An analysis of transient and sustained voltages in ground-fault neutralizer systems

THE first ground-fault neutralizer (Petersen coil) in the United States was installed on the Alabama Power Company system in 1921. The technical press at that time devoted considerable attention to the substantial improvement in service continuity which was obtained with the neutralizer, and also described the overvoltages which occurred on the system during switching operations.¹ Since this first application, more than fifty ground-fault neutralizers have been installed on systems in the United States in all voltage classes from 22 kv to 230 kv. Considering the total number of neutralizer-years of successful operating experience that have now been accumulated, it can therefore be stated that the ground-fault neutralizer has definitely proved its value as a service protective device, and that practical means have been found to eliminate the overvoltage troubles encountered in the first application. The very favorable operating record obtained to date indicates that ground-fault neutralizers may be expected to find increasingly widespread application in the future.^2,3,4,5 The question of overvoltages, however, is still raised from time to time with reference to prospective applications of ground-fault neutralizers, presumably because of the attention which the overvoltage problem has received in the past,^6,7,8,9,10 and it is felt that an analysis of the possible causes of and the means used to control overvoltages is in order. It is the specific purpose of this paper, therefore, to present data to indicate possible sources of overvoltages in ground-fault neutralizer systems, to point out the factors affecting the voltage magnitudes, and to show how the overvoltages are limited by present design and application practices.