Power-System Transients Caused by Switching and Faults

Abstract

This paper summarizes the results of an investigation of transient voltages on power systems caused by switching and faults. The transient voltages on power systems as measured by the “klydonograph” are reviewed and compared with the flash-over values of transmission-line insulation. It is shown that the higher values of transient voltages are produced by intermittent arcs. In part I, the various theories for the production of transient voltages of high magnitude as a result of intermittent arcs are reviewed and extended in order to obtain the highest voltages on typical polyphase systems with the range of natural frequencies and attenuation factors that are encountered in practice. Previous studies are of limited scope and apply principally to the case of an arcing ground on an ungrounded system. The present study shows broadly the range of transient voltages which may be produced with intermittent arcs and applies to switching operations as well as arcing grounds. A typical transmission system is studied with the aid of the a-c network calculator. One of the principal variable factors in this study is the method of system grounding and this includes a range of both resistance and reactance between the limits of a solidly grounded system and an ungrounded system. The study is carried out for four different conditions, namely: (1) arcing grounds, (2) de-energizing an unfaulted line section, (3) de-energizing a line section with a fault on one phase, and (4) de-energizing a line section with a fault on two phases. The results of this study are presented in graphical form in part II and show many interesting properties of systems with respect to the method of grounding, and the characteristics of transient voltages for the different switching and fault conditions. It is the authors' opinion that the transient voltages due to. faults and switching deserve more attention than they have received within the last few years.