All your eggs in one basket [back-up protection using multifunction relays]

Multifunction microprocessor-based relays are commonly used in modern installations due to the many advantages they offer, such as communications, measurements, simplified wiring, self monitoring, and reduced space requirements. A reliable protection scheme is very important in order to protect capital equipment and operating personnel and reduce down time by selectively clearing faults. Back-up protection is also normally provided to ensure the elimination of faults should the primary protection circuit fail. In this article, the authors show how the features of modern multifunction relays can be used to enhance back-up protection. To better understand why multifunction relays can improve back-up protection, it is necessary to first review what back-up protection is and how it has been implemented in the past. This review is based on the electrical distribution system typically found in large petrochemical installations.