Explain Francis Turbine

Explain Francis Turbine

Francis turbine:

In this article, we will learn about Francis Turbine. Francis turbine is an inward, mixed flow reaction turbine. That is, in the runner, the water flows radially and is released along its axis. It is suitable for low and medium head locations. Important parts of the Francis turbine and its structure are shown.

1. Scroll casing
2. Guide vanes or wicket gates
3. Guide wheel and governing mechanism
4. Runner blades
5. Draft tube.

1. Scroll casing:

Water from the Reservoir enters the penstock pipe through the annular space surrounding the turbine runner. As it is in spiral form, we call it spiral or scroll casing. In this casing, the direction of the flow of water decreases with its cross-sectional area.

But velocity will be steady in its path. Upon reaching the casing, the water sends out water equal to the guide blades. It is usually made of cast steel, plate steel, or concrete. The material can be selected depending on the pressure in the space used.

2. Guide vanes or wicket gates:

Guide vane is an airfoil-shaped vane designed to regulate the direction of water between the casing á runner blades. The guide vane is mounted in a fixed position (pivoted) with the regulating ring connected to the lever and links.

3. Guide wheels and governing mechanism:

The governing mechanism changes the position of the guide blades and controls the amount of water flowing into the runner to suit the load on the turbine. The regulating ring is fitted with the servomotor attached.

When loading on a turbine, the governing mechanism rotates all guide blades according to their axis. Thus the distance between the two adjacent guide vans will either increase or decrease the flow passage. This allows you to control the volume and direction of the water flowing into the runner. Guide vans can be operated by handwheel or governor.

4. Runner blades:

In the space between two rings, we call the runner blade a series of curved vans arranged in a series of orbits. Its number ranges from 16 to 24. Francis turbine is an inward mixed-flow reaction turbine that flows parallel to the axis as the water in the runner enters the radius. The runner is usually made of cast iron, cast steel, stainless steel, or bronze.

5. Draft tube:

It is a closed envelope with an increasing cross-sectional area. Its small end is attached to the runner’s exit and the other end to the tailrace. It will be airtight. This increases the efficiency of the turbine. Typically cone-shaped draft tubes are suitable for the Francis turbine.

Working:

The water from the Reservoir reaches the casing through the penstock. In Casing the water is evenly split and goes into the guide vanes. Guide vane injects water into the runner at the right angle and level. The water flowing into the runner is a high pressure and low speed. As the water passes through the guide vane, gradually the pressure energy becomes kinetic energy.

This kinetic energy is transported to the wheel and the turbine dissolves. Once the work is done inside the turbine, the water reaches the tailrace through the draft tube. The Kaplan turbine is the axial flow reaction turbine. In this, the water flows from the casing to the radius and runs parallel to the axis within the runner. Runners can also be called propeller. It is used in low pressure and high volume reservoirs. Important parts of Kaplan turbines and their structure are shown.

1. Scroll casing 2. Guide blades 3. Runner or propeller 4. Draft tube.

The main components of the Kaplan turbines are the scroll casing, the stay ring, the guide mechanism, and the draft tube, just like the Francis turbine. But the runner is just different. The runner is in the shape of a hub or boss and looks like a shallower shaft at the bottom of the shaft. 3 to 6 vane s are fitted in the Boss orbit. These runner vans have the ability to return to the desired angle of water.

Since the runner looks like a ship’s propeller, we call it a propeller turbine. There is a standard guide vane wheel around the runner. This injects water into the runner at the right angle. Guide vans are set to rotate along their axis and are connected to the guidewheel via lever and links. By operating the guide wheel, you can control the volume of water to the speed of the turbine.

Runners, guide vans, and scroll casing are located inside. Casing distributes water evenly to all guide vans. In the scroll casing, the direction of the flow of water decreases with its cross-sectional area. The runner’s exit is connected to the tailrace by the draft tube.

Working:

The water from the Reservoir reaches the casing through the penstock. It distributes water evenly to guide vans. Guide vans drive water into the runner parallel to the axis of the turbine. Now the pressure energy is converted into kinetic energy and the runner spins.

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