CLASSIFICATION OF TURBINES

Hydraulic machinery

•Turbine is a device that extracts energy from a fluid (converts the energy held by the fluid to mechanical energy)
•Pumps are devices that add energy to the fluid (e.g. pumps, fans, blowers and compressors).

Turbines

•Hydro electric power is the most remarkable development pertaining to the exploitation of water resources throughout the world.
•Hydroelectric power is developed by hydraulic turbines which are hydraulic machines.
•Turbines convert hydraulic energy or hydro-potential into mechanical energy.
•Mechanical energy developed by turbines is used to run electric generators coupled to the shaft of turbines.
•Hydro electric power is the most cheapest source of power generation.
•J.V. Poncelet first introduced the idea of the development of mechanical energy through hydraulic energy.

Modern hydraulic turbines have been developed by L.A. Pelton (impulse), G. Coriolis and J.B. Francis (reaction) and V Kaplan (propeller)

Types of turbines

•Head and quantity of water available
•Hydraulic action of water
•Direction of flow of water in the runner

•Specific speed of turbines
•Disposition of the shaft of the runner

Turbines can be classified on the basis of:

•Based on head and quantity of water

According to head and quantity of water available, the turbines can be classified into

a) High head turbines

b) Medium head turbines

c) Low head turbines

a) High head turbines

High head turbines are the turbines which work under heads more than 250m. The quantity of water needed in case of high head turbines is usually small. The Pelton turbines are the usual choice for high heads.

b) Medium head turbines

The turbines that work under a head of 45m to 250m are called medium head turbines. It requires medium flow of water. Francis turbines are used for medium heads.

c) Low head turbines

Turbines which work under a head of less than 45m are called low head turbines. Owing to low head, large quantity of water is required. Kaplan turbines are used for low heads.

•Based on hydraulic action of water

According to hydraulic action of water, turbines can be classified into

a) Impulse turbines
b) Reaction turbines

a) Impulse turbines

If the runner of a turbine rotates by the impact or impulse action of water, it is an impulse turbine.

b) Reaction turbines

These turbines work due to reaction of the pressure difference between the inlet and the outlet of the runner.

•Direction of flow of water in the runner

Depending upon the direction of flow through runner, following types of turbines are there

a) Tangential flow turbines

b) Radial flow turbines

c) Axial flow turbines

d) Mixed flow turbines

a) Tangential flow turbines

When the flow is tangential to the wheel circle, it is a tangential flow turbine. A Pelton turbine is a Tangential flow turbine.

b) Radial flow turbines

In a radial flow, the path of the flow of water remains in the radial direction and in a plane normal to the runner shaft. No pure radial flow turbine is in use these days.

c) Axial flow turbines

When the path of flow water remains parallel to the axis of the shaft, it is an axial flow turbine. The Kaplan turbine is axial flow turbine

d) Mixed flow turbines

When there is gradual change of flow from radial to axial in the runner, the flow is called mixed flow. The Francis turbine is a mixed flow turbine.

•Based on specific speed of turbine

Specific speed of a turbine is defined as the speed of a geometrically similar turbine which produces a unit power when working under a unit head.

The specific speed of Pelton turbine ranges between 8-30, Francis turbines have specific speed between 50-250, Specific speed of Kaplan lies between 250-850.

•Based on disposition of shaft of runner

Usually, Pelton turbines are setup with horizontal shafts, where as other types have vertical shafts.