The measurement of gas produced by electrical power arcs in insulating oil

Abstract

This thesis presents a study of the factors which influence the gas rate (volume of gas produced per unit arc energy) in insulating oil. Such data are fundamental to the design of oil circuit breakers. It is found that the gas rate varies with electrode length, location of arc on the surface, duration of current and material of arcing surface. The gas rate is higher for the longer gap length (3/4 inch) than for the shorter gap length (1/4 inch). An arc on the center of the surface generally gives a lower gas rate while that on the edge a higher gas rate. For arcs occurring on the center, copper surface has a higher gas rate while steel and silver elkalite (alloy used in practice) surfaces have approximately the same lower rate. A high gas rate results in the short duration arc of 1/2 cycle and nearly equal low gas rates are obtained for durations of 2 cycles and 3 1/2 cycles. No appreciable change in gas rate is observed as the magnitude of current peak varies from 400 to 800 amperes. With the method used in this research, steel surfaces have the desired character that arcs always occur on the center. For 600 amperes and 2 cycle duration, the gas rate of flat steel surfaces referred to 760 mm and 25[degrees]C is 74, 133 and 175 cubic centimeters per kilowatt second at 1/4, 1/2 and 3/4 inch gap lengths respectively. Because the gas rate for silver elkalite and steel surfaces are about the same with arcs on the center, the effect of current magnitude is small and the arc duration in most circuit breaker operation about 2 cycles, the total volume of gas produced in actual operation of a circuit breaker can be calculated approximately by correlating the above figures with field test records of arc energy and electrode travel.