Classification of Turbines

Turbines - Classifications
Prepared by
Prof. S. G. Taji
Dept. of Civil Engineering
S.R.E.S’s Sanjivani College of Engineering,
Kopargaon

TURBINES
Turbines are the hydraulic machines
which convert hydraulic energy into
mechanical energy.
HYDRAULIC
ENERGY
TURBINES
MECHANICAL
ENERGY

Working Principle
 The working principle is very much simple.
 When the fluid strikes the blades of the turbine, the
blades are displaced, which produces rotational energy.
 The turbine shaft is directly coupled to an electric
generator.
 Generator converts mechanical energy into electrical
energy.
 This electrical power is known as hydroelectric power.

According to
the Type of
Energy at
Inlet
Impulse
Reaction
Direction Of
Flow Through
Runner
Tangential
flow turbine
Radial flow
turbine
Axial flow
turbine
Mixed flow
turbine.
According To
the Head at the
Inlet of Turbine
High head
turbine
Medium head
turbine
Low head
turbine
According to
the specific
speed of the
turbine
High specific
speed
turbine
Medium
specific
speed
turbine
Low specific
speed
turbine
Classification of Turbines

Impulse Turbine
 If at the inlet of turbine the energy available
is only kinetic energy, the turbine is known
as Impulse Turbine.

Types of Impulse Turbines
I. Pelton Turbine
II. Cross-flow Turbine

Pelton Turbine
 It was invented by Lester Ella Pelton in the 1870s.
 Pelton turbine is suitable for high head and low
flow rate.
 Energy available at the inlet of the turbine is only
kinetic energy. Pressure at the inlet & outlet is
atmospheric.

Cross-flow Turbine
 It is developed by Anthony Michel, in
1903 and is used for low heads. (10–70
meters)
 As with a water wheel, the water is
admitted at the turbine's edge. After
passing the runner, it leaves on the
opposite side.
 Going through the runner twice provides
additional efficiency.
 The cross-flow turbine is a low-speed
machine that is well suited for locations
with a low head but high flow.

Reaction Turbine
 If at the inlet of turbine water possesses kinetic energy
as well as pressure energy, the turbine is known as
Reaction Turbine.
 In a reaction turbine, forces driving the rotor are
achieved by the reaction of an accelerating water flow in
the runner while the pressure drops.

 Types of Reaction Turbines
 Kaplan Turbine
 Francis Turbine
 Kinetic Turbine

Francis Turbine
 The Francis turbine is a type of water turbine that was
developed by James B. Francis and are used for
medium head(45-400 m) and medium discharge.(10-
700 m^3/s)
 The Francis turbine is a type of reaction turbine, a
category of turbine in which the working fluid comes
to the turbine under immense pressure and the energy
is extracted by the turbine blades from the working
fluid.
 The turbine's exit tube is shaped to help deaccelerate
the water flow and recover the pressure.

Kaplan Turbine
 The Kaplan turbine is a water turbine which
has adjustable blades and is used for low heads
and high discharges.
 It was developed in 1913 by the Austrian
professor Viktor Kaplan.
 The Kaplan turbine having drop height: 10 -
700 m and Flow rate 4 - 55 m3/s

 If water flows along the tangent of runner, the
turbine is known as Tangential flow turbine.
 If the water flows in radial direction through the
runner,the turbine is known as Radial flow
turbine.
 If the water flows from outward to inward radially,the
turbine is known as Inward radial flow turbine.
 If the water flows from inward to outward radially,the
turbine is known as Outward radial flow turbine.
 If water flows along the direction parallel to the axis
of rotation of runner, the turbine is known as Axial
flow turbine.
 If water flows in radial direction but leaves in the
direction parallel to the axis of rotation,the turbine
is known as Mixed flow turbine.
According to Direction Of Flow Through Runner

If the water flows
from outward to
inward the turbine is
known as Inward
radial flow turbine.
If the water flows
from inward to
outward the turbine
is known as Outward
radial flow turbine.

 Very High Heads (350m and above): Pelton Turbine
 High Heads (150 m to 350 m): Pelton or Francis
turbine
 Medium Heads (60 m to 150 m): a Francis turbine
 Low Heads (below 60m): Kaplan turbine
According to Head Available

According to Specific Speed
Turbine Specific Speed Remark
Pelton Wheel
With single jet
8.5 to 30
Upto 43 with
double jet
Francis Turbine 50 to 340 --
Kaplan Turbine 255 to 860 --

Summary of Classification
1. According to type of energy at Inlet
a) Impulse Turbine - Pelton Wheel
(Requires High Head and Low Rate of Flow)
a) Reaction Turbine - Fancis, Kaplan
(Requires Low Head and High Rate of Flow)
2. According to direction of flow through runner
a) Tangential Flow Turbine Pelton Wheel
b) Radial Flow Turbine Francis Turbine
c) Axial Flow Turbine Kaplan Turbine
d) Mixed Flow Turbine Modern Francis Turbine

3. According to Head at Inlet of turbine
4.According to Specific Speed of Turbine
a) Low Specific Speed Turbine - Pelton Wheel
b) Medium Specific Speed Turbine - Fancis Turbine
c) High Specific Speed Turbine - Kaplan Turbine
a) High Head Turbine - Pelton Wheel
b) Medium Head Turbine - Fancis Turbine
c) Low Head Turbine - Kaplan Turbine

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

Turbine Efficiencies
1) Hydraulic Efficiency:
Power Delivered To Runner / Power Supplied at Inlet
R.P. / W. P.
2) Mechanical Efficiency:
Power at the Shaft of the Turbine / Power Delivered To
Runner
S. P. / R.P.
2) Overall Efficiency:
Power available at Shaft of Turbine / Power Supplied
at Inlet OR Shaft Power / Water Power
S. P. / W.P. OR (He * Me)

Factors governing the Selection of turbine
 The following points should be considered while
selecting right type of hydraulic turbines for
hydroelectric power plant.
1) Specific speed:
 High specific speed is essential where the head is
low and output is large, because otherwise the
rotational speed will be low which means cost of
turbo-generator and powerhouse will be high.
 On the other hand there is practically no need of
choosing a high value of specific speed for high
installations, because even with low specific speed
high rotational speed can be attained with medium
capacity plants.

2) Rotational speed:
 Rotational speed depends upon specific speed.
Also the rotational speed of an electrical
generator with which the turbine is to be
directly coupled depends on the frequency and
number of pair of poles.
 The value of specific speed adopted should be
such that it will give the synchronous speed of
the generator.
3) Efficiency:
 The efficiency selected should be such that it
gives the highest overall efficiency of various
conditions.

4) Part load operation:
 In general the efficiency at part loads and overloads is less
than that with rated (design) parameters. For the sake of
economy the turbine should always run with maximum
possible efficiency to get more revenue.
 When the turbine has to run at part or overload conditions
Deriaz turbine is employed. Similarly, for low heads,
Kaplan turbine will be useful for such purposes in place of
propeller turbine.
5) Cavitations:
 The installation of water turbines of reaction type over the
tailrace is effected by cavitations.
 The critical values of cavitations indices must be obtained
to see that the turbine works in safe zone.
 Such values of cavitations indices also affect the design of
turbine, especially of Kaplan, propeller and bulb types.

7) Available head and its fluctuation:
 a) Very high (350m and above): for heads greater than
350m, Pelton Turbine is generally employed and
practically there is no any choice except in very special
cases.
 b) High heads (150 m to 350 m): in this range either
Pelton or Francis turbine may employ. For higher
specific needs Francis turbine is more compact and
economical than the Pelton turbine that for the same
working conditions would have to be much bigger and
rather cumbersome.

 c) Medium heads (60 m to 150 m): a Francis
turbine is usually employed in this range.
Whether a high or low specific speed would be
used depends on the selection of the speed.
 d) Low heads (below 60m): between 30m to
60m both Kaplan and Francis turbines may
be used. Francis is more expensive but yields
higher efficiency at part loads and over loads.
 It is therefore preferable for variable loads.
 Kaplan turbine is generally employed less than
30m. Propeller turbines are however,
commonly used for heads up to 15m. They are
adopted only when there is practically no load
variation.

7) Deposition of turbine shaft:
 Experience has shown that the vertical shaft
arrangement is better for large-sized reaction
turbines, therefore, it is almost universally adopted,
whereas, in case of large size impulse turbines,
horizontal shaft arrangement is preferable.
8) Water quality: (i.e. sand content chemical or
other impurities)
 Quality of water is more crucial for the reactive
turbine. Reactive turbine may undergo for rapid
wear in high head.

Performance of Turbines under unit quantities

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

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.

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.

Causes of Cavitation
The liquid enters hydraulic turbines at high pressure; this pressure is
a combination of static and dynamic components.
Dynamic pressure of the liquid is by the virtue of flow velocity and
the other component, static pressure, is the actual fluid pressure which
the fluid applies and which is acted upon it.
 Static pressure governs the process of vapor bubble formation or
boiling.
Thus, Cavitation can occur near the fast moving blades of the
turbine where local dynamic head increases due to action of blades
which causes static pressure to fall.
Cavitation also occurs at the exit of the turbine as the liquid has lost
major part of its pressure heads and any increase in dynamic head will
lead to fall in static pressure causing Cavitation.

Avoiding Cavitation
To avoid cavitation while operating Hydraulic
Turbines parameters should be set such that at any
point of flow static pressure may not fall below the
vapor pressure of the liquid.
These parameters to control cavitation are pressure
head, flow rate and exit pressure of the liquid.
The control parameters for cavitation free operation
of hydraulic turbines can be obtained by conducting
tests on model of the turbine under consideration.
The parameters beyond which cavitation starts and
turbine efficiency falls significantly should be avoided
while operation of hydraulic turbines.

Other Methods to avoid Cavitations

Classification of Turbines

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