ABSTRACT
Protection relays have gone through major changes, from electromechanical to static and now to microprocessor-based multifunction programmable units. The development of multifunction programmable relays has changed the protection philosophy for many industrial power systems. This chapter outlines the limitations of equipment rating and provides guidelines to assist the designer in selecting adequate protection while ensuring a coordinated system. Surge protection is required for transformers at locations where they are subject to transient overvoltage produced by lightning and for switching surges from power factor capacitor-bank switching, and other system disturbances. Motor protection comprised a number of proven relays, each with individual features, in separate cases. Motor protection can be divided into four categories: protection against abnormal power supply conditions; protection against faults in the motor or motor feeder; protection against abnormal conditions caused by the driven load; and protection against abnormal conditions caused by environment.
