Definition of A Turbo Machine

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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

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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.

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• 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.

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General layout of Hydro-Power Plant

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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.

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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

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Efficiencies of Hydraulic Turbines

• 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

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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

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Classification of Turbines
Turbines are classified according to several
considerations as indicated below. i)   Based on
working principle a)  Impulse turbine b) 
Reaction turbine
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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.

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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) Pelton Turbine b)  Medium head
turbine (60 250 m) Francis Turbine c)  Low
head turbine (Below 60 m) Kaplan Turbine
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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 vP /
H5/4 a)  Low specific speed (8.5 30) -
Pelton Turbine b)  Medium specific speed (50
340) - Francis Turbine c)  High specific
speed (255 860) - Kaplan Turbine
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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
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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.

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• 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.