Abstract
Molecule 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.
Highlights
Self-blast circuit breakers represent one of the main technologies for high-current interruption at high voltage
The molecule CuF is expected when copper vapor from the electrode erosion is mixed with the dissociated PTFE vapor from the nozzle ablation [10]
Ablation-dominated switching arcs have been investigated in a model circuit breaker with CO2 atmosphere as well as in a long PTFE nozzle under ambient conditions
Summary
Self-blast circuit breakers represent one of the main technologies for high-current interruption at high voltage. Intense radiation emitted from the high-current arc leads to a considerable photo-ablation of the surrounding nozzle which causes a pressure buildup and a strong gas flow necessary for arc quenching around current zero (CZ) [1,2]. The substitution of the greenhouse gas SF6 by more environmentally-friendly gases like CO2 is an actual trend. The pressure buildup due to strong arc radiation and nozzle ablation, as well as the arc quenching processes, are key issues of the successful current breaking and have been subject to a large number of scientific studies. The main questions concern the properties of the arc and the hot gas regions like temperatures and species densities which are required for a sufficient understanding of the processes
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