Arc Flash Hazards of 125 Vdc Station Battery Systems

Arc flash incident energy studies are critical in determining appropriate personal protective equipment for electrical workers. While ac incident energy calculation methods have been refined based on extensive testing, available methodologies for calculating dc incident energy rely on conservative assumptions due to lack of experimental results. Consequently, workers may be unnecessarily encumbered with excessive PPE. To better quantify the dc arc flash hazard that Bonneville Power Administration employees are exposed to, laboratory testing was performed to replicate the most severe conditions electrical workers were likely to encounter. Using a flooded lead-acid station battery, faults were initiated, such that fault current and incident energy could be measured. Results showed that industry-standard arc models overestimate the incident energy by more than a factor of ten. It was concluded that BPA electrical workers were not reasonably exposed to more than 4 Cal/cm
²
, and required PPE was reduced to Level 1 for all 125 VDC station battery circuits.