In this article we will learn about the main types of hydro turbines. We will discuss about mainly three types of turbines which description is given below.
Types of hydro turbines
There are basically three types of hydro turbines which are as follows
1. Peloton turbine
Peloton turbine works under large head and low quantity of water. The potential energy of water in the pen stock is converted into kinetic energy in a jet of water issuing from a nozzle. The pressure inside is atmospheric pressure. The water jet impinges on buckets fixed on the periphery of rotor and causes the motion of the rotor. After performing work. Water discharges into the tail race.
Each bucket is divided into two hemispherical cups with a ridge in the center. The ridge divides the jet into two symmetrical parts. The axial thrust produced in the two parts of the buckets cancel out each other. The rate of water flow can be controlled by the movement of spear.
Most of the peloton turbines have one jet through machines with two or four jets are also used. The rotor or runner is made of cast steel. Bucket is made of cast iron, bronze or stainless steel. The bucket is bolted on to the runner but integral casting of buckets with runner is also possible. Peloton turbines have usually horizontal alignment. These are special types of hydro turbines.
2. Francis turbine
A reaction turbine develops power partly due to the velocity of water and partly due to the difference in pressure acting on the front and back of the runner buckets. A Francis turbine is a reaction turbine suitable for medium head and medium flows. They are built in large sizes and are generally of vertical type to effect economy in space. The alternator is mounted above the turbine and is thus free from flooding.
A modern francs turbine is an inward mixed flow reaction turbine. The water, under pressure, enters the runner from guide vanes radially and discharges out of the runner axially. The motion of water is controlled by movable inlet wicket gates, fixed around the runner, through which the water passes on its way from the spiral casing to the runner, since the pressure at inlet is more than that at out let, the water flows in a closed circuit and the runner is always full of water. After doing work, water is discharged to the tail race through a closed tube known as draft tube which has a gradually enlarging section. The free end of the draft tub is submerged deep in tail race water. The draft tube enables the machine to be placed above the tail race without loss of head between the runner and the tail race. As in all reactions turbines, cavitation is a serious problem in a Francis turbine.it is also special types of turbines . for knowing more about Francis turbine you must watch this video.
3.. Kaplan propeller turbine
propeller turbine is reaction turbine suitable for low head and large quantity of water. It is suitable for heads beldo 30m. a Kaplan turbine is a propeller turbine with adjustable blades being that a Kaplan turbine operates at high efficiency even under part load conditions. Their specific speeds vary from 300 to 1000 or even higher.
All parts of Kaplan turbine such as spiral casing, guide mechanism and draft tube except runner are similar to those of a Francis turbine. A Kaplan runner has only three to six blades as compared to 16-24 for a Francis runner. The smaller number of blades causes a reduction in contact surface and hence in frictional resistance. Further.in Kaplan turbine eater strikes the blades axially.. It is high speed types of hydro turbines.
The speed of Kaplan turbines is more than that of Francis turbines and lies in the range of 400-1500 rpm, the high speed resulting in lower cost of runner and alternator and cheaper power house structure. A Kaplan turbine has a vertical configuration. A Kaplan runner is also capable of reverse operation as a pump and is ideally suitable for pumped storage scheme. The cavitation problem in Kaplan turbines is more serious than in Francis turbines. It is special types of hydro turbine which speed is higher than other types of hydro turbines
Hence it is the main types of turbines if you will find any incorrect in above article you must comment below in comment box.
Here also a video of kaplan turbine working and application.