Corona discharge currents of a point plane air gap: Spectroscopic studies and effects of silicone rubber

This paper describes results of measurements made using modern digital instrumentation to simultaneously record current pulses and visible images associated with corona discharges in a 8.255 mm point-plane gap in atmospheric air with 50 Hz applied voltages up to flashover. Discharge current pulses are recorded at a sampling rate of 200 mega samples per second by a digital oscilloscope with an estimated 14 nsec time constant for the total measuring circuitry. The effect of a 0.2 mm sheet of silicone rubber insulation placed over the surface of the plane electrode is also examined. Analysis of the current measurements provides new information about the formation of pulses particularly double-peaked types observed only occasionally by previous researchers. Photographs from a digital camera with extended UV capability show images of the corona produced for each type of discharge and atomic emission spectra of the corona are obtained up to and including spark-over with a high resolution digital spectrometer with a fiber optic probe, for wavelengths from 200 nm to 1100 nm with an accuracy of ±0.25 nm.