Adjustable speed asynchronous machine in hydro power plants and its advantages for the electric grid stability.

Abstract

Since a long time, it is known that hydraulic machines can work with an increased efficiency at partial load when the speed can be adapted to this partial load. In a standard configuration when the hydraulic machine is coupled to a synchronous machine which is directly connected to the electric grid this speed variation is not possible at all. The use of a static frequency converter which is inserted between the grid and the stator is a well known solution to achieve an adjustable speed machine. Adjustable speed drive systems have already been applied in the past to hydro power plants. Up to now they have mainly been used for start-up purposes of pumps or pump-turbines. The used converters were therefore rather small in respect of converter power output (< 30 MVA).