Enhancing Electrical Braking in Synchronous Machines to Improve Reversible Operation of Pumped Hydro Storage Plants

Pumped hydro storage plants (PHSP) are the leading solution to enable massive renewable energy penetration in power systems. In binary PHSP, which are the most commonly used, the change of working mode of the synchronous machine (SM) from turbine mode to pump mode, or vice versa, requires disconnecting the machine from the grid, closing the distributor, braking the machine through mechanical and/or electrical methods and starting it up in the opposite rotation direction. To improve the electrical braking of SM in PHSP, this paper proposes to shortcircuit the high-voltage side of the main power transformer instead of the SM terminals, as it is normally done. Consequently, faster braking and operation mode changing are achieved, increasing the response capacity of these power plants. Numerous laboratory experimental tests have been carried out to test the proposed method and to compare it with the conventional electrical braking method. Additional methodology validations have been carried out through calibrated simulations for large PHSPs using real 106-MVA pumping group parameters. Both experiments and simulations reached satisfying results obtaining reductions of around 20% in the braking times.