Practical Calculation of Electrical Transient on Power Systems

Solution of many power-circuit problems depends upon the magnitude, duration, and frequency of occurrence of transient voltages and currents produced by circuit changes. Circuit-opening or recovery-voltage transients are fundamental in the operation of interrupting devices and may be important from the standpoint of the dielectric strength of circuit elements. Circuitclosing transients may be important from the standpoint of inrush currents and occasionally from the standpoint of overvoltages. Both types of transients may be increased greatly if restriking and repetitive interruptions take place. Transient voltages and currents resulting from circuit changes can be calculated by the classical method with the aid of differential equations or by the Heaviside method, particularly with the aid of the expansion theorem. Transients on complicated power systems are most conveniently determined by the miniature-system method introduced by Evans and Monteith and described in their 1937 AIEE paper.⁴ Analytical methods are useful for simple problems and are essential for those beyond the range of the a-c network calculator or when it is not available. Analytical methods are also necessary for determining the proper form of the equivalent networks for the representation of power systems on the a-c network calculator. This circumstance provided the occasion for the particular investigation for which the present paper is a partial report. This paper is devoted to the practical calculation of power-system transients and presents concepts, methods, and approximations selected with that objective in view. The paper describes a method of calculation particularly adapted for engineering work.