Hydraulic Turbines

Turbine:

Turbine is rotating mechanical device which converts the one form of the energy into another form.

Types of turbines:

• Hydraulic turbines
• Stream turbines
• Gas turbines
• Wind turbines etc...

Hydraulic turbines:

Hydraulic turbine is the device which converts the hydraulic energy into mechanical energy (i.e. hydraulic energy is obtain from the moving water) and the turbine which is coupled to the generator then the generator gets the mechanical energy and it converts the mechanical energy into electrical energy this process is known as hydro electric power.

Types of Hydraulic turbines:

According to the type of energy at inlet

Impulse turbine:

The energy available at the inlet of the turbine runner is only kinetic energy and water casing is not necessary for the runner

Example: pelton wheel

Reaction turbine:

The energy available at inlet of the turbine runner is both kinetic energy and pressure energy and water casing is must necessary to the runner of the turbine.

Example: Francis turbine, Kaplan turbine

Pelton wheel:

It is the turbine which converts the hydraulic energy into mechanical energy. Pelton wheel is the impulse type turbine because of the energy of available at the inlet is only kinetic energy.

The runner of the pelton wheel consists of a circular disc with a number of buckets evenly spaced on its periphery. The buckets have a shape of double semi-ellipsoidal cups each bucket is divided into two parts by a sharp vertical edge is known as splitter.

The water is taken to the turbine from the reservoir by using of pen stocks. A nozzle is fitted on end of the pen stock which converts the hydraulic energy in to kinetic energy and the nozzle is provided with a spear for controls the water striking to the runner and the spear is operated by a hand wheel if the spear changes the opening in the nozzle by moving in or out.

The jet of water from the nozzle strikes the buckets of the pelton wheel then in the direction tangential to the wheel and wheel starts rotating on the shaft and the shaft is coupled to generator. The water coming out the wheel is discharges into tail trace and casing is made up of the cast iron is usually provided for a pelton wheel to prevent splashing of water and to discharges to the tail trace.

The small brake nozzle is provided which directs the water jet on the back of the buckets. It causes braking action of the wheel.

Applications of pelton wheel turbine:

• High head water level
• Low discharge of water

Francis turbine:

Francis turbine which is mixed flow type reaction turbine.tn this turbine water enters to the runner radially at its over periphery and leaves axially at its center and inlet of the turbine is posses the both kinetic energy and pressure energy.

Main parts of the Francis turbine:

The following parts are present in the turbine they are

1. Scroll casing
2. Guide mechanism
3. Runner
4. Draft tube

Scroll casing:

The water from the penstock enter into scroll casing. It is completely surrounds the runner and guide mechanism. The purpose of the casing is to keep the velocity of water completely constant. It is made up of the cast steel or plate steel.

Guide mechanism:

Guide mechanism is consists of a stationary circular wheel all rounded on the runner of the turbine. The guide vanes are fixed on it. The water coming out of the scroll casing is passes through the guide vanes and rotated about its pivot center.

Runner:

It consists of the series of curved vanes which are fitted between two circular plates. The vanes are so shaped that water enters the runner radially at the outer periphery and leaves axially at the inner periphery.

It is made up of cast steel, cast iron (or) stainless steel. The runner is mounted on the shaft.

Draft tube:

A draft tube is a pipe which increases in area gradually it discharges water from the outlet of reaction turbine to the tail trace.

Types of draft tubes:

There are four types of draft tubes,

They are:

• Straight divergent tube
• Moody spreading tube
• Simple elbow tube
• Elbow tube

Kaplan turbine:

Kaplan turbine is developed by the V.Kaplan (1876-1934) by its known as the Kaplan turbine.

Kaplan turbine is an axially flow reaction turbine which works at low head and high discharge water

The main components of the Kaplan turbine are:

• Scroll casing
• Runner vanes
• Guide vanes
• Draft tube
• Hub etc...

The water from the nozzle which enters in it between the Guide vanes and Runner vanes and turns through 90^o

Runner consists of 4 blades are attached to the hub and shaped of blades are made so far flow axially through runner.

Difference between the pelton wheel, Francis turbine, Kaplan turbine: