scope:

This application guide presents generally accepted methods of protection for ac motors. It identifies and summarizes the functions necessary for adequate protection of motors based on type, size, and application. The recommendations in this guide are based on typical installations. Information relating to protection requirements, including microprocessor based protection systems, applications, and setting philosophy is provided to enable the reader to determine required protective functions for motor installations. Relay protection of squirrel-cage, wound-rotor induction motors, and synchronous motors is presented herein. This guide also summarizes the uses of relays and devices, individually and in combination, so the user may select the necessary equipment, to obtain adequate motor protection. This guide is concerned primarily with the protection of three-phase, integral horsepower motors and adjustable-speed drives where specifically indicated. This guide does not purport to detail the protective requirements of all motors in every situation. What it does provide is enough information and guidance to implement adequate protection for most applications.