Protective device coordination-ideal and practical

A relay coordination study should ensure maximum protection of the system components with minimum load removed from the service. It is noted that compromises will be necessary in this objective and that each compromise should receive critical considerations in terms of specific requirements of the plant operations, availability of equipment for restart, and possible damage. It is demonstrated that protective device coordination is not only a fag-end activity, but also a front-end activity that impacts system design and performance. A step-by-step analysis is performed of the coordination of protective devices in an arbitrary multivoltage level distribution system with in-plant generation and a utility tie. Coordination at 480 V, 2400 V, and 13.8 kV distribution is examined under full plant operations and when the short-circuit levels on the system are considerably reduced with only an in-plant generator in operation. The compromises necessary in each situation and the possible improvements are discussed.<>