The Kaplan turbine is a hydraulic jet turbine that uses small gradients, up to a few tens of meters, but with large flows, from 200/300 m³ / s. It is therefore a type of turbine used in hydropower, a type of renewable energy.
The Kaplan turbine was invented in 1913 by the Austrian professor Viktor Kaplan.
Constructively, this type of hydraulic turbine is a propeller, where the blades can be oriented, since the water flow varies, which allows the performance to remain high up to flows of 20-30% of the nominal flow. In general, the turbine is equipped with fixed stator deflectors that orient the flow. The efficiency of the turbine can be optimized for a wider range than the ideal flow through a system of orientation of the stator deflectors when the flow varies.
The liquid reaches the Kaplan turbine thanks to a spiral duct that feeds the entire circumference, then passes through a distributor that gives the fluid a rotating rotation, essential to impart the movement to the impeller, where the diverted flow of 90 ° reverses it axially.
In the exhaust, as for the Francis turbine, it is possible to recover energy thanks to the diffuser.
Characteristics of the Kaplan turbine
With a propeller turbine, the regulation is practically nil, so it can only work for a certain range, so the distributor is not even adjustable.
With the Kaplan turbine thanks to the orientation of the impeller blades, it is possible to adapt to the current flow. This is because each adjustment of the distributor corresponds to an orientation of the blades and this allows you to work with very high yields (up to 90%) in a wide range of flow rates.
The field of use of the Kaplan slow turbines reaches maximum drops of around 80 m and flows up to 50 m³ / s, partially overlapping the field of use of the Francis rapid turbines, which reach falls of less than 10 m and can exceed 300 m³. / s
It is common to use both propeller turbines and Kaplan turbines: the propeller turbines will operate at full capacity and any excess fluid will be allocated to the Kaplan turbines, whatever their size. This limits installation costs because a Kaplan turbine is more expensive than a propeller turbine, so the installation of Kaplan turbines in a hydropower plant would be much more expensive.