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STEAM TURBINES
Prepared by,M.S.Steve,
Assistant Professor,Amal Jyothi College of Engineering, Kanjirapally.
Email: [email protected]
Steam Turbines
“Steam Turbine is a prime-mover in which Pressure energy of steam is transformed into Kinetic energy, and later in its turn is transformed into the mechanical energy of rotation of turbine shaft”
Classification based on Principle of Action
1.Impulse Turbine Pressure energy of Steam is converted into Kinetic
Energy. Impulse action of high velocity jet of steam, due to
change in its direction is used to rotate the turbine shaft.
2.Reaction Turbine 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.
Impulse Turbine
1. Casing2. Nozzle – Pressure
energy of Steam is converted into Kinetic Energy
3. Turbine Blade – Convert kinetic energy into mechanical work.
4. Rotor5. Shaft
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
curved vanes Causes change in momentum Impulsive
force on blades. Pressure remains constant when steam
flows through blades. Eg: De Lavel Turbine
Impulse [email protected]
Disadvantages of Impulse Turbine The velocity of Rotor is too high for
practical purpose The velocity of steam leaving the
turbine is considerably high and hence there is a loss in Kinetic Energy
These problems can be overcome by expanding the steam in different stages.
This is known as Compounding.
Reaction Turbine1. Casing2. Fixed Blades• Performs the
function of Nozzle in Impulse turbine.
• It directs steam to adjacent moving blade.
3. Moving Blades4. Shaft5. Rotor
Working 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.
Produces reaction on blades Reaction causes rotor to rotate. Propulsive force causing rotation of turbine
is the reaction force. Hence called reaction turbine.
Eg: Parson’s Turbine
Reaction [email protected]
Compounding of Impulse Turbine
The extreme high speed of Impulse Turbine of the order of 30,000rpm, cannot be directly used for practical purpose. To reduce the speed more than one set of blades are used. This is called compounding.
There are three types of compoundingVelocity CompoundingPressure CompoundingPressure – Velocity Compounding
Velocity Compounding .. 1
1. Nozzle2. Moving Blades3. Fixed Blades4. Rotor5. Shaft
Velocity Compounding .. 2
• Velocity of steam absorbed in stages
• Moving and fixed blades placed alternatively.
• Entire pressure drop takes place in nozzle.
• Kinetic energy of steam converted into mechanical work in 2 stages in figure
Velocity Compounding .. 3
• Velocity reduced to intermediate velocity in the 1st row of moving blades
• Fixed blade direct steam to 2nd set of moving blades.
• Velocity further reduced in 2nd set of moving blades
• Eg: Curtis Turbine
Pressure Compounding ..2
• Pressure energy of steam absorbed in stages.
• Expansion of steam takes place in more than one set of nozzles
• Nozzles followed by set of moving blades
• Pressure energy of steam converted into kinetic energy in nozzles
Pressure Compounding ..3
• Kinetic energy transformed to mechanical work in moving blades.
• No change in pressure in blades.
Pressure Compounding ..4
Pressure Velocity Compounding..1
Combination of pressure compounding and velocity compounding.
In a 2 stage pressure velocity compounded turbine – total drop in steam pressure carried out in 2 stages.
Velocity obtained in each stage is compounded.
Pressure Velocity Compounding..2
Pressure Velocity Compounding..3
1st stage and 2nd stage taken separately are identical to velocity compounded turbine.
Combines advantages of pressure and velocity compounding.
Pressure Velocity Compounding..4
Thank you…!
