Joseph Charles Zuercher

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.

Electrical Arcing and Material Ignition Levels

Experimental data and analysis show the relationship between arcing watts, the time of the arc exposure and the degree to which common polymers experience damage. Arcing test apparatus for 125V DC and 48 volt DC are shown. Arc gap control allows 125-volts to mimic arcs in lower voltage systems. Arcing current waveforms depict the chaotic behavior of arcs and differences due to anode / cathode materials. Levels of degradation are defined and used for “Constant Damage Contours” for Vinyl, Carpeting and Sound insulation. The polymers were exposed to conditions of constant arcing watts for increasing times. Connecting the points of “first flame” establishes a “contour of constant damage”. The data indicates that a “3 second flame free” limit is between 50 and 100 watts. 4000 watts of arcing takes 1/4 to ½ second to cause burning. The influence of circuit resistance on the maximum arc power transfer is presented.

Practical considerations in pulse-echo radar for short range sensing

In this paper, we present the principle of operation, design, and testing of a pulse echo radar unit that utilizes the properties of short helical antennas. Data was captured for targets approaching the radar at three different controlled velocities, three different target sizes, and three radar range gate settings. These data reveal the expected Doppler frequency as well as a second anomalous frequency. The effects of multipath signals, separated transmit and receive antennas, and direct antenna coupling are used to explain this anomalous frequency. These effects are mathematically simulated, and the results compare favorably with the test data.