Operating Performance of a Petersen Earth Coil-II

At the A. I. E. E. Spring Convention, Pittsburg, April 24-26, 1923, a paper was presented by the authors on the operation of a Petersen earth coil installed by the Alabama Power Company on its Lock 12-Vida 44,000-volt system. That paper reported an excellent performance record for the coil, although several unaccounted-for bus insulator flashovers occurred at Lock 12, indicating that further investigations on the action of the coil were necessary. This paper presents eleven months´ additional operating experience with the Earth Coil, which shows that over-voltage disturbances can be eliminated by doing all line switching operations with the Petersen Coil out of service, that is, with the system neutral solidly grounded. It is believed that the same results can also be obtained by under-tuning the coil. The Lock 12 Coil is no longer in service, as the system has out-grown the need of such equipment; additional power sources have been added to the system and reliable service can be maintained without the use of flashover suppressing devices. It appears that the application of Petersen Earth Coils is limited to comparatively low voltage lines (66,000 volts and less) of moderate length with a single source of power supply. In such an application, the use of a Petersen Coil between system neutral and ground has the advantage over grounded neutral operation by reducing line outages due to flashovers and over isolated neutral operation by eliminating arcing grounds.