1.BASIC DEFINITION 2.BASIC CLASSIFICATION

3.IMPULSE TURBINE 4.COMPOUNDING

5. REACTION TURBINE 6.

DIFFERENCE BETWEEN IMPULSE AND REACTION

7.ADVANTAGES OF STEAM TURBINE

8.DISADVANTAGES OF STEAM TURBINE

A Steam Turbine is a device that extracts Thermal Energy from pressurized Steam and uses it to do Mechanical Energy on a

rotating output shaft. Steam Turbine is device where Kinetic Energy (Heat)

converted into Mechanical Energy (in shape of rotation). 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 basic cycle for the steam

turbine power plant is the Rankine cycle. The modern Power plant uses the rankine cycle modified to include superheating,

regenerative feed water heating & reheating.

A. ON THE BASIS OF PRINCIPLE OF OPERATION

B. ON BASIS OF DIRECTION OF FLOW

C. ON BASIS OF MEANS OF SUPPLY

D. ON BASIS OF NO. OF CYLINDER

• 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.

• Radial Flow: A turbine may also be constructed so that the steam flow is in a radial direction, either toward or away from the axis. In radial flow, auxiliary turbine such as may be used as a pump drive. The radial turbine is not normally the preferred choice for electricity generation and is usually only employed for small output applications

• Axial Flow: The great majority of turbines, especially those of high power, are axial flow. In such turbines the steam flows in a direction or directions parallel to the axis of the wheel or rotor. The axial flow type of turbine is the most preferred for electricity generation as several cylinders can be easily coupled together to achieve a turbine with a greater output. .

• Tangential flow: In this turbine steam flows in tangential direction.

• 1.Single Pressure- There is single source of supply

• 2.Mixed or dual pressure- There are 2 sources of steam usually used in l.p or h.p stages

• 3. Reheated turbine- During its passage through turbine system may be taken out to be reheated in a reheater incorporated in a boiler and returned at high temperature to be expanded.

1.SINGLE CYLINDER- When all stages of turbine are housed in one casing it is called single cylinder

2.MULTI CYLINDER- In large output turbine, the number of stages needed comes so high that

bearings are required to support the shaft. Under this circumstances multicylinder are used.

• PARTS-• 1. Casing• 2. Nozzle- Pressure energy of Steam is

converted into Kinetic Energy • 3.Turbine Blade – Convert kinetic energy into

mechanical work.• 4.Rotor • 5.Shaft

• PRINCIPLE• In this type, the drop in pressure takes

place in fixed nozzles as well as moving blades. The pressure drops suffered by steam while passing through the moving blades causes a further generation of kinetic energy within these blades, giving rise to reaction and add to the propelling force, which is applied through the rotor to the turbine shaft. The blade passage cross-sectional area is not varied.

• 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. 

PARTS-1.Casing.2.Fixed Blades-Performs the function of Nozzle in Impulse turbine. It directs steam to adjacent moving blade. 3.Moving Blades 4.Shaft 5.Rotor  PRINCIPLE- 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

• 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 compounding 1.Velocity Compounding

2. Pressure Compounding 3.Pressure – Velocity Compounding 

• PRESSURE COMPOUNDING • 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

• Kinetic energy transformed to mechanical work in moving blades. No change in pressure in blades

• Velocity Compounding • 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

• 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

• Pressure Velocity Compounding • 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 1st stage and 2nd stage taken separately are identical to velocity compounded turbine. Combines advantages of pressure and velocity compounding.

Applications of the principles generally called, reaction and impulse often appear in the same turbine, and either is adopted without

hesitation as may best suit a particular design, size of unit, or place in a unit. Impulse turbines of low output are less costly and more

efficient than reaction turbines, but with increase of size these differentials disappear, and in the large sizes there is little to choose as to efficiency or as to cost for equal efficiency. High efficiency is expensive in either type, but it cannot be said that either has any

absolute superiority

• 01) Thermal Efficiency of a Steam Turbine is much higher than that of a steam engine.

• 02) The Steam Turbine develops power at a uniform rate and hence does not required Flywheel.

• 03) If the Steam Turbine is properly designed and constructed then it is the most durable Prime Mover.

• 04) In a steam turbine there is no loss due to initial condensation of steam.

• 05) In Steam Turbine no friction losses are there.

• 1)High efficiency is ordinarily obtained only at high speed.

• 2)Gas turbine locomotives had similar problems, together with a range of other difficulties.

• 3) These devices are heavy and cumbersome.

• 4) Turbines can rotate in only one direction.