Study On Detection Characteristics And Prevention Strategies Of DC Fault Arcs In PV Systems

In recent years, the total installation and generation capacity of solar photovoltaic improved dramatically due to important technology progress, significant cost reductions, and forceful political support. According to the IEA (International Energy Agency) report "World Energy Outlook 2013," the worldwide power generation from solar PV installations increased by 50% per year over the last decade. The rapid expansion of PV installations leads to not only clean energy supply, but also potential hazards. Especially since 2006, reports have claimed that fire accidents in residential, commercial, and utility PV installations happened more frequently than before. Subsequent investigation proved that most of the electrical fire arose from DC arcs. The fault DC arcs in PV systems are dangerous with high voltage and temperature, which can also ignite the flammable substance around and start a fire. The fire in PV systems is hard to put out by conventional means because the power source cannot be de-energized as long as the panels are exposed in daylight. In this case, National Electrical Code(?) (NEC) 2011 added the requirements of DC arc-fault circuit protection in the section of 690.11 that PV system with maximum system voltage of 80 volts or above shall be protected by a DC arc-fault circuit interrupter (AFCI). Therefore, it is urgent to study the characteristics and prevention strategies of DC fault arcs in PV systems.This paper summaries the current studies about photovoltaic DC arc-fault protection methods and products, and introduces the model of PV systems and arcs, arc types and the principle of detection algorithms. According to current conditions, field experiments were conducted to generate DC arcs in a small PV power station based on an arc generator controlled by a step motor. Experiment data were collected and saved through high-precision sensors and an oscilloscope. Six arc characteristics and responding thresholds were concluded and calculated by analyzing the off-line data.In this paper, the arc detection algorithm based on multiple criteria was proposed for the protection of series DC arcs. Meanwhile, various prevention strategies against different types of parallel arcs were also present according to arc locations and circuit topologies.The research on DC arc faults in PV systems in this paper is deemed as a relatively new field in China. This study contributes to the improvement of electrical safety and the formulation of relevant standards, providing AFCI manufacturers with guidance and reference.