Partial-discharge activity for a negative DC corona in atmospheric SF6

Partial discharges were investigated under negative true-corona conditions. A plane/point/plane geometry was used, allowing for a reasonable voltage span of the I-V characteristic when DC was applied. The pressure of the SF₆ gas, 800 Torr, and the order of magnitude of the applied voltage 25 kV feature conditions found in distribution systems. Pulse activity was observed and recorded as a function of applied voltage. Sampling of a large number of pulses was used to define distributions of the pulse amplitudes and pulse frequencies. These distributions exhibit varying features with increasing applied voltage. The present findings, plus the observed temporal variation of some of the measured corona characteristics, illustrate some potential drawbacks suffered by pattern-recognition approaches applied to varying-field conditions