Short Answer:

A Kaplan turbine is an axial flow reaction turbine designed to generate electricity from low-head and high-discharge water sources. It was developed by Viktor Kaplan in 1913. The turbine has adjustable blades and guide vanes that help maintain high efficiency even when the water flow or load changes.

In a Kaplan turbine, water flows parallel to the turbine shaft (axial direction) and passes through adjustable runner blades. It is ideal for low-head (2–40 meters) and high-flow rivers. Because of its flexibility and high efficiency, the Kaplan turbine is widely used in modern hydroelectric power plants.

Detailed Explanation :

Kaplan Turbine

The Kaplan turbine is a type of reaction turbine that works on the principle of converting both the pressure energy and kinetic energy of water into mechanical energy. It is an axial flow turbine, meaning that the water enters and leaves the runner in a direction parallel to the turbine shaft.

It was invented by Viktor Kaplan, an Austrian engineer, in 1913. The Kaplan turbine is often described as a propeller-type turbine with adjustable blades. The special feature of this turbine is that both the runner blades and guide vanes can be adjusted automatically according to the flow of water, ensuring maximum efficiency under varying load conditions.

The Kaplan turbine is best suited for low-head (2 to 40 meters) and high-discharge (large flow) conditions, such as in rivers or canals with relatively slow-moving water. It is one of the most efficient turbines ever developed for such conditions, with efficiency levels of 85–90%.

Construction of Kaplan Turbine

The Kaplan turbine consists of several important parts that work together to convert water energy into mechanical energy efficiently.

Scroll Casing (Spiral Casing):
The scroll casing is a spiral-shaped housing that distributes water uniformly around the runner. It gradually decreases in cross-section area to maintain constant velocity as the water moves toward the guide vanes.
Guide Vanes or Stay Vanes:
These vanes are placed inside the casing and control the amount and angle of water flowing to the runner blades. The guide vanes can be adjusted according to load conditions, ensuring that the water enters the runner at the correct angle for maximum efficiency.
Runner and Blades:
The runner is the rotating part of the turbine, which consists of three to six adjustable blades attached to a central hub. The blades act like those of a ship’s propeller. Water flows through the runner axially and exerts force on the blades, causing the runner to rotate. The angle of the blades can be changed automatically depending on the water flow, maintaining high efficiency under variable loads.
Draft Tube:
The draft tube is a gradually expanding tube fitted at the exit of the runner. It converts the kinetic energy of water leaving the runner into pressure energy and directs the water into the tailrace. The draft tube helps recover some of the energy lost during flow and allows the turbine to be placed above the tailrace without loss of efficiency.
Shaft and Bearings:
The runner is connected to a shaft supported by bearings. The shaft transfers mechanical energy to the generator, which then converts it into electrical energy.
Generator:
The generator is coupled with the turbine shaft and converts the mechanical rotation into electrical power. The whole assembly is usually housed inside a powerhouse.

Working of Kaplan Turbine

The working principle of the Kaplan turbine is based on the reaction principle, where energy is generated by the combined action of pressure and velocity changes of the water.

The working process can be described in steps as follows:

Water Flow from Reservoir:
Water from the reservoir or dam is carried to the turbine through a penstock (a large pipe). The water enters the scroll casing, where it is evenly distributed around the turbine.
Control by Guide Vanes:
The guide vanes adjust themselves automatically based on the water flow and power demand. They direct the flow of water at the proper angle toward the runner blades.
Flow Through Runner:
The water flows axially through the runner blades, striking them and transferring its energy. The water pressure and velocity both decrease as energy is imparted to the runner.
Rotation of Runner:
The reaction force caused by the change in direction and velocity of water makes the runner rotate. The adjustable blades of the runner automatically set themselves at the most efficient angle based on the load and flow conditions.
Energy Conversion:
The rotating runner drives the turbine shaft, which is connected to the generator. The generator converts the mechanical energy of the rotating shaft into electrical energy.
Exit Through Draft Tube:
After passing through the runner, water enters the draft tube, where its kinetic energy is partly converted into pressure energy. Finally, the water discharges into the tailrace at atmospheric pressure.

Operating Conditions

Type: Axial flow reaction turbine
Head Range: 2 to 40 meters (low head)
Discharge: High (large flow rate)
Efficiency: 85% to 90%
Direction of Flow: Axial at both entry and exit
Position: Fully submerged in water

Advantages of Kaplan Turbine

High efficiency even at varying load and flow conditions.
Adjustable runner blades and guide vanes ensure maximum performance.
Suitable for low-head and high-flow sites.
Compact design and quiet operation.
Long service life with proper maintenance.

Disadvantages of Kaplan Turbine

High initial cost due to complex design and adjustable components.
Requires precise control systems for blade and vane adjustments.
Sensitive to silt and sediment in the water, which can cause wear.
Maintenance and repair can be more complicated than simpler turbines.

Applications of Kaplan Turbine

Used in low-head hydroelectric power stations on rivers and canals.
Common in run-of-river plants, where the water flow is continuous but low in head.
Suitable for small and medium hydropower projects.
Widely used for electricity generation in flat regions or coastal areas with slow-moving rivers.

Importance of Kaplan Turbine

The Kaplan turbine is an essential part of modern hydropower systems because it provides reliable power generation even when water flow varies. The automatic adjustment of its blades and vanes makes it one of the most efficient turbines for low-head applications. Its ability to operate efficiently under partial loads helps in maximizing the use of renewable energy sources.

Conclusion :

A Kaplan turbine is an axial flow reaction turbine that converts both pressure and kinetic energy of water into mechanical energy. It is highly efficient for low-head and high-discharge conditions and operates efficiently due to its adjustable runner blades and guide vanes.

The Kaplan turbine is a key innovation in hydropower engineering, providing reliable, clean, and renewable energy from rivers and canals. Its flexible design, high performance, and suitability for varying flow rates make it one of the most effective turbines used in modern hydroelectric power generation.