This guide has been prepared to assist the protection engineer in applying relays for the protection of generating plant equipment from damage caused by operation at abnormal frequencies including overexcitation.

This application guide assists the protection engineer in applying relays for the protection of synchronous generating plant6 equipment from damage caused by operation at abnormal frequencies including overexcitation. Consideration is given to the effect of abnormal frequency operation on those associated station auxiliaries whose response can affect plant output. The guide also presents background information regarding the hazards caused by operating generation equipment at abnormal frequencies. It documents typical equipment capabilities and describes acceptable protective schemes. Underfrequency protection can be provided by load shedding and/or a discrete underfrequency protection scheme. Guidance is provided to help meet requirements from regulatory bodies. The protective functions discussed in this guide may be implemented with a multifunction microprocessor-based protection system.

This guide summarizes the use of relays and devices such that the reader may select the necessary equipment to provide adequate protection for ac generators from abnormal frequency conditions.