Kaplan Turbine

A Kaplan turbine is basically a propeller with adjustable blades inside a tube. It is an axial-flow turbine, which means that the flow direction does not change as it crosses the rotor.

1. Scroll Casing

It is a spiral type of casing that has decreasing cross section area. The water first enters into the scroll casing and then it moves through it to the guide vanes and finally to the runner blades. It protects the runner, runner blades guide vanes and other internal parts of the turbine from an external damage.

2. Guide Vanes and Guide Mechanism

Guide vanes are used to direct the water to the runner blades smoothly by decreasing its swirl velocity. If guide vanes is absent than the turbine can not work efficiently and its efficiency decreases. The guides are adjustable in Kaplan turbine. Its opening and closing depends upon the demand of power requirement. In case of more power output requirements, it opens wider to allow more water to hit the blades of the rotor and when low power output requires it closes itself to cease the flow of water.

3. Runner and Runner Blades

Runner is the rotating part of the turbine or we can say that it is the heart of the Kaplan turbine. Its shaft is connected to the shaft of the generator. The runner of the this turbine has a large boss on which its blades are attached and the the blades of the  runner is adjustable to an optimum angle of attack for maximum power output. The blades of the Kaplan turbine has twist along its length.

Draft Tube

It is a tube which is used to increases the pressure of the fluid or water that exits the turbine. It has increasing cross section area. Draft tube is used only in reaction turbine. It increases the pressure of the water that leaves the runner blades. Since the water at exit of the turbine has very low pressure and if its pressure is not increased than the back flow of the tail race water takes which can damage the turbine. So to increase the pressure of the exiting water we uses draft tube. It converts the kinetic energy of the water into pressure energy as it passes through draft tube and the pressure of the water increases. The draft tube has to increases the pressure of the water upto such an extent that it must always greater than the pressure of tail race water and prevents the back flow of water from the tail race to the turbine. If it does not happens than cavitation may results and causes damage to the turbine.