Horizontal Francis Hydro Turbine / Francis Water Turbine with Water Head From 20m to 300mFrancis turbines are most widely used among water head from 20m to 700mm. A Francis turbine has a runner with fixed blade, usually nine or more. Water is introduced just above the runner and all around it and then falls through, causing it to spin. Besides the runner, the other major components are the spiral case, wicket gates, and draft tube. Most small Francis turbine are horizontal shaft and metallic spiral case, it has two bearing assembled on the generator seat.
Water flows through penstock of the power station, Butterfly valve, expansion pipe, inlet tube, spiral case and wicket gates into the runner, and then it drives the runner to revolve and convert hydraulic energy into mechanical energy and drives the rotor of generator revolution by the force of the main shaft of turbine, thus converting the mechanical energy into electric energy.
Franics Turbine runner compose of the blade, upper crown, bend and cone.
The whole rotating part is mainly composed of the runner, main shaft, flywheel and main sealing assembly etc. The main shaft is laid in horizontal or vertical position. The runner cone is keyed on the end of the main shaft, and locked with bolt, The other end of the main shaft is connected to the flywheel. The runner is the principal component of the turbine convert hydraulic energy into mechanical energy. The main sealing assembly adopts polyethylene packing structure to prevent water leaking out, and should be connected the clean and pressure water which pressure is 0.15~0.25MPa.
The spiral casing is the largest part of the hydraulic turbine and erecting bench- mark. It is made of steel-welding structure. Together with spiral casing and stay ring. Some stay vanes are equipped on the inner of stay ring. A pressure gauge is equipped to measure the pressure of the inlet water there. On the top of the spiral casing, it presents an air-discharge valve, which is used to expel out the residual air in the shell, when the shell is filled with water before starting up the turbine.
The distributor consists of wicket gates, guide vane arms, shear pins, regulating ring, head cover, bottom ring etc.
The wicket gates function is to regulate the discharge of water flow. so as to suit the regulation on various loads.
The opening of wicket gates can be regulated by the governor servomotor, to guarantee the revolving speed constant when the load changes. When the turbine is shut down all openings between the wicket from flowing into the runner. Each wicket gate swivels in bushing along, the axial line of its stem. The lower bushing seats in the head cover, the middle and upper bushing seat in the bottom ring. The connecting rod mechanism is equipped between the wicket gates and regulating ring in order to transfers their move and force.
Also the shear pins are equipped on the distributor. When the turbine is shut down if the closing of the wicket gates exists obstacles, the shear pin related to the opening will be shorn so that the other pats of distributor many not be damaged. The regulating ring is connected with the servomotor by way of the connecting rod.
The draft tube consists of draft tube, draft tube cone and draft tube bend etc. It’s function is to guide water current and receive some hydraulic energy.