Measurement of partial discharges in hexane under DC voltage

Partial discharges are recorded by means of high-magnification, high-speed photography in effort to determine the relationship between the growth of the partial discharge and the current supplied to produce it. A needle-sphere electrode geometry is used to observe partial discharges at the tip of the needle for both positive and negative DC polarities. Observations of the initiation phase of the partial discharges are accomplished by the use of an image-preserving optical delay that permits photography of fast events. The current is monitored by a low-noise amplifier that also provides timing signals to operate the photographic system. The partial discharges are found to closely resemble the structure and growth of the slowest (subsonic) cathode events emanating from a tip under the application of negative impulse voltages. With DC, the current producing the partial discharge is in the form of a pulse train, which is in contrast to the linear growth observed in the streamer. >