Arc Voltage Characteristics in Ultrahigh-Pressure Nitrogen Including Supercritical Region

IEEE Trans. Plasma Sci.

Støa-Aanensen

2019

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When the pressure and temperature of a fluid exceed a critical point, the fluid enters into the supercritical region. In this region, the physical properties are believed to be in favor of a good current interruption medium. This study focuses on the arc voltage characteristics of nitrogen arcs burning inside cylindrical tubes at different filling pressures: 1 bar, 20 bar, 40 bar, and 80 bar, thus covering the supercritical region. Two different tube materials have been used in the experiments; alumina and PTFE. Arc voltages are measured for arcs burning inside tubes of 2, 4, 8, and 15 mm inner diameters. In addition, free-burning arcs have been investigated at the same filling pressures. The arc current was 150 A at 350 Hz throughout the study. The arc voltage is found to increase with decreasing inner diameter of the tube at atmospheric pressure. At higher filling pressures (i.e., 20 bar, 40 bar, 80 bar), however, such a simple relationship is not observed. The arc temperature and radius have been calculated based on the 'simple theory of free-burning arcs' and the 'two-zone ablation arc model'. The calculated arc radius decreases with increasing gas pressure. Furthermore, due to increased absorption of radiation at high filling pressures, ablation is found less significant for ultrahigh-pressure nitrogen arcs compared to atmospheric pressure arcs. This is in line with the observations from optical micrographs of the inner surfaces of the tubes exposed to arcs at different filling pressures.

Section: A Arc Voltage Dependency On Inner Diameter Of the Tube At Dsupporting

confidence: 89%

Section: Resultsmentioning

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Section: Experimental Setup and Proceduresmentioning

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Section: A Free-burning Arcmentioning

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See 3 more Smart Citations

Ultrahigh-Pressure Nitrogen Arcs Burning Inside Cylindrical Tubes

IEEE Trans. Plasma Sci.

Støa-Aanensen

2019

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Thermal Interruption Performance of Ultrahigh-Pressure Free-Burning Nitrogen Arc

Lecture Notes in Electrical Engineering

Thimmappa

et al. 2019

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In this paper, an experimental investigation of the thermal interruption performance of free-burning nitrogen arcs at 1 bar, 20 bar, and 40 bar filling pressures is reported. This work contributes to the fundamental understanding of arc characteristics at very high gas filling pressures. A resonant circuit is used to generate an arc peak current of 130 A at a frequency of 190 Hz. An ignition copper wire initiates the arc between a 4 mm diameter pin electrode and a ring electrode. The arc burns freely at a fixed inter-electrode gap of 50 mm without any forced gas flow. A resistive-capacitive branch parallel to the arc controls the initial rate of rise of recovery voltage. By changing the parallel resistance, the rate of rise of recovery voltage is varied from 9.8 V/µs to 84.8 V/µs. Time to reignition and the corresponding re-ignition voltages are considered as the primary parameters to characterize the thermal interruption performance. It is observed that the re-ignition time rises with the decrease of rate of rise of recovery voltage at all pressure levels, which is expected. However, in the absence of a forced gas flow, high gas filling pressure results in a reduction of the time to re-ignition and the re-ignition voltage in contrast to atmospheric pressure nitrogen arc.

Arc Voltage Distribution Measurement in Tube Constricted Ultrahigh-Pressure Nitrogen Arc

Lecture Notes in Electrical Engineering

Støa-Aanensen

2019

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This work contributes to the fundamental understanding of axial voltage distribution of the arc burning inside polytetrafluoroethylene (PTFE) tube at very high filling pressures of nitrogen. The arc peak current of 85 A at a frequency of 190 Hz with a fixed initial rate of rise of recovery voltage (IRRRV) of approximately 50 V/µs is used throughout the study. Arc burning at three different filling pressures are studied: 1 bar, 20 bar, and 40 bar. To examine the axial voltage distribution in the arc, the arc voltage at three different axial position of the arc is independently measured. For some cases, a 3 cubic centimeter heating volume is attached to the ring electrode, which produces a back flow. For the cases with a heating volume, the pressure rise in the heating volume is also measured. It is observed that the pressure rise in the heating volume increases with the filling pressure. In the presence of the heating volume at a high filling pressure (i.e., 20 bar, 40 bar), the voltage drop increases significantly near the vent due to the relatively cold gas flow.