David Franklin, P.E. ESSB Winter 2017 DC Arc Flash David Franklin, P.E. ESSB Winter 2017
How did we get here? Increased use of DC (PV, Wind Turbines and other Stored Energy means) IEEE 1584 only focuses on AC NFPA 70E-2015 only standard that discusses DC Existing calculation methods too conservative Requires excessive PPE Increased approach boundaries
What’s wrong with being conservative? Difficult to perform online maintenance Cost impacts Space limitations
NFPA 70E-2015 Basis Reference NFPA 70E-2015 Annex D.5. Perform DC Arc Flash Risk and Hazard Assessment Arc Flash Incident Energy based on Maximum Power Method Maximum power delivered at when Varc = 0.5 x Vsource Arcing Current - Iarc = ½ Ibf, DC Incident Energy - IEin = 0.01 x Vsource x Iarc x Tarc / D2 Tables provided in 70E commensurate with arc flash energies.
Other Calculation Methods Linear Solution, Ohm’s Law – Iarc = Vsource / (Rarc + Rbatt + Rcable) Have to determine Rarc though ETAP DC AF Module Circuit iteration through assuming Iarc (typically start at ½ If) Stokes and Oppenlander – Rarc = (20 x 0.534 x zg) / Iarc0.88