WHAT IS STEAM TURBINE ?

The steam turbine is one kind of heat engine machine in which steam's heat energy is converted to mechanical work.The construction of steam turbine is very simple.There is no piston rod,flywheel or slide valves attached to the turbine.So maintenance is quite easy.It consists of a rotor and a set of rotating blades which are attached to a shaft and the shaft is placed in the middle of the rotor.An electric generator known as steam turbine generator is connected to the rotor shaft.The turbine generator collects the mechanical energy from the shaft and converts it into electrical energy.Steam turbine generator also improves the turbine efficiency.

HISTORY OF STEAM TURBINE

The first steam turbine was invented by Greek Mathematician Hero of Alexandria about 120 BC and it was reciprocating type. The modern steam Turbine was made by Sir Charles Parsons in the year 1884.The design has been changed in many times. The capacity of the turbine is coming from 0.75 KW to 1000 MW. It is a wide range of uses such as pumps, compressor etc. Modern steam turbine is also used as a prime mover in a big thermal power plant.

WORKING PRINCIPLE OF STEAM TURBINE

Working principle of steam turbine depends on the dynamic action of steam.A high-velocity steam is coming from the nozzles and it strikes the rotating blades which are fitted on a disc mounted on a shaft.This high-velocity steam produces dynamic pressure on the blades in which blades and shaft both start to rotate in the same direction.Basically,in a steam turbine pressure energy of steam extracts and then it converted into kinetic energy by allowing the steam to flow through thew nozzles.The conversion of kinetic energy does mechanical work to the rotor blades and the rotor is connected to a steam turbine generator which acts as a mediator.Turbine generator collects mechanical energy from the rotor and converts into electrical energy.Since the construction of steam turbine is simple, its vibration is much less than the other engine for same rotating speed.Though different types of governing system are used to improve turbine speed.

TYPES OF STEAM TURBINE

According to the working principle,there are different types of steam turbine.

1. According to the working principle steam turbines are mainly divided into two categories :

   a)Impulse Turbine

   b).Reaction Steam Turbine

⇨When steam strikes the moving blades through nozzles called Impulse Turbine and when it strikes the moving blades under pressure via guide mechanism called Reaction Turbine.

Read working principle of Impulse and Reaction steam turbine.

Steam turbines may be further divided into following categories :

2. According to the direction of steam flow, it may be classified into two categories:-

   a).Axial Flow Steam Turbine:-

   b).Radial Flow Steam Turbine:-

⇨ When the flow of steam inside the casing is parallel to the rotor shaft axis then it is called Axial Flow Steam Turbine and flow of steam inside the casing is radial to the rotor shaft axis called Radial Flow Steam turbine.

3. According to the exhaust condition of steam, it is further divided into two categories:-

   a)Back Pressure or Non-Condensing types Steam Turbine:-

   b)Condensing type Steam Turbine:-

⇨ After expansion of steam it is exhausted into atmosphere called back pressure steam turbine or non-condensing types steam turbine otherwise it exhausted into a condenser called condensing turbine.

4. According to pressure of steam, it may be divided following categories:-

   a)High-pressure or pass-out or Extraction steam turbine:-

 b)Medium-pressure or back pressure steam turbine:-

   c)Low-pressure turbine:-

⇨ High, medium and low-pressure steam is supplied into the turbine, called high-pressure steam turbine or medium pressure steam turbine or back pressure steam turbine and low- pressure steam turbine.These turbines are used for various manufacturing and heating process.

5. According to the number of stages, it may be divided following categories:-

   a)Single stage steam turbine:-

   b)Multi-stage steam turbine:-

⇨ Steam is coming from nozzles when passed through a single set of moving blades called single stage steam turbine and to flow multi-stages of moving blades called multi-stages steam turbine.

6. According to the blade and wheels arrangement, it may be divided following categories:-

   a)Pressure Compounding Steam Turbine

   b)Velocity Compounding Steam Turbine

   c)Impulse-Reaction Combined Steam Turbine

   d)Pressure-Velocity Compounding Steam Turbine

DIFFERENCE BETWEEN STEAM TURBINE AND STEAM ENGINE