The Geometry of Arc InterruptionߞII Current-Zero Phenomena

During the microsecond period in which an interrupter is performing the act of changing from a conductor to an insulator (termed interruption) the current, voltage, and arc resistance undergo variations which materially affect the performance characteristics of the interrupter. The nature of these variations depends upon the medium of interruption design features of the interrupter, and the constants of the current and recovery-voltage circuits. Modern power interrupters employing air present variations in the current-zero region of an entirely different type from that observed in the fluid interrupters. A knowledge of the nature and cause of these variations is becoming of more importance from a design performance and application viewpoint. The rapidly varying resistances within the interrupter during the process of interruption have always presented obstacles to the analyst. In reapproaching this problem on the basis of an orderly, yet practical, variation of circuit current in the region of current zero and allowing the parameter of resistance to become secondary, the problem reduces to one of linear constants and can be solved by standard methods. This paper presents such a treatment. It is generalized in such a way as to include all practical types of current-zero phenomena generally encountered. Recovery-voltage characteristics are literally fabricated from "standard building blocks" of which relatively few are required. The method is flexible enough to be applied to any assumed current variation in the region of current zero. The analysis is presented in terms of the accepted nomenclature of circuit theory. The operational attack is employed.