35100KW Power Hydro Electric 41m Small Francis Turbine

Francis Turbine Generator Power Hydro Electric Generator For Power Plan

Francis turbine is a kind of turbine suit to water head 20-300meters and with certain suitable flow.
It could be divided into vertical and horizontal arrangement. Francis turbine have the advantage of high efficiency, small size and reliable structure.

The piece, shaped like a snail shell, is generally made of metal material and has a circular cross section. The seat ring is placed between the volute and the guide vane, and is composed of an upper ring, a lower ring, and a number of upright posts, which are directly connected to the volute; the upright post is wing-shaped and cannot be rotated. It is also called a fixed guide vane. The water guide mechanism is composed of movable guide vane, speed control ring, boom, connecting rod and other components. The runner is directly connected to the main shaft (see the main shaft of the turbine) and is the rotating part of this type of turbine. The runner is composed of an upper crown, a lower ring, a drain cone and a number of fixed blades. Its shape and the matching dimensions of each component are based on its The head used varies. The draft tube is the discharge part of the turbine that directs the water flow from the runner outlet to the downstream. It is generally elbow-shaped. Small-sized turbines often use straight tapered draft tubes.

Francis Turbine Components

1. Spiral Casing
Spiral casing is the inlet medium of water to the turbine. The water flowing from the reservoir or dam is made to pass through this pipe with high pressure. The blades of the turbines are circularly placed, which mean the water striking the turbines blades should flow in the circular axis for efficient striking. So the spiral casing is used, but due to circular movement of the water, it looses its pressure.

2. Stay Vanes
Stay vanes and guide vanes guides the water to the runner blades. Stay vanes remain stationary at their position and reduces the swirling of water due to radial flow, as it enters the runner blades. Thus making turbine more efficient.

3. Guide Vanes
Guide vanes are not stationary, they change their angle as per the requirement to control the angle of striking of water to turbine blades to increase the efficiency. They also regulate the flow rate of water into the runner blades thus controlling the power output of a turbine according to the load on the turbine

4. Runner Blades
The performance and efficiency of the turbine is dependent on the design of the runner blades. In a Francis turbine, runner blades are divided into 2 parts. The lower half is made in the shape of small bucket so that it uses the impulse action of water to rotate the turbine.

The upper part of the blades use the reaction force of water flowing through it. These two forces together makes the runner to rotate.

5. Draft Tube
The pressure at the exit of the runner of Reaction Turbine is generally less than atmospheric pressure. The water at exit cannot be directly discharged to the tail race. A tube or pipe of gradually increasing area is used for discharging water from the exit of turbine to the tail race.

This tube of increasing area is called Draft Tube. One end of the tube is connected to the outlet of runner while the other end is sub-merged below the level of water in the tail-race.

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