Short Answer:

A Kaplan turbine is a type of reaction turbine that works efficiently under low-head and high-flow conditions. It was invented by Viktor Kaplan in 1913. The turbine has adjustable blades and guide vanes, allowing it to maintain high efficiency even when the water flow changes. It is widely used in hydroelectric power plants where large quantities of water are available at low heads.

The Kaplan turbine is an axial-flow turbine, meaning water flows parallel to the turbine shaft. It is similar in design to a ship’s propeller, and because of its adjustable runner blades, it can operate effectively under varying load conditions, making it very efficient and reliable for low-head applications.

Detailed Explanation :

Kaplan Turbine

A Kaplan turbine is a reaction turbine of the axial flow type that is mainly used in hydroelectric power stations operating under low head (less than 70 meters) and high discharge conditions. It was developed by the Austrian engineer Viktor Kaplan in 1913. The unique feature of the Kaplan turbine is its adjustable runner blades and guide vanes, which automatically adjust their angle depending on the flow rate. This feature allows the turbine to maintain high efficiency (up to 95%) over a wide range of flow conditions.

It is an axial-flow turbine, meaning the water flows parallel to the axis of rotation of the turbine. The Kaplan turbine is suitable for sites where a large volume of water is available, such as low-head dams and run-of-the-river hydroelectric plants. It is a modified version of the Francis turbine designed to perform well under low head and high discharge.

Construction of Kaplan Turbine

The main components of a Kaplan turbine are:

1. Scroll Casing (Spiral Casing):
   The scroll casing is designed to distribute the water evenly around the guide vanes. It surrounds the runner completely and has a gradually decreasing cross-section to maintain uniform velocity of water as it flows around.
2. Guide Vanes (Wicket Gates):
   The guide vanes regulate the flow of water entering the runner. These vanes can be adjusted to control the flow rate and direction of the water striking the runner blades, thus controlling the power output of the turbine.
3. Runner and Blades:
   The runner of the Kaplan turbine consists of 3 to 6 adjustable blades mounted on a hub. The blades can be rotated or twisted automatically with the help of a hydraulic mechanism. This adjustment ensures that the angle of attack of water remains optimal under all load conditions, resulting in maximum efficiency.
4. Draft Tube:
   The draft tube is fitted at the exit of the runner. It gradually increases in cross-section to convert the kinetic energy of the water leaving the runner into pressure energy, minimizing energy losses. It also allows the turbine to be placed above the tailrace level without reducing efficiency.
5. Shaft and Bearings:
   The main shaft connects the runner to the electric generator. Bearings are provided to support the shaft and reduce friction during operation. The shaft transmits mechanical energy from the runner to the generator to produce electricity.

Working Principle of Kaplan Turbine

The Kaplan turbine works on the principle of reaction. Water from the dam or reservoir is brought to the turbine through the penstock. The water enters the scroll casing, which directs it to the guide vanes. The guide vanes control the flow and direction of water so that it enters the runner blades at an appropriate angle.

As the water flows through the adjustable runner blades, both pressure and velocity change, generating a reaction force on the blades. This reaction force causes the runner to rotate. The rotation of the runner turns the shaft, which is connected to an electrical generator. The generator then converts the mechanical energy of rotation into electrical energy.

The water finally passes through the draft tube and is discharged into the tailrace with minimum energy loss. The draft tube helps in recovering part of the kinetic energy of the water leaving the runner, thus improving the overall efficiency of the turbine.

The special feature of the Kaplan turbine is the adjustable runner blades, which automatically change their pitch according to the load and flow conditions. This makes it highly efficient for variable water flow rates, unlike fixed-blade turbines.

Advantages of Kaplan Turbine

1. High efficiency over a wide range of load and flow conditions.
2. Suitable for low-head and high-flow applications.
3. Adjustable blades provide better control of power output.
4. Compact design and easy installation in low-head dams.
5. Simple operation and high reliability.

Applications of Kaplan Turbine

Kaplan turbines are widely used in low-head hydroelectric power plants, such as river-based or run-of-the-river stations. They are commonly installed in large dams where water flow is abundant but the available head is small. Examples include power stations on large rivers like the Rhine, Mississippi, and Ganga.

They are ideal for heads between 2 to 70 meters and discharges ranging from 10 to 700 cubic meters per second. Their adjustable blade design allows them to handle variable flow efficiently, making them the preferred choice for low-head energy conversion.

Conclusion

In conclusion, the Kaplan turbine is an advanced reaction turbine that efficiently converts hydraulic energy into mechanical energy in low-head, high-flow water conditions. Its adjustable blades and guide vanes make it one of the most efficient turbines in hydroelectric power generation. Because of its adaptability, compact design, and high performance, the Kaplan turbine is extensively used in modern hydroelectric power plants across the world, playing a vital role in sustainable energy production.