Upgrading a conventional pump turbine to a variable speed machine

With the increase in renewable energy being added to power grids, more storage for electricity is also needed as well as faster plant regulation, and an increased capacity for regulation. Currently, pumped-storage plants provide the most cost-effective means of storing large amounts of energy, while at the same time compensating for large wind power fluctuations into the grid. Variable speed technology can offer additional network flexibility to conventional pumped storage, by allowing power regulation in the pumping mode. The paper will discuss the benefits of variable speed units in a pumped-storage scheme from an electricity grid perspective, as well as examining the challenges faced when replacing a 1975 vintage synchronous generator motor with a modern double-fed induction machine.