What is Turbine?
A turbine is a rotary mechanical device that
extracts energy from a fast moving flow of
water, steam, gas, air, or other fluid and
converts it into useful work..
The working principle is very much simple.
When the fluid strikes the blades of the turbine, the blades are
displaced, which produces rotational energy.
When the turbine shaft is directly coupled to an electric gene-
-rator mechanical energy is converted into electrical energy.
This electrical power is known as hydroelectric power.
Basic types of turbines
Although the same principles apply to all turbines,
“Steam Turbine is a prime-mover in which
heat and pressure energy of steam is
transformed into Kinetic energy, and later
in its turn is transformed into the
mechanical energy of rotation of turbine
Working Principle of Steam
The power in a steam turbine is obtained by the rate of change in
momentum of a high velocity jet of steam impinging on a curved
blade which is free to rotate.
The steam from the boiler is expanded in a nozzle, resulting in the
emission of a high velocity jet. This jet of steam impinges on the
moving vanes or blades, mounted on a shaft. Here it undergoes a
change of direction of motion which gives rise to a change in
momentum and therefore a force.
Steam turbines are mostly 'axial flow' types; the steam flows over
the blades in a direction Parallel to the axis of the wheel. 'Radial
flow' types are rarely used.
Classification Based on
Principle oF Action
Pressure energy of Steam is converted into Kinetic
Impulse action of high velocity jet of steam, due to
change in its direction is used to rotate the turbine shaft.
Reaction force due to expansion of high pressure steam
when it passes through a set of moving and fixed blades
is used to rotate the turbine shaft.
Due to expansion of steam, pressure drop occurs
continuously over both fixed and moving blades.
This pressure difference exerts a thrust on the blades.
The resulting reaction force imparts rotary motion.
2. Nozzle – Pressure
energy of Steam is
converted into Kinetic
3. Turbine Blade –
Impulse turbine - Working
High pressure steam from boiler is
supplied to fixed nozzles.
Nozzle – Pressure falls from boiler
pressure to condenser pressure
Reduction in pressure increases velocity.
High velocity steam impinges on moving
Causes change in momentum Impulsive
force on blades.
Pressure remains constant when steam
flows through blades.
function of Nozzle
It directs steam
High pressure steam directly supplied to
turbine blades with out nozzles.
Steam expands(diameter increases) as it
flows through fixed and moving blades
Continuous drop of pressure.
Velocity of steam is increased when it
passes through the fixed blades.
Produces reaction on blades
Reaction causes rotor to rotate.
Propulsive force causing rotation of turbine
is the reaction force. Hence called reaction
Difference b/w Impulse and Reaction
The main difference between
impulse and reaction turbine lies
in the way in which steam is
expanded while it moves throw
them In the former type steam
expands in the nozzle and its
pressure doesn’t change as it
moves over the blades while in
the later types the steam
expands continuously as it
passes over the blades and thus
there is a gradual fall in
pressure during expansion
To maximize the efficiency of steam turbine the
steam is expanded, generating work in a number
Multiple stages turbines are highly efficient.
Most steam turbines use a mixture of both
impulse and reaction design.
Advantages oF Steam
Thermal Efficiency of a Steam Turbine is much higher than that of a
The Steam Turbine develops power at a uniform rate and hence
does not required Flywheel.
If the Steam Turbine is properly designed and constructed then it is
the most durable Prime Mover.
In a steam turbine there is no loss due to initial condensation of
In Steam Turbine no friction losses are there.
Disadvantages oF Steam
High efficiency is ordinarily obtained only at high speed.
Gas turbine locomotives had similar problems, together with a range
of other difficulties.
These devices are heavy and cumbersome.
Turbines can rotate in only one direction.
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. so it is concluded that the steam
turbine is very useful for mechanical work.