Optical arc flash protection: Real world experience

Bus differential systems have long been the main method of protection systems used on 5 kV and 15 kV electrical switchgear distribution applications. However these relays have some problem areas that must be addressed for each and every application. There are several types of bus protection relays such as the multi-restraint variable, high-impedance voltage-operated and LC linear coupler types. More recently, optical arc flash protection has been used for both bus differential as well as arc flash hazard reduction. While this system also uses current transformers, many of the problems that are inherent with the bus differential system are not issues with the optical arc flash protection. This paper will outline the recent installation that utilizes an optical Arc Flash protection system (AFD) at the Yale University Medical Campus for both Bus protection as well as arc flash hazard reduction. The design and application of the optical arc flash protection as well as the logic and hardware used in the design layout are discussed. An actual arc flash bus fault resulted in a real-life arc flash event which was successfully detected by the optical arc flash system. The fault was cleared before the bus differential protection could detect a fault. This paper details the events leading up to and culminating in the arc flash event as well as the responses of the various protective relays on the system.