Definition of A Turbo Machine
Turbines are energy developing machines. Turbines convert fluid energy into
mechanical energy. The mechanical energy developed by the turbines is used
in running an electric generator, which is directly connected, to the shaft of the
electrical generator.
Earlier days method – wooden wheel
Overshot Wheel
 Had very good efficiency
 Could not handle large quantity of water
Undershot Wheel
 Low Efficiency
General layout of Hydro-Power Plant
a) Reservoir
Reservoirs ensure supply of water through out the year, by storing water
during rainy season and supplying the same during dry season.
b) Dam
The function of the dam is to increase the reservoir capacity and to increase the
working head of the turbine.
c) Penstock
A pipe between dam and turbine is known as penstock. It will carry the water
from dam to turbine. Penstock is commonly made of steel pipes covered with
RCC.
d) Surge tank/Forebay
When the rate of water flow through the penstock is suddenly decreased, the
pressure inside the penstock will increase suddenly due to water hammer
and thereby damage the penstock.
Surge tank/Forebay is constructed between the dam and turbine. It will act
as a pressure regulator during variable loads.
e) Turbine
Turbines convert the kinetic and potential energy of water into mechanical
energy to produce electric power.
f) Generator and Transformer
Electric generator converts mechanical energy into electrical energy. A step
up transformer will increase the voltage for loss free transmission.
General layout of Hydro-Power Plant
Advantages and Disadvantages of HPP
Advantages of hydraulic power plants
 Operating cost is very low
 Less Maintenance cost and less manpower required
 Pollution free
 Quick to start and easy to synchronize
 Can be used for irrigation and flood control
 Long plant life.
Disadvantages of Hydraulic Power Plants
 Initial cost of total plant is comparatively high
 Power generation depends on availability of water
 Cost of transmission is high since most of the plants are in remote areas
 Project duration is long.
Head of Hydraulic Turbines
1) Gross Head


Difference Between the Head race level and Tail race level
Static (No water flow) / Total Head – H1
2) Net or Effective Head
Head available at the entrance of the turbine: H = H1 - hf
a) Net Head for a Reaction Turbine
H = {(P1/w) + (V12/2g) + Z1} – {Z2 + V22/2g)}
b) Net Head for Impulse Turbine
H = {(P1/w) + (V12/2g) + Z1} – Z2
Efficiencies of Hydraulic Turbines
1) Hydraulic Efficiency – due to hydraulic losses
Power developed by the runner
Net power supplied at the turbine entrance
SI Unit:
kW
Metric Unit : Horse Power/Water Horse Power (W.H.P)
2) Mechanical Efficiency – Due to mechanical losses ( bearing friction)
Power available at the turbine shaft (P)
Power developed by the runner
Cont…
3) Volumetric Efficiency – due to amt of water slips directly to the tail race
Amount of water striking the runner
Amount of water supplied to the turbine
4) Overall Efficiency
Power available at the turbine shaft (P)
Net power supplied at the turbine entrance
Classification of Turbines
Turbines are classified according to several considerations as indicated below.
i) Based on working principle
a) Impulse turbine
b) Reaction turbine
Cont…
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.
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.
Cont…
ii) Based on working media
a) Hydraulic turbine
b) Steam turbine
c) Gas turbine
d) Wind Turbine
iii) Based on head
Head is the elevation difference of reservoir water level and D/S water level.
a) High head turbine
(Above 250 m)
b) Medium head turbine (60 – 250 m)
c) Low head turbine
(Below 60 m)
Pelton Turbine
Francis Turbine
Kaplan Turbine
Cont…
iv) Based on specific speed
Turbines can be classified based on Specific Speed. Specific speed is defined
as the speed in rpm of a geometrically similar turbine, which is identical in
shape, dimensions, blade angles and gate openings with the actual turbine
working under unit head and developing unit power. Specific speed is used to
compare the turbines and is denoted by Ns.
Specific speed Ns = N √P / H5/4
a) Low specific speed
(8.5 – 30)
b) Medium specific speed (50 – 340)
c) High specific speed
(255 – 860)
- Pelton Turbine
- Francis Turbine
- Kaplan Turbine
Cont…
v) Based on disposition of turbine main shaft
a) Horizontal shaft
b) Vertical shaft
vi) Based on flow through the runner
a) Radial flow
1. Inward
2. Outward
b) Axial flow
- Kaplan Turbine
c) Mixed flow
- Francis Turbine
d) Tangential flow
- Pelton Turbine
Pelton Wheel Turbine
Design of Pelton Wheel Turbine
 It has a circular disk with cup shaped blades/buckets,
 Water jet emerging from a nozzle is tangential to the circumference of the
wheel.
Working Principle of Pelton Turbine
 Water jets emerging strike the buckets at splitter.
 Stream flow along the inner curve of the bucket and leave it in the direction
opposite to that of incoming jet.
 The high pressure water can be obtained from any water body situated at
some height or streams of water flowing down the hills.
 The change in momentum (direction as well as speed) of water stream
produces an impulse on the blades of the wheel of Pelton Turbine. This
impulse generates the torque and rotation in the shaft of Pelton Turbine.
 Horizontal shaft - Not more than 2 jets are used and
Vertical shaft - Larger no. of jets (upto 6) are used.
 Iron/Steel casing to prevent splashing of water and to lead water to the tail
race.