle appropriate to the design. Moreover, the guide vanes are pivoted and can be turned by a
suitable governing mechanism to regulate the flow while the load changes. The guide vanes are
also known as wicket gates. The guide vanes impart a tangential velocity and hence an angular
momentum to the water before its entry to the runner. The flow in the runner of a Francis turbine
is not purely radial but a combination of radial and tangential. The flow is inward, i.e. from the
periphery towards the centre. The height of the runner depends upon the specific speed. The
height increases with the increase in the specific speed. The main direction of flow change as
water passes through the runner and is finally turned into the axial direction while entering the
draft tube.
Purpose of Scroll Casing:
The spiral casing around the runner of the turbine is known as the volute casing or scroll case.
All throughout its length, it has numerous openings at regular intervals to allow the working fluid
to impound on the blades of the runner. These openings convert the pressure energy of the fluid
into momentum energy just before the fluid impound on the blades to maintain a constant flow
rate despite the fact that numerous openings have been provided for the fluid to gain entry to the
blades, the cross-sectional area of this casing decreases uniformly along the circumference.
Q.6 Explain construction & working of Kaplan turbine with neat sketch.
Ans.6 The Kaplan turbine is a propeller-type water turbine which has adjustable blades. It was
developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically
adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a
wide range of flow and water level.
Kaplan turbines are now widely used throughout the world in high-flow, low-head power
production.

7. KAPLAN TURBINE
A Kaplan turbine is basically a propeller with adjustable blades inside a tube. It is an axial-flow
turbine, which means that the flow direction does not change as it crosses the rotor.
The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power
production in low-head applications that was not possible with Francis turbines. The head ranges
from 10–70 meters and the output from 5 to 200 MW. Runner diameters are between 2 and 11
meters. The range of the turbine rotation is from 79 to 429 rpm.
Kaplan Turbine is an Axial Flow Reaction Turbine. For Axial Flow Turbines, the water flows
through the runner along the direction parallel to the axis of rotation of the runner. Reaction
Turbine means that the water at the inlet of the Turbine possesses Kinetic Energy as well as
Pressure Energy. For Axial Flow Reaction Turbine, the shaft of the turbine is vertical. The lower
end of the shaft is made larger and is called ‘Hub’ or ‘Boss’. The vanes are fixed on the hub and
hence Hub acts as runner for axial flow turbine. The vanes on the Hub are adjustable for Kaplan
Turbine. The specific speed (Ns) of Kaplan turbine ranges from 300 to 600 and is a low head
turbine
CONSTRUCTION:
The main Parts of Kaplan Turbine are:
1. SCROLL CASING
The water from the penstocks enters the scroll casing and then moves to the guide vanes. From
the guide vanes, the water turns through 90° and flows axially through the runner.
2. GUIDE VANE MECHANISM
The Guide Vanes are fixed on the Hub.
3. HUB
For Kaplan Turbine, the shaft of the turbine is vertical. The lower end of the shaft is made larger
and is called ‘Hub’ or ‘Boss’. The vanes are fixed on the hub and hence Hub acts as runner for
axial flow turbine.
4. DRAFT TUBE
The pressure at the exit of the runner of 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

8. gradually increasing area is used for discharging water from the exit of turbine to the tail race.
This tube of increasing area is called Draft Tube. One end of the tube is connected to the outlet
of runner while the other end is sub-merged below the level of water in the tail-race.

9. THEORY OF OPERATION
The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid
changes pressure as it moves through the turbine and gives up its energy. Power is recovered
from both the hydrostatic head and from the kinetic energy of the flowing water. The design
combines features of radial and axial turbines.
The inlet is a scroll-shaped tube that wraps around the turbine's wicket gate. Water is directed
tangentially through the wicket gate and spirals on to a propeller shaped runner, causing it to
spin. The outlet is a specially shaped draft tube that helps decelerate the water and
recover kinetic energy.
The turbine does not need to be at the lowest point of water flow as long as the draft
tube remains full of water. A higher turbine location, however, increases the suction that is
imparted on the turbine blades by the draft tube. The resulting pressure drop may lead
to cavitation.
Variable geometry of the wicket gate and turbine blades allow efficient operation for a range of
flow conditions. Kaplan turbine efficiencies are typically over 90%, but may be lower in very
low head applications.[2]
Because the propeller blades are rotated on high-pressure hydraulic oil bearings, a critical
element of Kaplan design is to maintain a positive seal to prevent emission of oil into the
waterway. Discharge of oil into rivers is not desirable because of the waste of resources and
resulting ecological damage.
APPLICATION
Kaplan turbines are widely used throughout the world for electrical power production. They
cover the lowest head hydro sites and are especially suited for high flow conditions. Inexpensive
micro turbines on the Kaplan turbine model are manufactured for individual power production
with as little as two feet of head.
Large Kaplan turbines are individually designed for each site to operate at the highest possible
efficiency, typically over 90%. They are very expensive to design, manufacture and install, but
operate for decades.
They have recently found a new home in offshore wave energy generation,