Upgrading of hydrogenerator excitation systems

Whereas hydroelectric stations are continuing to deliver low-cost energy, in some cases after 75 years´ service, certain peripherals of the generation units become obsolete after thirty years. Excitation systems in particular have required partial or total replacement, to provide: more stringent voltage regulation, enhanced stability of the sytems, less costly maintenance, and suitability for automation and control from a remote location. This paper compares typical retrofitting options ranging from replacement of pilot exciters and rheostatic voltage regulators to complete replacement of the excitation systems by thyristor-based equipment. The upgrading of excitation systems to enhance power system stability has been the first and most significant application of power electronics to the reliability of electrical supply networks