Until now hydro-power machines (turbines and pumps) have had to be designed for a fixed rotational speed. These machines only fulfil their optimum efficiency at one specific operation point defined by head and flow rate. The variable speed controlled hydro- power machines designed, developed and applied in this project show technical and economic advantages over fixed rotational speed machines in pumped storage hydro-power unit applications. Conventional hydro-power technology has consisted of fixed rotation speed machines. This has meant that maximum efficiency is only obtained at one specific operation point. However, in practice hydro-power machines are usually operated in wide flow ranges which lead to several disadvantages. Firstly, significant efficiency losses in the operating range and narrow limits for the operating range. The aim of this project was to assess the possibilities and advantages of operating hydro-power machines at varying rotational speeds in three different areas: first, the control of small hydro-power plants by inverters; second small hydro-power plants with two fixed speeds; and finally, variospeed hydro-power machines in pumped storage hydro-power plants.