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Steam Turbine
A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to
do mechanical work on a rotating output shaft
A device which converts heat energy of to the steam to the mechanical energy which finally
converted into electrical energy
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5 kW (10 hp) of electricity
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Parsons had the satisfaction of seeing his invention adopted for
all major world power stations, and the size of generators had increased from his first 7
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Working of Steam Turbine
Steam turbines are heart of power plant, they are the devices which transform thermal energy in
fluid to mechanical energy
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Energy Absorption from fluid
When high energy fluid (high pressure and high temperature) passes through series of rotor blades, it absorbs
energy from fluid and starts rotating, thus it transforms thermal energy in fluid to mechanical energy
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Energy Transfer to Blades
When fluid passes through rotor blades it loses some amount of energy to the rotor blades
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As kinetic energy comes down velocity of
flow decreases
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So before passing the stream to next rotor stage we have to increase
the velocity first
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When
fluid passes through stator blades velocity of fluid increase due to its special shape thus one part of enthalpy
energy will get converted into kinetic energy
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It is to be noted that here there is no energy addition or removal from flow, what happens here is
conversion of enthaply energy into kinetic energy
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Velocity and enthalpy variation of flow is shown in following figure
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General view of Working Steam Turbine

A closed cycle is formed to utilize the energy in useful work so after high pressure
turbine the low pressure steam goes to the low pressure turbine in this way the
whole cycle proceeds
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One
of such rotor set is shown in figure below
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When flow passes through such airfoils it induces a low pressure on bottom surface and
high pressure on top surface of airfoil as shown in figure below
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So
some part of fluid energy will get transformed to mechanical energy of blade
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Blades used in Turbine

Steam Turbine works on Rankine Cycle
 An ideal Rankine cycle operates between pressures of 30 kPa and 6 MPa
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Find the
net work for the cycle and the thermal efficiency
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Ideal Rankine Cycle
This cycle follows the idea of the Carnot cycle but can be practically implemented
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CLASSIFICATION OF STEAM TURBINE
Classification of steam turbines may be done as following:
1
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According to direction of flow:
(a)Axial flow turbine
(b)Radial flow turbine
3
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According to number of cylinders
(a)Single cylinder turbine
(b)Double cylinder turbine
(c)Three cylinder turbine
(5)According to steam pressure at inlet of Turbine:
(a) Low pressure turbine
(b) Medium pressure turbine
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(b) Nozzle governing turbine
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(7) According to usage in industry:
(a) Stationary turbine with constant speed
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(c) Non stationary turbines
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The common types of steam turbine are
1
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2
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The main difference between these two turbines lies in the way of expanding
the steam while it moves through them
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In the reaction turbine the steam expanded
continuously as it passes over the blades and thus there is gradually fall in the
pressure during expansion below the atmospheric pressure
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Systematic Diagram of Impulse turbine

Reaction Turbine
In this type of turbine, there is a gradual pressure drop and takes place
continuously over the fixed and moving blades
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The reaction turbine consist of a row of stationary blades and the following
row of moving blades
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But the velocity decrease in the moving blades and increases
in fixed blades with change of direction
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It also
concluded that as the volume of steam increases at lower pressures therefore the
diameter of the turbine must increase after each group of blade rings
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 The Steam Turbine develops power at a uniform rate and hence does not
required Flywheel
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 In a steam turbine there is no loss due to initial condensation of steam
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Disadvantages
 High efficiency is ordinarily obtained only at high speed
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 3) These devices are heavy and cumbersome
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Conclusion
The steam turbine is a prime mover in which the potential energy of steam is
transformed into kinetic energy, and then transferred into mechanical energy by the
turbine shaft
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