Renovating of existing pumped storage power plant from conventional system to adjustable speed system

The Grid frequency is mainly controlled by the thermal power units and the hydro power units. The thermal power units are operated even at night for frequency control, and it causes the increasing of the fossil fuel cost. Therefore, in order to save the fossil fuel costs, adjustable speed pumped storage unit has been required because it can change its generator-motor input at the pumping operation mode and control the grid frequency. This function contributes to the reduction of CO₂ emission as well. In this reason why we plan to improve the existing pumped storage power plant from the conventional type to the adjustable speed type. We can get the frequency control capacity of ±45MW/unit by renovating two fixed speed units. The construction work has been started last year. The first unit will start the commercial operation in 2013. This paper introduces the outline of our plan and its technical difficulties.