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