The Francis turbine is a hydraulic turbine used in hydropower installations with a considerable height of fall.
The Francis turbine is a type of hydraulic turbine built by British-American engineer James Bicheno Francis. The function of the Francis turbine is mainly to generate electricity with the help of a generator. Francis turbines have a high utilization capacity of more than 90% and a wide range of activities compared to the height (building drop) of the fluid flowing through the turbine. This is particularly emphasized in water where it achieves optimum performance in a building drop of 20 meters to 700 meters and the output power varies from a couple of kilowatts to 750 MW. The diameter of the rotor can be from 1 to 10 m and the speed of rotation is from 83 to 1000 rpm.
The Francis turbine is the most common type of turbine that is installed in power generation plants that operate on the basis of the mass flow of water through a production plant. In most cases, these are renewable energy plants of hydroelectric origin.
Uses of the Francis turbine
Francis turbines have the characteristic that they have a high efficiency. In addition, this type of hydraulic turbines can be designed with a varied range of heads and flows.
Currently, the Francis turbine is one of the most used turbines worldwide. The Francis type units cover a head range of 40 to 600 m (130 to 2,000 feet), and the power output of their connected generator varies from a few kilowatts to 800 MW. The large Francis turbines are individually designed so that each site works with the water supply and the water height given to the highest possible efficiency. Generally, Francis turbines work with an efficiency of more than 90%.
In contrast to the Pelton turbine, the Francis turbine runs at its best completely filled with water at all times. The turbine and outlet channel can be placed lower than the level of the lake or the sea on the outside, which reduces the tendency to cavitation.
In addition to the production of electric power, the Francis trucks can also be used for pumping storage. In this case, a tank is filled by the turbine that performs the function of pump driven by the generator. The generator, in this case, acts as a large electric motor during periods of low energy demand. When the demand for energy is high, the generator is inverted and used to generate energy during peak demand. These pump storage tanks act as large sources of energy storage to store "excess" electrical energy in the form of water in high deposits. This is one of the few methods that allow storing a temporary excess of electrical capacity for later use.
Theory of the hydraulic turbine Francis
The Francis turbine, which is a kind of water jet turbine, uses the kinetic energy of tap water as pressure energy to spin a waterwheel.
The turbine is located between the intake port where the high pressure is applied and the low pressure discharge port part, and it is usually installed at the base of the dam of a hydroelectric power station.
The entrance part of the turbine is a casing (spiral chamber) formed in spiral form, and several guide vanes (guide vanes) cause the water to flow tangentially towards the corridor. Flowing sheet of water, to rotate the corridors. The opening degree of the guide fin can be adjusted to perform an efficient operation according to the amount of water used.
The water that passes through the corridor also acts on the corridor when it goes towards the axial center. In addition to water pressure (water pressure), this property supports the use of hydropower from the water that flows inland.
After acting on the corridor in the form of a coffee cup, the water comes out with the kinetic energy and with the potential energy minimized and the vortex also disappears. At the outlet of the hydraulic turbine, a suction tube formed in connection with the reduction of the water velocity and the restoration of the kinetic energy is connected.
History of the Francis turbine
Historically, many types of turbines have been used in mills and factories, but most of them have problems with efficiency. In the 19th century, the improvement of the hydraulic turbine advanced and, finally, the shoulder was aligned with the steam engine as the main engine.
In 1826, the French engineer Benoit Fourneyron developed the first water turbine, which had a high degree of utilization (up to 80%). In the Fourneyron water turbine, water flows through the stator blades, from the shaft to the periphery and the impact on the rotor blades, by converting the potential energy of the water into kinetic energy.
In 1848 the American engineer J.B. Francis introduced a revolution in the design of a hydraulic turbine with the construction of a reaction turbine. Reaction or compression turbines are called water turbines, where the pressure at the rotor inlet is greater than at the outlet. In pretreatment turbines, part of the potential energy is converted into kinetic energy in the stator and part in the rotor. Turning the stopcock causes a change in the amount of movement and reactive force (pressure difference, Coriolis effect, etc.)