Publications

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Photovoltaic (PV) system certifications and codes have been modified to allow 1,500 V products onto the market which facilitate the plant engineering, procurement, and construction; however, the codes inadequately address the increased hazards to people and equipment in a high-voltage, photovoltaic plant that emanate from the rapid release of thermal energy, pressure waves, and electromagnetic interference of an arc-fault event. Existing calculations can contradict one another and are rooted in theory, not in physical testing. For this investigation, a localized arc-plasma model for a cylindrical geometry arc was developed from coupled electrodynamic, thermodynamic, and fluid mechanics equations, that were convolved together based on previous arc-discharge models [1]. The model was developed to assess incident energy, used for determining appropriate personal protective equipment (PPE), as a function of spark-gap current. To validate the model, preliminary experiments were performed at Sandia National Laboratories (SNL) with voltage levels as high as 1,500 V. Further utility-scale PV experiments were also conducted with current levels as high as 1,607 A to provide further data. Arc-stability, plasma column spectral features and radiative temperature rise were all evaluated during each respective test to provide radiated power values for validation. Overall preliminary results suggest a logarithmic increase in radiative power between 250 and 2800 W/cm for a current increase from 100 to 300 A.

Field tests of air-copper arcs were completed at a high-voltage, photovoltaic power plant using a simplified, 'arc-in-a-box' geometry to study dc arc-faults. Copper electrodes, 12.7 mm in diameter, were arranged in three configurations and an arc was initiated using < 700 VDCwith applied energy varying from 40-3900 kJ. Constitutive modeling of the arc-discharge predicts arc temperatures much greater than 1000 K. Two diagnostic techniques were fielded to characterize the spectral and thermal emission. Optical emission spectroscopy determined the time-resolved and mean arc temperatures were approximately T_{mean}= 7500 with standard deviations of ± 600 K, and infrared (IR) imaging mapped the mean temperature field, T_{mean}=1500\ \mathrm{K}, of the arc-heated environment.

Field tests of air-copper arcs were completed at a high-voltage, photovoltaic power plant using a simplified, 'arc-in-a-box' geometry to study dc arc-faults. Copper electrodes, 12.7 mm in diameter, were arranged in three configurations and an arc was initiated using < 700 VDCwith applied energy varying from 40-3900 kJ. Constitutive modeling of the arc-discharge predicts arc temperatures much greater than 1000 K. Two diagnostic techniques were fielded to characterize the spectral and thermal emission. Optical emission spectroscopy determined the time-resolved and mean arc temperatures were approximately T_{mean}= 7500 with standard deviations of ± 600 K, and infrared (IR) imaging mapped the mean temperature field, T_{mean}=1500\ \mathrm{K}, of the arc-heated environment.

Photovoltaic (PV) system certifications and codes have been modified to allow 1,500 V products onto the market which facilitate the plant engineering, procurement, and construction; however, the codes inadequately address the increased hazards to people and equipment in a high-voltage, photovoltaic plant that emanate from the rapid release of thermal energy, pressure waves, and electromagnetic interference of an arc-fault event. Existing calculations can contradict one another and are rooted in theory, not in physical testing. For this investigation, a localized arc-plasma model for a cylindrical geometry arc was developed from coupled electrodynamic, thermodynamic, and fluid mechanics equations, that were convolved together based on previous arc-discharge models [1]. The model was developed to assess incident energy, used for determining appropriate personal protective equipment (PPE), as a function of spark-gap current. To validate the model, preliminary experiments were performed at Sandia National Laboratories (SNL) with voltage levels as high as 1,500 V. Further utility-scale PV experiments were also conducted with current levels as high as 1,607 A to provide further data. Arc-stability, plasma column spectral features and radiative temperature rise were all evaluated during each respective test to provide radiated power values for validation. Overall preliminary results suggest a logarithmic increase in radiative power between 250 and 2800 W/cm for a current increase from 100 to 300 A.

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We present a detailed set of measurements from a piloted, sooting, turbulent C2H4-fueled jet flame. Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS) is used to monitor temperature and oxygen, while laser-induced incandescence (LII) is applied for imaging of the soot volume fraction in the challenging jet-flame environment at Reynolds number, Re = 20,000. A new dual-detection channel CARS instrument provides the enhanced dynamic range required in this highly intermittent and turbulent environment. LII measurements are made across a wide field of view requiring us to account for spatial variation in the soot-volume-fraction response of the instrument. Single-laser-shot results are used to illustrate the mean and rms statistics, as well as probability densities of all three measured quantities. LII data from the soot-growth region of the jet are used to benchmark the soot source term for one-dimensional turbulence (ODT) modeling of this turbulent flame. The ODT code is then used to predict temperature, oxygen and soot fluctuations within the soot oxidation region higher in the flame.

We present a detailed set of measurements from a piloted, sooting, turbulent C ₂ H ₄ - fueled diffusion flame. Hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS) is used to monitor temperature and oxygen, while laser-induced incandescence (LII) is applied for imaging of the soot volume fraction in the challenging jet-flame environment at Reynolds number, Re = 20,000. Single-laser shot results are used to map the mean and rms statistics, as well as probability densities. LII data from the soot-growth region of the flame are used to benchmark the soot source term for one-dimensional turbulence (ODT) modeling of this turbulent flame. The ODT code is then used to predict temperature and oxygen fluctuations higher in the soot oxidation region higher in the flame.

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