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.