Steam Turbines: Function, Classification, Parts And Working Principle

In this article, I will share with you the function, classification, essential parts and working principle of steam turbines.


A steam turbine is a heat engine simply because it uses heat energy from the steam to perform its work.


So, if you want to understand deeply what a steam turbine does you can check the article that I wrote about a steam power plant.


You might like this: Steam Power Plant: Introduction, Components And Working Principle


The steam turbine is the essential component that leads to the generation of power.


The heat energy from the steam that is generated from the boiler or steam generator can be used to drive the blades of the steam turbine thus causing rotation which results in the production of mechanical energy.


steam turbine, types and working principle

In a steam power plant, the mechanical energy produced by the steam turbine is then connected to a generator that will eventually convert it to electrical energy.


Now that you know the function of the steam turbine, let me share the classification of the steam turbines before I go deeper.


Classification Of Steam Turbines

The classification of the steam turbines depends on the following things;

  1. Construction of the blades.
  2. Methods of using the steam.
  3. Arrangement of the blades.
  4. The steam nozzle of the steam turbines
  5. Steam passages of the steam turbines.


The classification of the steam turbines follows the criteria that I have shared above because of their designs.


Their working principles are similar, but when it comes to how they have been designed to use the steam and their parts that is where they differ.


Let me list down the classifications according to the factors that I have shared above for you to understand what I am talking about.


Classification according to the action of the steam

The steam turbines that are classified according to the action of the steam are as follows;

  • Impulse steam turbine
  • Reaction steam turbine.
  • Impulse and reaction steam turbine (combined steam turbine)


Impulse steam turbine

The impulse steam turbine uses the high velocity of the steam from the stationary nozzles to move the turbines by using force.


The steam after being directed to the steam turbine, first expands in the stationary nozzle to gain its high velocity.


The high velocity steam is released thus hitting the blade in the opposite direction which causes a change in the direction and momentum of the steam.


The action of high velocity against the blades causes an impulsive force on the blades thus making them rotate producing the mechanical energy needed.


The impulse steam turbine converts the energy of the steam into kinetic energy that results in the production of mechanical energy.


Reaction steam turbine

In a reaction steam turbine, there is a change in how the steam energy is used.


The steam from the stationary nozzles with high velocity enters the fast-moving blades.


Further expansion of the steam while moving through the nozzle-shaped blades causes a change in the momentum of the steam and this results in the reaction force on the blades causing them to rotate producing the mechanical energy.


The reaction steam turbine uses the reaction force from the steam to rotate the blades.


Impulse and reaction steam turbines (combined steam turbine)

Commercial steam turbines use both impulse and reaction forces to rotate the blades.


The use of impulsive and reaction forces the steam energy is used sufficiently thus resulting in high operating efficiency of the steam turbine.


These two forces work together in rotating the blades on the same shaft thus producing a higher output.


Classification according to the direction of the steam flow

  • Axial steam turbine.
  • Radial steam turbine.
  • Axial and radial steam turbine (Mixed steam turbine)


Classification according to the pressure of the exhaust

  • Condensing steam turbine.
  • Non-condensing steam turbine.
  • Bleeder steam turbine.


Classification according to the pressure of entering steam.

  • Low-pressure steam turbine.
  • High-pressure steam turbine.
  • Low and high-pressure steam turbine (mixed steam turbine).


Classification according to step reductions.

  • Single stage steam turbine.
  • Multi-stage steam turbine.


Classification according to the method of drive.

  • Direct connected steam turbine.
  • Geared connected steam turbine.


Parts Of The Steam Turbine And Their Functions

These are the essential parts of the steam turbine;

  1. The rotor
  2. The bearings
  3. The metallic casing
  4. The governor
  5. The lubricating oil system


The rotor

This is the part of the steam turbine where the blades or buckets are attached.


The energy from steam energy on the blades (impulse or reaction forces) is what drives the rotor.


Since the blades are attached to the rotor, the efficiency of the rotor depends on the design and construction of the blades.


The bearings

They are used to support the shaft and help it to rotate to transfer energy.


The metallic casing

It’s used to enclose the bearing, rotor, nozzle, blades etc.


It encloses the internal parts of the steam turbine protecting them from damage.


The governor

It’s used to control the supply of steam which ends up decreasing or increasing the speed of the blades thus having an effect on the amount of kinetic energy that will be produced by the steam turbine.


The lubricating oil system

This is the system that is used to oil the steam turbine for its smooth movement, reducing corrosion and preventing it from wear and tear.


Working Principle Of Steam Turbine

The steam is first passed through the nozzles to be expanded and attain its highest velocity. It’s then released from the nozzles and directed against the blades of the steam turbine thus causing its rotation.


The rotation of the steam turbine blades causes the production of mechanical energy through the rotor.


The rotor is then used to drive the shaft that transfers the energy to the essential energy-generating unit.


A steam turbine is a thermal prime mover, so its efficiency is depicted by the heat energy available.


The high-pressure steam is sent into the turbine through the throttle valve which in turn generates the torque energy of the shaft, exhaust steam, extracted steam, mechanical friction and radiation.


The energy generated from the steam turbines depends on the steam pressure and temperature.


And that is why a boiler of lower efficiency can affect the energy generation of the steam turbine.


You might like this: Boilers: Components, Types & Working Principle




This is just a summary of the steam turbine but there is more to learn about this topic.


You need to know the design of different types of steam turbines to be able to differentiate them.


They all work on a similar principle, but their designs are going to differ. It’s important that you get to know how they are constructed.


This just shows you how wide the steam turbine topic is, this is just to give you an overview of what you should expect when you are digging deeper into this unit.


Thanks for reading, if you have any questions, suggestions or additional points just leave your comment. See you in my next article.


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