A Study of High-Voltage Flashovers

A brief discussion is given of the various forms of electrical discharges as they are characterized by the physicists. Oscillographic records secured of voltages and currents, both before and during the flashovers, are reproduced and discussed. Polarity tests are described in which the electrode shape and spacing were found to determine the sign of the half-cycle at which flashovers would start. Photographic results obtained with moving films are illustrated, showing the various stages of a flashover from the formation of the corona discharges, through the initial sparkover, to the development of the half-cycle arc channels. The flashovers studied ranged from several feet to 22 ft. in length. Spectrographic analyses of the different stages of a flashover are described, wherein it is possible to gain some knowledge of several of the factors contributing to the conductivities of the various stages. Several of the spectra obtained are illustrated along with a comparison spectrum of lightning. With the knowledge gained from the laboratory studies made, the probable history of a high-voltage a-c. flashover is summarized.