Brief Descriptions of Francis turbine

Francis turbines can be designed for a wide range of heads and flows and are the most common water turbine in use today. The Francis turbine has the characteristics of simple structure, small size, low cost, high efficiency at full capacity (typically over 90%), stable in running, applicable to a wide range of water heads.

The Francis turbine is a type of reaction turbine, a category of turbine in which the working fluid comes to the turbine under immense pressure and the energy is extracted by the turbine blades from the working fluid. A Francis turbine consists of the following main parts: Spiral Casing, Guide or Stay Vanes, Runner Blades, Draft tube, etc.. 

Francis turbines are almost always mounted with the shaft vertical to keep water away from the attached generator and to facilitate installation and maintenance access to it and the turbine.

Application scope
Application scope of heads: 10m ~ 650m 
Runner diameters: 1.0 m ~ 10.0m 
Installable capacity: 200KW ~ 200000KW 
Specific ratio speed: 50 ~ 300

Wicket gates around the outside of the turbine's rotating runner adjust the water flow rate through the turbine for different water flow rates and power production rates.

In addition to electrical production, Francis turbines may also be used for pumped storage, where a reservoir is filled by the turbine (acting as a pump) driven by the generator acting as a large electrical motor during periods of low power demand, and then reversed and used to generate power during peak demand. These pump storage reservoirs, etc. act as large energy storage sources to store "excess" electrical energy in the form of water in elevated reservoirs. This is one of only a few ways that temporary excess electrical capacity can be stored for later utilization.

Composition of Francis turbine

Embedded parts, water distributor, rotation parts, auxiliary parts and arrangement parts.

Main parts of Francis turbine

Spiral casing: It makes the water flow to produce circular motion, and guides the water flow evenly and axisymmetrically into the turbine. 

Seat ring: It is located in the periphery of the water blades, consists of the upper and lower ring and the upright column.
It is the skeleton of turbine, bearing the loads of turbine pier and external parts, transmitting them to the lower foundation and supporting the movable guide vane. 
Section design: Streamline shape to guarantee strength and stiffness. Its numbers are half of the movable guide vane. 

Water distributor: It adjusts the discharge of turbine and changes the output according to the load change of the Unit.; It also guides the water flow into the runner as tangent direction to form speed-torque. 
Composition: Water blades with its bearings, governor, servomotor (tumbler, connecting rod, control ring). 

Runner: The main part for converting water energy to mechanical energy
Composition: Bearing, runner crown, blade, band, wearing ring, runner cone.

Draft tube: The function of draft tube is to guide water flow into downstream channel and recycle part of kinetic energy and potential energy.