Quantifying Photovoltaic Fire Danger Reduction with Arc-fault Circuit Interrupters

Unmitigated arc-faults present fire dangers, shock hazards, and cause system downtime in photovoltaic (PV) systems. The 2011 National Electrical Code® added section 690.11 to require a listed arc-fault protection device on new PV systems. Underwriters Laboratories created the outline of investigation for PV DC arc-fault circuit protection, UL 1699B, for certifying arc-fault circuit interrupters (AFCIs) for arc suppression. Unfortunately, little is known about appropriate trip times for arc-faults generated at different locations in the PV system, with different electrode and polymer encapsulant geometries and materials. In this investigation, a plasma model was developed which determines fire danger with UL 1699B-listed AFCIs and consequences of arc-fault discharges sustained beyond UL 1699B trip time requirements. This model predicts temperatures for varying system configurations and was validated by 100 and 300 W arc-faults experiments where combustion times and temperatures were measured. This investigation then extrapolated burn characteristics using this model to predict polymer ignition times for exposure to arc power levels between 100-1200 W. The numerical results indicate AFCI maximum trip times required by UL 1699B are sufficient to suppress 100-1200 W arc-faults prior to fire initiation. Optical emission spectroscopy and thermochemical decomposition analysis were also conducted to assess spectral and chemical degradation of the polymer sheath.