Francis Turbine: Parts, Working, Advantages, Disadvantages & Applications

Published: 20 Dec 2025

In this article, we will learn about the Francis Turbine, its main parts and their functions, how it works, its advantages and disadvantages, and where it is used. By reading this article, you will understand how these turbines generate electricity and why they are so commonly used in hydropower plants.

What is Francis Turbine?

The Francis turbine is a reaction-based hydro turbine that uses a combination of radial and axial water flow. Water flows radially into the turbine and exits axially, making it a mixed-flow turbine. When high-pressure water enters the turbine, it hits the blades and makes the runners spin. This spinning motion creates mechanical power, which later turns into electricity. Developed by James B. Francis, it is widely used in medium- and large-scale hydroelectric power plants for efficient electricity generation.

Construction or Main Components of Francis Turbine

Here are the main parts and their simple functions:

1. Spiral Casing

The spiral casing, also called a scroll case or volute, is a curved inlet pipe that surrounds the turbine runner. It directs water evenly towards the guide vanes and maintains uniform velocity along the circumference. The cross-sectional area of the casing gradually decreases to maintain pressure and energy efficiency.

2. Stay Vanes

Stay vanes are fixed vanes placed before the guide vanes. They support the structure and guide water flow toward the runner. Their main role is to reduce swirling and make the water flow more linearly, improving the turbine’s efficiency.

3. Guide Vanes

Guide vanes, also called wicket gates, are adjustable vanes that control the angle and flow of water entering the runner. They help regulate the turbine’s power output according to load and optimize the impact of water on the runner blades.

4. Runner Blades

The runner blades are the core part of the turbine. Water strikes these blades and causes the runner to rotate, producing mechanical energy. The runner blades are divided into two parts:

Lower part: Uses the impulse force of water to rotate.

Upper part: Uses the reaction force of water to continue rotation.

5. Draft Tube

The draft tube is a gradually expanding tube connected to the runner’s outlet. Its main function is to reduce water velocity and recover energy before water exits the tailrace. This increases overall turbine efficiency.

6. Penstock

The penstock is the main water inlet pipe that conveys water from the dam or reservoir to the turbine. It is designed to handle high pressure and ensure that water reaches the turbine smoothly.

7. Governing Mechanism

The governing mechanism controls the movement of the guide vanes according to load requirements. Adjusting the water flow into the turbine ensures stable power output and prevents overloading.

Francis Turbine Working Principle

The Francis turbine works on the reaction principle, meaning water pressure and flow both act on the blades to rotate the runner. The Francis turbine transfers energy gradually from the inlet to the outlet.

Water enters the turbine at high pressure through the penstock and spiral casing, flows through stay vanes and guide vanes, and strikes the runner blades. The blades rotate due to reaction and impulse forces, and the water exits through the draft tube, where the remaining energy is recovered.

Working of Francis Turbine

The Francis turbine operates as a mixed-flow reaction turbine, efficiently converting the kinetic and potential energy of water into mechanical energy. Here’s a step-by-step explanation of how it works.

Water enters the spiral casing from the penstock, carrying high pressure from the reservoir or dam.
Stay vanes and wicket gates guide the water at the optimal angle to strike the runner blades, ensuring smooth energy transfer.
The water then enters the runner in a radial direction, moving from the outer edge toward the center.
Runner blades rotate as water exerts force on them, turning the turbine shaft. The design of the blades allows the turbine to harness both impulse and reaction forces from water.
Water exits the runner in an axial direction, flowing into the draft tube.
The draft tube slows down the water, recovering the remaining kinetic energy and minimizing energy loss.
The rotating shaft drives a generator, producing electricity that can be supplied to the grid.

Applications of Francis Turbine

Francis turbines are used in many places, such as:

Medium-head hydropower plants
Large power stations
Water dams
Pumped storage plants
Renewable energy projects

They are very common because they work well in many water conditions.

Advantages of Francis Turbine

Here are the main benefits:

Works with medium pressure and medium flow.
Gives high efficiency.
Runs smoothly for long hours.
Has low maintenance needs.
Suitable for large power generation.

Disadvantages of Francis Turbine

Some drawbacks include:

Not good for very low or very high water heads.
Needs careful installation.
Can get damaged by dirty water.
Costs more than simple turbines.

Conclusion

In conclusion, in this article, we covered what a Francis Turbine is, its parts and their functions, working principle, operation, advantages, disadvantages, and applications in detail. We hope you have learned something useful about this widely used and highly efficient hydroelectric turbine.