A Comparison of Arc Characteristics in Switching in Vacuum and in Oil

This thesis describes the results of an investigation of the arc end glow discharges occurring between the contacts when an alternating current is interrupted by an oil circuit breaker; and a comparison with similar phenomena in the vacuum circuit breaker is made. This investigation was made by taking cathode-ray oscillograms of the variation of voltage across the contacts, and the current through the discharge, with time, and the variation of the voltage across the contacts with the current through the discharge. Circuit voltages of 15,000 and 2300 were used, and currents up to 45 amperes were interrupted. The discharges across the separating contacts of an oil circuit breaker are discussed in detail, and an analysis of the variations near the zero of the current wave is made. This investigation shows that for a brief period, of the order of 300 microseconds, at the end of each half cycle of the current wave the current between the contacts is of a very small magnitude, and may be considered essentially zero. During this interval the voltage completes a part of an oscillation, the frequency of which is apparently determined by the constants of the connected circuit, and rises in the reverse direction until a certain maximum is reached. After this value is reached current again flows end the usual glow and arc phenomena are observed.