Steam turbines use the momentum of steam to generate rotary motion. They are classified based on the mode of steam action (impulse or reaction), steam flow direction (axial or radial), exhaust conditions (condensing or non-condensing), steam pressure (high, medium, low), and number of stages (single or multi-stage). An impulse turbine operates using the impulse of steam jets which impinge on turbine blades, changing the steam's direction and generating force. It consists of nozzles that direct high velocity steam onto blades attached to a circular runner, and a casing that contains these components.

5. Steam Turbines
A steam turbine is a prime mover in which rotary
motion is obtained by the gradual change of
momentum of the steam. In general, a steam turbine,
essentially, consists of the following two parts:
1. The nozzle in which 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.
2. The blades/buckets which change the direction of
steam issuing from the nozzle, so that a force acts on
the blades/buckets due to change of momentum and
propel them.

6. The steam turbines may be classified into the following
types:
1. According to the mode of steam action
i. Impulse Turbine
ii. Reaction Turbine
2. According to the direction of steam flow
i. Axial flow turbine
ii. Radial flow turbine
Classification of Steam Turbines

7. Classification of Steam Turbines
3. According to the exhaust condition of steam
i. Condensing turbine
ii. Non-condensing turbine
4. According to the pressure of steam
i. High pressure turbine
ii. Medium pressure turbine
iii. Low pressure turbine
5. According to the number of stages
i. Single stage turbine
ii. Multi-stage turbine

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

9. Impulse Turbine
It has the following main components:
1. Nozzle
2. Runner and blades/buckets
3. Casing

10. 1. Nozzle
i. It is a circular guide mechanism, which guides the
steam to flow at the designed direction and velocity.
ii. It also regulates the flow of steam.
iii. The nozzle is kept very close to the blades, in order
to minimise the losses due to windage.

11. Bucket

12. Nozzle and bucket

13. Working principle of impulse turbine

14. 2. Runner and blades/buckets
i. The runner consists of a circular disc fixed to a
horizontal shaft.
ii. On the periphery of the runner, a number of
blades/buckets are fixed uniformly.
iii. The steam jet impinges on the blades/buckets,
which move in the direction of the jet. This
movement of the blades/buckets makes the runner
to rotate.

15. Blades

17. 3.Casing
1. It is an air-tight metallic case, which contains the
turbine runner and blades/buckets.
2. It controls the movements of steam from the
blades/buckets to the condenser, and does not
permit it to move into the space. Moreover, it is
essential to safeguard the runner against any
accident.