scope:

This application guide describes the generally accepted forms of protection for the synchronous generators and their excitation systems. It summarizes the use and selection of relays and other protective devices that provide generator protection. The guide is primarily concerned with protection against faults and abnormal operating conditions for large hydraulic, steam, and combustion turbine generators.

The guidance pertains to typical synchronous generator installations. However, sufficient background information relating to protection requirements, applications, and setting philosophy is given to enable the reader to evaluate the need to select and to apply suitable protection for most situations. The protective functions discussed in this guide may be implemented with a multifunction microprocessor based protection system (digital system). The protection philosophy, practices, and limits are usually similar to those of the implementation using discrete component relays. The algorithms used to perform some of the protection may be different, but typically provide equivalent or better protection. The protection performance and capability may be superior using the digital systems such as improved frequency response (bandwidth) and thresholds (pickup settings). Other additional features may be available from these digital systems that enhance the functionality such as monitoring and reporting.

This guide does not purport to detail the protective requirements of all generators in every situation. For example, standby and emergency-use generators are specifically excluded.

Purpose

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