Kaplan turbines
The solution for low head applications within a head range of up to 80 m
Invented by the Austrian Professor Viktor Kaplan in 1913, the Kaplan turbine formed the basis of a new turbine technology. Today it is considered a classic. The concept is feasible within a head range of up to 80 m. Runners with 4 to 7 blades cover the whole range.
ANDRITZ HYDRO has experience in runner diameters up to 10,000 mm and outputs up to 200 MW. Semi-spiral concrete for lower heads and full steel plate spiral casing concepts can be utilized. The total installed capacity is approximately 50,000 MW, and ANDRITZ has installed around 3,200 large units worldwide.
After the spiral case, the water passes the fixed stay vanes and then the moveable wicket gates which, in addition to the runner, is a device for adjusting the water discharge, and as a result also the turbine output. The wicket gates are connected via levers and links to the regulating ring, which is moved by two double-acting servomotors.
The runner consists of the stainless steel runner blades mounted on the runner hub and the runner cap at the lower side of the hub, enhancing the optimized hydraulic shape. The runner blades are moveable and are the second device to adjust the water discharge and turbine output. The blade movement is operated by a servomotor integrated into the runner hub. Due to these moveable blades, the Kaplan turbines show a high efficiency level (flat Kaplan curve) over the entire operating range. In some applications, where a more or less constant water flow can be guaranteed, the Kaplan turbine can be designed with fixed runner blades where the efficiency drop at full and part load is higher (comparable to the Francis turbines). In order to avoid cavitation at the periphery of the runner, “anti-cavitation lips” are provided on the suction side of the runner blades for heads above 20 m.
This type of Kaplan turbine is often used for run-of-river projects, thus recent design development has been geared towards environmental topics. The oil-free hub is one result of this, where the runner hub oil is replaced by water.
