Francis Turbine is an impact turbine generator with simple structure, convenient manufacture and installation, reliable operation, high efficiency and low cavitation coefficient. Mixed flow-through components: volute → water guide mechanism → runner → tailpipe.
In Francis turbines, water flows into the water guiding mechanism radially through the diversion effect of the volute, which converts the kinetic energy of the liquid into static pressure energy, and then converts the static pressure energy into the kinetic energy of the rotor through the blades. The runner passes through the main shaft and the generator rotor Coupling, which drives the rotor to rotate and cut the generator stator magnetic coil, uses the principle of electromagnetic induction to generate high voltage electricity in the generator coil, and then boosts the voltage through the transformer to output the power to the power grid through the transmission line, and the water finally flows out of the runner axially.
Large and medium-sized hydraulic turbine units generally use metal volutes, whose main role is to guide the flow of fluid and convert liquid kinetic energy into static pressure energy. The inclination angle of the movable guide vane in the water guiding mechanism is adjustable. Its main function is to adjust the flow rate, switch the turbine on and off, and adjust the amount of water circulation.
Compared with the axial-flow propeller type, its structure is simpler and the highest efficiency is higher than the axial-flow type. However, when the head and load change is large, the average efficiency is lower than the axial-flow propeller type. The highest efficiency of this type of turbine Some have exceeded 95%. Francis turbines have a wide range of heads, ranging from 5 to 700 meters, but the most widely used is 40 to 300 meters.
Mixed flow runners are generally made of low-carbon steel or low-alloy steel castings or cast-welded structures. In order to improve the anti-cavitation and anti-sand wear performance, stainless steel can be deposited on cavitation-prone parts, or stainless steel blades, and sometimes the entire runner can be stainless steel. The use of a cast-welded structure can reduce costs, make the runner size more accurate, and the runner surface smoother, which is conducive to improving the efficiency of the turbine. It is also possible to use different materials to make the Guide Vane, upper crown and lower ring.
Francis turbines are mainly used in hydroelectric power generation. Hydropower is the use of rivers, lakes, and other high-potential water flows to the low, and the potential energy contained in them is converted into the kinetic energy of the turbine, which is to use the amount of water flow and the drop to rotate the water turbine. Then use the water turbine as the prime mover to drive the generator to generate electricity. Due to the low voltage of the power generated by the hydropower plant, if the voltage is to be transmitted to users at long distances, the voltage must be increased through a transformer, and then transmitted by the overhead transmission circuit to the substation in the user's concentration area, and once again reduced to suitable for home users the voltage of the electrical equipment in the factory, and the power is transmitted from the distribution line to the factories and household users.
The water turbine evolved from the ancient water wheel and waterwheel. The working process is that the water in the upstream reservoir passes through the dam diversion pipe and flows into the volute, water guiding mechanism and water turbine runner of the power plant under the dam, transforming the potential energy. The kinetic energy used to propel the runner blades to rotate. The runner is coupled with the generator rotor through the main shaft, which drives the rotor to rotate and cut the generator stator magnetic coil. The electromagnetic induction principle is used to generate high-voltage electricity in the generator coil, which is then boosted by the transformer and transmitted to the grid through the transmission line. The finished water in the turbine is discharged downstream through the dam tailpipe.