Case studies in arc flash reduction to improve safety and productivity

With the advent of new power system analysis software, a more detailed arc flash analysis can be performed under various load conditions. These new ldquotoolsrdquo can also evaluate equipment damage, design systems with lower arc flash, and predict electrical fire locations based on high arc flash levels. This paper demonstrates how arc flash levels change with available utility MVA (mega volt amperes), additions in connected load, and selection of system components. This paper summarizes a detailed analysis of several power systems to illustrate possible misuses of 2004 NFPA 70E Risk Category Classification Tables while pointing toward future improvements of the Standards. In particular, findings indicate upstream protection may not open quick enough for fault on the secondary of a transformer or at the far end of a long cable due to the increase in system impedance. Several examples of how these problem areas can be dealt with are described in detail.