Abstract
Wall-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.
Highlights
For modern power transmission and distribution grids, high voltage circuit breakers are among the essential elements to ensure safe power flow [1,2]
The general structure of the tubular and separated nozzles were similar. They were made of PTFE doped with
In this article the main focus is set on the time around current zero (CZ) while the starting phase is of minor interest
Summary
For modern power transmission and distribution grids, high voltage circuit breakers are among the essential elements to ensure safe power flow [1,2]. Basic technology applied are self-blast circuit breakers in which a pressure build-up in a heating volume, necessary for arc quenching around current zero (CZ), is produced by the ablation of material from the nozzle wall due to intense arc radiation. Gas sulfur hexafluoride (SF6 ) is applied as quenching and insulating gas due to its unique properties as being chemically inert, non-flammable, non-explosive, non-toxic, thermally stable, and an excellent electrical insulator and arc interrupter due to its high electronegativity (electron attachment) and density [3]. Metal-doped polytetrafluoroethylene (PTFE) is used as the nozzle material due to well-adjustable ablation, pressure built-up, and dielectric properties. A variety of alternative gases has been discussed and tested in the last decades, e.g., CO2 , CF3 I, C2 F4 , c-C4 F8 , C4 F7 N, and C5 F10 as pure gases or in mixtures of Energies 2020, 13, 4714; doi:10.3390/en13184714 www.mdpi.com/journal/energies
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