Short Answer:
The Francis turbine is a type of reaction turbine that works by converting both pressure energy and kinetic energy of water into mechanical energy. Water enters the turbine through a spiral casing and passes through fixed guide vanes that direct it toward moving runner blades. The pressure and velocity of water cause the runner to rotate and generate power.
This turbine operates efficiently in medium-head and high-flow water conditions. It is commonly used in hydroelectric power plants and can handle a wide range of water levels. The design allows for smooth and continuous power generation in large-scale installations.
Detailed Explanation:
Working of a Francis turbine
The Francis turbine is a popular and widely used reaction turbine in hydroelectric power generation. It is named after James B. Francis, who developed this turbine in the 19th century. The turbine works by using both the pressure energy and velocity energy of water to rotate a central runner, which is connected to a generator to produce electricity.
Water Flow Path and Energy Conversion
The working of a Francis turbine begins when water from a dam or reservoir is guided through a penstock (a large pipe) into the spiral casing of the turbine. This spiral-shaped casing distributes the water evenly around the turbine and maintains constant pressure.
The water then flows through stationary guide vanes, also called stay vanes or wicket gates. These guide vanes control the direction and speed of the water before it enters the runner blades. By adjusting the position of the guide vanes, the turbine can regulate water flow depending on power requirements.
After passing through the guide vanes, water enters the runner blades. These blades are curved and mounted on a central hub. As water flows through them, it loses both pressure and velocity, transferring energy to the blades and causing the runner to spin. Since this turbine works with water under pressure, the entire runner is submerged and enclosed in a water-tight casing to maintain proper pressure conditions.
The rotating runner is connected to a shaft, which is linked to a generator. As the runner turns, the generator also rotates, converting mechanical energy into electrical energy.
After transferring its energy, the water exits the turbine through a draft tube, which helps recover some of the kinetic energy and directs the water safely into the tailrace (the downstream channel).
Key Characteristics of Francis Turbine Working
- Works under medium head (typically 30 to 300 meters) and large water flow.
- Utilizes both pressure and velocity energy.
- Operates efficiently over a wide range of water conditions.
- Capable of regulating power output by adjusting guide vanes.
- Fully submerged runner ensures smooth operation with less vibration.
Applications
Francis turbines are mostly used in large-scale hydroelectric power stations. They are ideal for river-based projects or reservoirs where water head is moderate. They are widely adopted worldwide because of their flexibility, reliability, and high efficiency.
Conclusion:
The working of a Francis turbine involves guiding pressurized water through a spiral casing and guide vanes to curved runner blades. This process converts water’s pressure and kinetic energy into rotational motion, which is then used to generate electricity. Its efficient design and adaptability make the Francis turbine one of the most commonly used turbines in hydroelectric plants.