Electrical safety, arc flash hazards, and "the standards" a comprehensive overview

Electrical safety and reduction of arc flash hazards are a priority in the petroleum and chemical industry. Due a growing need to address this critical concern, a wide variety of products, designs, and system modifications are available today from electrical equipment manufacturers. Various standards committees are addressing the issue by establishing new guidelines and standards such as IEEE P1584, aimed at limiting arc flash burns. The differences among the various standards have forced the power distribution engineer to consider and evaluate various standards to determine which is "best" for each particular application. Also, the guides and standards do not cover all possible conditions. The power distribution engineer must make choices related to basic system design alternatives when considering the many solutions available to reduce the hazards associated with arc flashes. The IEEE C37.20.7 Working Group has developed a technical paper (2001) to supplement their "Guide for Testing Medium-voltage Metal-Enclosed Switchgear for Internal Arcing Faults". Numerous papers have been written on the closely related subject of system grounding. Another challenge is achieving a higher level of personnel safety with existing power distribution equipment. In many cases, the existing equipment cannot be modified or retrofitted to meet the new standards and the power distribution engineer must find an alternative solution to enhance the equipment. This paper addresses internal arc testing as described by IEC, EEMAC, and the new IEEE Guide C37.20.7, and compares the critical requirements discussed in the various low-voltage and medium-voltage standards. It discusses several alternative solutions that can enhance the safety aspects or reduce incident energy levels in application of low-voltage and medium-voltage equipment, metal-clad and metal-enclosed. The authors also address the issue of incident energy levels in areas that exceed the level of personal protective equipment protection available. We provide examples from studies performed by a specific end user, comparing the existing incident energy values with those obtained after the introduction of a "safety-related" alternative. The authors also provide supplemental information regarding the advantages and disadvantages of some specific alternatives presently employed in the industry to enhance personal safety, including current limiting devices, ground fault protection, high speed ground switching, high resistance grounding, bus differential relay schemes, zone selective interlocking, on-line continuous partial discharge sensing and monitoring, and corona free insulation systems.