Abridgment of circuit breaker recovery voltages: Magnitudes and rates of rise

Abstract

This paper shows the conditions affecting the magnitude and rate of rise of recovery voltage at the terminals of an oil circuit breaker upon interruption of a short circuit; also explaining their effect in quantitative terms. The most common locations, and a rough idea of the magnitude of the capacitances affecting the rate of rise of recovery voltage for various types of short circuit, are indicated, and calculations of the recovery voltage curve for several representative cases at both low and high voltages are presented. In some cases cathode ray oscillograms are given for comparison with the calculated curves. While at present no systematic data regarding the effect of the rate of recovery voltage rise upon circuit breaker operation appear to be available, several tests showing a very pronounced effect — some of them made by the authors and some by others — are reported briefly. There are presented factors whose numerical value lakes into account: the number of phases involved in the short circuit and the ground connections of short circuit and generator; the decrement of short-circuit current previous to interruption, and the effect of unequal reactances in the direct and quadrature axes of synchronous machines. The paper also indicates how one may calculate the effect of displacement and initial load current, besides briefly discussing the effect of saturation. Magnetic oscillograms to verify the most important of the points brought out are shown. A discussion of the method by which overvoltages are built up during the interruption of transmission line charging currents is presented at the end of the paper.