1. STEAM TURBINES
Steam turbine is a device which is used to convert kinetic energy of steam into mechanical energy.
In this, enthalpy of steam is first converted into kinetic energy in nozzle or blade passages
The high velocity steam impinges on the curved blades and its direction of flow is changed.
This causes a change of momentum and thus force developed drives the turbine shaft
The steam turbine has been used as a prime mover in all steam power plants.

2. STEAM TURBINES
Now – a days, single steam turbine of 1000MW capacity is built in many countries.
In large sizes, it is used for driving electric generator. In small sizes, it is used to drive pumps, fans, compressors

3. Steam turbine -Parts Nozzle:
The heat energy of high pressure steam is converted into kinetic energy, so that the steam issues from the nozzle with a very high velocity
Blades:
The blades which change the direction of steam issuing from the nozzle, so that a force acts on the blades due to change of momentum and propel them

4. Advantages of ST over Reciprocating steam engine
Steam turbine can be rotated with very high speed
The efficiency of S.T is high
The steam consumptions is less
The S.T is compact& requires less space
Frictional loss is less due to lesser sliding parts
Less operating & maintenance cost

5. Classification of steam turbines
According to mode of steam action
1.Impulse turbine
2.Reaction turbine
According to direction of steam flow
1.Axial flow turbine
2.Radial flow turbine
According to exhaust condition of steam
1.Condensing type turbine
2.Non condensing type turbine
According to no of stages
1.Single stage turbine
2.Multi stage turbine
According to pressure of steam
1.High pressure turbine
2.Low pressure turbine
3.Medium pressure turbine

6. Impulse Turbine
An impulse turbine ,as the name indicates, is a turbine which runs by the impulse of steam jet .In this turbine, the steam is first made to flow through a nozzle. Then the steam jet impinges on the turbine blades(which are curved like buckets) and are mounted on the circumference of the wheel.
The steam jet after impinging glides over the concave surface of the blades and finally leave the turbine.

7. Impulse Turbine

8. Components
Nozzle: Runner and blades: Casing:

10. Reaction Turbine

11. In reaction turbine there is no sudden pressure drop
In reaction turbine there is no sudden pressure drop. There is a gradual pressure drop and takes place continuously over the fixed and moving blades.
A number of moving blades are fitted to the rotating shaft. Fixed blades are provided in between such pairs of moving blades
The function of fixed blades is that they guide the steam as well as allow it to expand in a larger velocity. It is similar to that of nozzles as in impulse turbine
The moving blade serves the following functions
It converts the kinetic energy into useful mechanical energy
The steam expands in moving blades and gives reaction to the moving blades

14. Impulse Turbine
Reaction Turbine
It consists of nozzles and moving blades
It consists of fixed and moving blades
Pressure drop occurs in nozzles and not in moving blades
Pressure drop occurs in nozzles and moving blades
Steam strikes the blades with kinetic energy
Steam passes over the blades with pressure and kinetic energy
Blades are of symmetrical type
Blades are of varying cross section
Power developed is less
Power developed is more
It occupies less space for the same power
It occupies more space for the same power output
Velocity of turbine is high
Velocity of turbine is more
Efficiency is less
Efficiency is more
Blade manufacturing is simple as they are of symmetrical cross section
No of stages required are less for the same power developed
Blade manufacturing is difficult as it is of varying cross section
No of stages required are more for the same power developed

15. Compounding
It is the process of increasing the number of nozzle rows and moving blade rows in order to increase the power output and efficiency of the turbine.
Purpose of compounding:
1.To increase the power output of turbine by utilising most of the energy available in the steam
2.To increase the efficiency of the turbine
3.To reduce the exit steam loss

16. Types of compounding Velocity compounding Pressure compounding
Pressure velocity compounding