The Kaplan Turbine: Components, Working Principles, Advantages, and Applications

Working of Kaplan Turbine:

The water is poured into the scroll casing before the penstock. The scroll casing is made in such a way that the flow pressure is not lost. The cross-section of the scroll casing decreases evenly to maintain water pressure.

Then with scroll casing, the guide vanes transport the water to the runner. In cranial turbines, guide vans are adjustable and can be adjusted to meet the required flow rate.

If the guide vanes were not present, the flow in nature would be greatly increased due to its tangent penetration and would reduce the performance of the turbine, so the guide vanes also control the vortex of the water flow.

When the guided van carries water directly towards the runner, the water enters the main area where it meets the runner blade. Runner blades are adjustable in cranial turbines to maintain optimal angles of attack with varying flow rates.

When the velocity of the flow rate water after leaving the runner blade is higher, i.e., The relative velocity is more axial, so the runner blade must be adjusted vertically for the optimal angle of attack.

Similarly, when the flow rate is low, the relative velocity is more tangent, and the runner blade must pitch tangentially.

From the runner blades, water enters the draft tube, where the kinetic and pressure energy of the turbine decreases. Kinetic energy is converted into pressure energy, which leads to increased water pressure and finally water discharge from the turbine through the tri race.

The runner rotates the rotation shaft of the blade to which the runner blades are attached. This rotation of the shaft is used for power generation.

What Is a Kaplan Turbine?

The Kaplan turbine is a propeller-type, axial flow water turbine. It has adjustable blades. Adjustable blades help achieve good efficiency in a wide range of heads and are available for turbines.

It is suitable for low head & high flow applications. This is a development of the Francis turbine. It is designed to operate where the head is lower, unlike the Francis turbine, where it is not possible.

Main Parts of Kaplan Turbine:

It is a spiral type of casing reducing the cross-section area. From the penstock, the water enters the scroll cover and then into the guide van, where the water passes 90 ° and flows axially through the runner.

This protects the runner, runner blade guide van, and other internal parts of the turbine from external damage.

#2. Guide Vane Mechanism-

It is the only controlled part of the entire turbine, which opens and closes depending on the demand for electricity required.

In the case of greater power generation requirements, it opens wider to allow more water to hit the rotor blades, and when the low power output is required, it closes itself to stop the flow of water does. If the guide vanes are absent, then the turbine may not work efficiently, and its efficiency decreases.

#3. Draft Tube-

The exit pressure of the runner of the reaction turbine is generally less than the atmospheric pressure. Exit water cannot be drained directly from the tailrace. A tube or pipe of a slowly growing area is used to discharge water from the exit of the turbine to the tailrace.

This tube of growing area is called a draft tube. One end of the tubes is connected to the runner’s outlet while the other end merges below the water level in the tail-race.

#4. Runner Blades-

The heart of the component in the cranial turbine is its runner blades, as it is the rotating part that helps in the production of electricity. the shaft is connected to the shaft of the generator.

The runner of this turbine has a large boss with its blades mounted, and the blades of the runner are adjustable to an optimum angle of attack for maximum power output. the Kaplan turbine has a twist along its length.

Advantages of the Kaplan Turbine:

The advantages of the Kaplan turbines are listed below:-

1. The effectiveness curve of cranial turbine residues is flat for the full load range.
2. It is extra dense in construction and smaller in size for equal strength development.
3. Its component load working capacity is very high.
4. Easy to build with less space required.
5. Fatal defects of the heel are eliminated.

Disadvantages of Kaplan Turbine:

However, Kaplan turbines have some drawbacks, and they are:

1. There is a possibility of the cavity due to the high-velocity flow of water.
2. Lack of water is a source of danger in the generator chamber with a shortage.
3. The very large flow rate of the Kaplan turbine is required.
4. Kaplan turbine requires a heavy-duty generator.
5. Maintenance costs are very high.

Applications of Kaplan Turbine:

Here are some applications of Kaplan turbines:-

1. Kaplan turbines are widely used all over the world for power generation.
2. They cover the lowest head hydro sites & are particularly suited to high flow conditions.
3. Inexpensive microturbines are manufactured for individual power generation, with heads two feet short.
4. Large Kaplan turbines are individually designed to operate at the highest possible efficiency for each site, typically over 90%.
5. They are very expensive to design, manufacture, & install but work for decades.

In today’s lesson, we learned what the parts of the Kaplan turbine, their functions and advantages, disadvantages, and applications of the Kaplan turbine are.

Frequently Asked Questions (FAQ) about Kaplan Turbines

What is a Kaplan Turbine?

A Kaplan turbine is a propeller-type, axial flow water turbine with adjustable blades designed for low head and high flow applications. It is a development of the Francis turbine, tailored for operations where lower head conditions exist.

How does a Kaplan Turbine work?

Water enters the scroll casing, which maintains pressure, then passes through guide vanes that control the flow and vortex. The water then reaches the runner blades, which adjust their angle to optimize performance. Finally, water exits through a draft tube, converting kinetic energy to pressure energy, and the rotation of the runner generates electricity.

What are the main components of a Kaplan Turbine?

The main components include:

1. Scroll Casing: Directs water into the turbine while maintaining pressure.
2. Guide Vane Mechanism: Controls water flow and direction.
3. Draft Tube: Discharges water while converting kinetic energy to pressure energy.
4. Runner Blades: Adjustable blades that convert water flow into rotational energy.

What are the advantages of using a Kaplan Turbine?

1. High efficiency over a wide range of flow conditions.
2. Compact and smaller size for equivalent power output.
3. High load-carrying capacity of components.
4. Space-efficient and easier to construct.
5. Eliminates fatal defects associated with heel design.

What are the disadvantages of Kaplan Turbines?

1. Potential for cavitation due to high water flow velocity.
2. Risk of water shortage in the generator chamber.
3. Requires a very high flow rate.
4. Needs a heavy-duty generator.
5. High maintenance costs.

What are the typical applications of Kaplan Turbines?

1. Widely used for power generation globally.
2. Suitable for low head hydro sites with high flow conditions.
3. Utilized in microturbines for individual power generation.
4. Large Kaplan turbines are custom-designed for optimal efficiency at specific sites.
5. Despite high design and installation costs, they offer long-term operational efficiency.

How do guide vanes affect the performance of a Kaplan Turbine?

Guide vanes control the flow rate and direction of water entering the runner blades, ensuring optimal performance by reducing turbulence and vortex formation. Adjustable guide vanes allow the turbine to adapt to varying flow conditions, maintaining high efficiency.

What is the role of the draft tube in a Kaplan Turbine?

The draft tube discharges water from the turbine while converting kinetic energy to pressure energy, thereby increasing the pressure and facilitating efficient water exit from the turbine to the tailrace.

How do adjustable runner blades enhance the efficiency of a Kaplan Turbine?

Adjustable runner blades can change their pitch to maintain the optimal angle of attack depending on the flow rate. This adaptability ensures maximum power output and efficiency under varying operational conditions.

Why is the Kaplan Turbine suitable for low head applications?

The Kaplan turbine is designed to operate efficiently at low head conditions where other turbines like the Francis turbine are less effective. Its adjustable blades and axial flow design make it ideal for environments with low water heights but high flow rates.

What maintenance considerations are there for Kaplan Turbines?

While Kaplan turbines are highly efficient, they require regular maintenance due to potential issues like cavitation and the need for heavy-duty generators. Proper upkeep ensures long-term functionality and efficiency.