Adjustable speed operation of pumped hydroplants

With a frequency synchronous converter at the main terminals of a generator or at the collector rings of a three phase rotor it would be no longer necessary to tie the electrical machine synchronously to the grid, so the speed of the hydraulic turbine could be adjusted freely to satisfy the load demand at the maximum possible hydraulic efficiency. In this way the adjustable speed operation of a pumped hydro plant is an improvement in system performance and is a new flexibility in power plant site selection and sizing of hydro units. In the case of a HVDC link, where the high voltage AC-DC converter is already required, the possibility of variable speed operation is a further advantage to be added at savings in the transmission line costs. The author describes the improvements in system efficiency and the influence of this way of operation on the design of Panjiakou generators for China