Device miscoordination affects plant reliability

In most industrial situations, the power system is constantly changing. New loads are being added as the plant grows or processes are being modernized. These additions may inadvertently result in overall protection scheme characteristics that may not be desirable. This situation may only become apparent after a fault event results in unexpected breaker operations. A coordination study of an entire plant power system may be necessary to uncover these unintended coordination issues, as well as determine solutions to the problems. Examples resulting from the examination of a chemical facility distribution system where the 4160 volt system is resistance grounded, limiting the ground fault current to 2000 amperes are discussed. In most cases, the 480 volt system is high resistance grounded. Solidly grounding the 480 volt system is also briefly discussed. Several examples are discussed to show the plant layout, the existing protective devices, a description of the coordination problem and the solution proposed