Dielectric Recovery of a.c. Arcs in Turbulent Gases

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Abstract
It is pointed out that arc extinction in modern high voltage alternating‐current circuit interrupters is actually achieved by subjecting the confined arc to a turbulence‐producing gas blast, thus accelerating the arc's dielectric recovery near current zero. Experiments to investigate the effects of gas velocity, gas composition, arc current magnitude, and constriction of the arc space upon the rate of recovery of dielectric strength by the arc near current zero are described. Results of these experiments show that most of the dielectric recovery occurring in a turbulent arc space within a hundred or so micro‐seconds of current zero takes place before the actual moment of zero current. With a 600‐ampere confined arc in carbon dioxide, it was found that the dielectric strength at current zero could be increased from 100 to 215 volts per centimeter by increasing the gas velocity from 35 to 110 meters per second. Dielectric recovery continued after current zero at about 25 volts per centimeter per hundred micro‐seconds, and was nearly independent of gas velocity. A reduction in distance between confining walls from 1.9 cm to 0.635 cm resulted in a one‐third increase of dielectric strength at current zero and a 100 percent increase in rate of recovery subsequent to current zero. Decreasing the arc current from 600 to 200 amperes resulted in a 120 percent increase in dielectric strength at current zero and an eight‐fold increase in subsequent rate of recovery. In various gases, the comparative results for a 600‐ampere arc are given in the table. These results are analyzed from the standpoint of recent theory.

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