Field test results of DC arc fault detection on residential and utility scale PV arrays

It has been recognized that DC arcing faults pose a hazard in present photovoltaic (PV) systems. The 2011 National Electric Code [1] added a requirement for arc fault circuit protection and Underwrites Laboratories (UL) recently published an outline of investigation (UL1699B) to define the requirements for such a device. To satisfy the need for a PV arc fault detector (AFD) and test such a device in PV installations a method was developed for safely generating and recording DC series Arcing Faults within PV arrays. Field testing was performed on several residential and utility scale size PV systems. Results show that a DC Arc Fault Circuit Interrupter (AFCI) prototype was able to consistently detect and mitigate a series arcing fault under various operating conditions and without nuisance tripping. Analysis of electrical current waveforms confirmed that the spectral noise content is sufficient to detect arcing vs. non-arcing (baseline) conditions. This paper will include a general description of the arc generating apparatus used to safely insert a series arcing fault within a PV system, the test instrumentation used for measuring and recording arc voltage and current, and the results from testing a DC AFCI with various inverters, module technologies, PV array sizes and topologies, and under various illumination/operating conditions. The DC AFCI is able to detect and mitigate series arcing faults significantly faster than the ignition/burn through times established for PV insulation materials and within the trip times established by UL1699B [2]. Test results show that series arcing faults can be detected by a DC AFCI on a single string of either silicon or thin film type PV modules, and without a DC AFCI nuisance tripping when located on a non-faulted parallel string.