Protective relaying an medium- and high-voltage system

For this article we reviewed unusual outages, such as nonselective device operations during a fault, at different petroleum industry facilities. We found that changing some types of protective devices and modifying device settings improved both reliability and on-line performance. The following categories of protection problems were reviewed: ground faults on 12 kV feeders; ground faults on 4 kV motor feeders; faults on 115 kV transmission lines; and overexcitation of equipment. Each case is presented with: a brief synopsis of the problem encountered; our evaluation of the problem, including suggested solutions; and the “lessons to be learned” and trouble spots to avoid