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- ItemAblation-dominated arcs in CO2 atmosphere—Part I: Temperature determination near current zero(Basel : MDPI, 2020) Methling, Ralf; Khakpour, Alireza; Götte, Nicolas; Uhrlandt, DirkWall-stabilized arcs dominated by nozzle–ablation are key elements of self-blast circuit breakers. In the present study, high-current arcs were investigated using a model circuit breaker (MCB) in CO2 as a gas alternative to SF6 (gas sulfur hexafluoride) and in addition a long polytetrafluoroethylene nozzle under ambient conditions for stronger ablation. The assets of different methods for optical investigation were demonstrated, e.g., high-speed imaging with channel filters and optical emission spectroscopy. Particularly the phase near current zero (CZ) crossing was studied in two steps. In the first step using high-speed cameras, radial temperature profiles have been determined until 0.4 ms before CZ in the nozzle. Broad temperature profiles with a maximum of 9400 K have been obtained from analysis of fluorine lines. In the second step, the spectroscopic sensitivity was increased using an intensified CCD camera, allowing single-shot measurements until few microseconds before CZ in the MCB. Ionic carbon and atomic oxygen emission were analyzed using absolute intensities and normal maximum. The arc was constricted and the maximum temperature decreased from > 18,000 K at 0.3 ms to about 11,000 K at 0.010 ms before CZ. The arc plasma needs about 0.5–1.0 ms after both the ignition phase and the current zero crossing to be completely dominated by the ablated wall material. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemAblation-dominated arcs in CO2 atmosphere—Part II: Molecule emission and absorption(Basel : MDPI, 2020) Methling, Ralf; Götte, Nicolas; Uhrlandt, DirkMolecule radiation can be used as a tool to study colder regions in switching arc plasmas like arc fringes in contact to walls and ranges around current zero (CZ). This is demonstrated in the present study for the first time for the case of ablation-dominated high-current arcs as key elements of self-blast circuit breakers. The arc in a model circuit breaker (MCB) in CO2 with and an arc in a long nozzle under ambient conditions with peak currents between 5 and 10 kA were studied by emission and absorption spectroscopy in the visible spectral range. The nozzle material was polytetrafluoroethylene (PTFE) in both cases. Imaging spectroscopy was carried out either with high-speed cameras or with intensified CCD cameras. A pulsed high-intensity Xe lamp was applied as a background radiator for the broad-band absorption spectroscopy. Emission of Swan bands from carbon dimers was observed at the edge of nozzles only or across the whole nozzle radius with highest intensity in the arc center, depending on current and nozzle geometry. Furthermore, absorption of C2 Swan bands and CuF bands were found with the arc plasma serving as background radiator. After CZ, only CuF was detected in absorption experiments. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemElectrical Modelling of Switching Arcs in a Low Voltage Relay at Low Currents(Basel : MDPI, 2020) Najam, Ammar; Pieterse, Petrus; Uhrlandt, DirkThe arc behaviour of short, low current switching arcs is not well understood and lacks a reliable model. In this work, the behaviour of an arc in the air is studied during contact separation at low DC currents (0.5 A to 20 A) and for small gap lengths (0 mm to 6 mm). The experiments are performed on a low voltage relay with two different electrode configurations. The arc voltage is measured during the opening of the contacts at constant current. The arc length is determined optically by tracing the mean path of the arc over time from a series of high-speed images. From the synchronised data of voltage vs. distance, first a sudden jump of the voltage at the start of contact opening is observed. Secondly, a sudden change in the voltage gradient occurs as the arc is elongated. Short arcs with a length up to approximately 1.25 mm show an intense radiation in the overall gap region and high voltage gradients. An unexpected behaviour never reported before was observed for longer arcs at low current: Two characteristic regions occur, a region in front of the cathode, with a length of approximately 1.25 mm, having an intense radiation and a high voltage gradient as well as a region of much lower radiation intensity and a comparatively lower voltage gradient in the remaining gap area despite a small anode spot region. The characteristic border of approximately 1.25 mm is almost independent of the current. A generalised arc voltage model is proposed based on the assumption that a constant sheath voltage and two discrete field regions exist, which are modelled as two independent linear functions of voltage vs. length. The data for various currents is combined to yield a general non-linear function for predicting the arc voltage vs. arc length and current.
- ItemProperties of vacuum arcs generated by switching RMF contacts at different ignition positions(Basel : MDPI, 2020) Gortschakow, Sergey; Franke, Steffen; Methling, Ralf; Gonzalez, Diego; Lawall, Andreas; Taylor, Erik D.; Graskowski, FrankThe influence of initiation behavior of the drawn arc on the arc motion, on arc characteristics during the active phase, as well as on the post-arc parameters, was studied. The study was focused on arc dynamics, determination of the anode surface temperature after current interruption, and diagnostics of metal vapor density after current zero crossing. Different optical diagnostics, namely high-speed camera video enhanced by narrow-band optical filters, near infrared spectroscopy, and optical absorption spectroscopy was applied. The initiation behavior of the drawn arc had a clear influence on arc parameters. Higher local electrode temperature occurs in case of the electrodes with ignition point near the outer electrode boundary. This further causes an enhanced density of chromium vapor, even in cases with lower arc duration. The results of this study are important for design development of switching RMF contacts for future green energy applications. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemRES-Q-Trace: A Mobile CEAS-Based Demonstrator for Multi-Component Trace Gas Detection in the MIR(Basel : MDPI, 2018-6-27) Lang, Norbert; Macherius, Uwe; Zimmermann, Henrik; Glitsch, Sven; Wiese, Mathias; Röpcke, Jürgen; van Helden, Jean-Pierre H.Sensitive trace gas detection plays an important role in current challenges occurring in areas such as industrial process control and environmental monitoring. In particular, for medical breath analysis and for the detection of illegal substances, e.g., drugs and explosives, a selective and sensitive detection of trace gases in real-time is required. We report on a compact and transportable multi-component system (RES-Q-Trace) for molecular trace gas detection based on cavity-enhanced techniques in the mid-infrared (MIR). The RES-Q-Trace system can operate four independent continuous wave quantum or interband cascade lasers each combined with an optical cavity. Twice the method of off-axis cavity-enhanced absorption spectroscopy (OA-CEAS) was used, twice the method of optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS), respectively. Multi-functional software has been implemented (i) for the general system control; (ii) to drive the four different laser sources and (iii) to analyze the detector signals for concentration determination of several molecular species. For the validation of the versatility and the performance of the RES-Q-Trace instrument the species NO, N2O, CH4, C2H4 and C3H6O, with relevance in the fields of breath gas analysis and the detection of explosives have been monitored in the MIR with detection limits at atmospheric pressure in the ppb and ppt range.