MECHANICAL THEORY

Hydraulic Turbines-Classification,Impulse and Reaction Turbine, Layout of Hydroelectric Power Plant

Hydraulic Turbines-Introduction, Classification, Impulse and Reaction Turbine, Layout of Hydroelectric Power Plant: Hydraulic turbines are machines which convert hydraulic energy into mechanical energy. If the machine transforms mechanical energy into hydraulic energy it is called a pump. Thus in turbines, fluid does work on the machine and machine produces power. but, the pump absorbs the power and work is done on the fluid.

The mechanical energy developed is utilized for running an electric generator which is directly coupled to the shaft of the turbine. The electric power developed by the electric generator is known as hydroelectric power. So, the generation of hydroelectric power is cheaper than the other resources like coal, oil, etc.

In general, the principal component of a turbine is a rotor. The rotor is a wheel carrying a number of plates and vanes on its periphery. The rotor is housed in a stationary casing and water possess a good amount of potential energy which is allowed to flow through pipes and finally discharged through nozzles and thus gaining kinetic energy.

Whenever the water strikes the runner and causes it to rotate, the mechanical energy developed is supplied to the generator coupled to the runner which generates electricity.

Classification of Hydraulic Turbines:

The hydraulic Turbines were classified according to the following conditions.

  1. Action of water
  2. The direction of flow of water
  3. Available head
  4. Specific speed

1.Action of water

Impulse: There is no pressure drop on the runner/rotor. K.E of water coming from the jet is used to run the runner/rotor.

Ex: Pelton wheel turbine.

Reaction: There is a loss of K.E as well as pressure energy on the runners of the blade.

 Ex: Francis turbine

2.The direction of flow of water

If the water strikes the blades of the runner tangential to the path of rotation called Tangential flow.

Ex: Pelton wheel turbine.

Radial:  If the water strikes the blades of the runner radially and coming out axially called as Radial flow.

Ex: Francis turbine

Axial: In this flow, the water flows parallel to the axis of the turbine.

Ex: Kaplan turbine

3.Available head

High head: The turbine capable of working under the high potential head of water above 300m

       Ex: Pelton wheel turbine.  

Medium head: The turbine is capable of working under a medium range of potential head about 60m to 300m

       Ex: Francis turbine.

Low head: The turbine is capable of working under a low range of potential head less than 60m

4.Specific speed:

Low Specific Speed: Turbine works in the range of 10-50. (Ex: Pelton wheel turbine)

Medium Specific Speed: Turbine works in the range of 50-350. (Ex: Francis turbine)

High Specific Speed: Turbine works in the range of 250-850. (Ex: Kaplan turbine)

This is the classification of Hydraulic Turbines in a detailed way.


Impulse Turbine V/S Reaction Turbine:

The difference between Impulse Turbine and Reaction Turbine is as follows.

IMPULSEREACTION
Available energy is converted into kinetic energyA major part of available energy is converted to pressure energy
Pressure in the turbine is constantPressure gradually reduces  while water flows on the turbine blades
The wheel and the blades should have accesses to free air and must not run fully.The blades are always under the action of pressure, the wheel must always run fully.
Only one face of the blade is activeBoth sides
Regulation of flow and power is easier without loss of energyDifficult
Used for high headsLow and medium heads
Efficiency is lessEfficiency is more
Energy transfer is a change in energyDue to a change in pressure head

This is the explanation of the Impulse Turbine and Reaction Turbine in a detailed way.


The layout of the Hydro-electric Power Plant:

Generation of electricity by hydropower is one of the best methods of producing electric power.

The Hydro-electric Power plant consists of the following parts.

1.Reservoir and Dam

2.Control Gate

3.Penstock

4.Surge Tank

5.Water Turbine

6.Generator

hydraulic turbines-Hydro-electric power plant
hydraulic turbines-Hydro-electric power plant

Working of Hydro-Electric Power Plant:

The water is traveled from the reservoir passing through the gates, penstock and from the nozzle, it can hit the turbine blades to generate electricity. The water which moves away from the turbine enters into the Afterbay via Tailrace.

So, for the requirement and production of electricity, the components of the hydro-electric power plant were used which were explained below.

1.Reservoir and Dam:

The dam is constructed on a large river in order to ensure sufficient water storage and the dam forms a large reservoir behind it. The height of the water level (called a water head) in the reservoir determines the potential energy stored in it.

Water initially with some potential energy is converted to high-pressure energy during the passage and finally converted into kinetic energy when password through the nozzle of the turbine. This kinetic energy is converted to electrical energy, as the turbine is coupled to an electric generator.

2.Control Gate:

The amount of water released in the penstock can be controlled by a control gate. The maximum amount of water is released through the penstock when the control gate is fully opened.

3.Penstock: 

A penstock is a steel pipe which carries water from the reservoir to the turbine. The potential energy of the water is converted into kinetic energy as it flows down through the penstock due to gravity.

4.Surge Tank:

A surge tank is a small reservoir or tank which is open at the top and is fitted between the reservoir and the powerhouse. The water level in the surge tank rises or falls to reduce the pressure swings in the penstock.

5.Water Turbine:

Water from the penstock is to be traveled to the water turbine and the turbine is coupled to an electric generator. Kinetic energy(K.E.) of the water drives the turbine and consequently, the generator gets driven.

6.Generator:

A generator is placed or mounted in the powerhouse which is coupled to the shaft of the turbine. The passage of water from the nozzle hits the turbine blades which makes the shaft of the turbine to rotate. It drives the generator and electricity is produced.

The produced electricity will be Step up or Step down by means of a transformer and later on it will supply to the domestic and industrial applications.

The water passing through the turbine is discharged to the tailrace which carries water away from the powerhouse after it has been passed through the turbine.

This is the explanation of a hydro-electric power plant in a detailed way. 

Other Aspects related to Turbines:

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