Arc-flash incident energy reduction using zone selective interlocking

As a result of new requirements in NFPA 70E, many facilities are performing arc-flash hazard analyses to better understand how to protect personnel from the possibility of being injured in an arc-flash incident. In many cases in the petrochemical industry, it is unsafe or not practical to shut down electrical equipment to do work. This paper explores practicable options that a facility has to reduce incident energy levels in existing low-voltage systems where the arc-flash hazard analysis results in unacceptably high levels. It will also explore a case study, in the Gulf of Mexico, where an offshore oil production platform was able to cost effectively reduce incident energy levels from approximately 170 calories/cm2 to under 15 calories/cm2 by implementing a zone selective interlocking system into their low-voltage switchgear. The selection process logic involving equipment, personnel considerations and commissioning will all be addressed.