Frequency Characteristics of Partial Discharges in Oil-Impregnated PressboardPaper", Paper submitted for

This paper presents the experimental results of the partial discharge activity in oil-impregnated pressboard and paper configurations. Two different configurations were simulated in the laboratory. Both used an aged-sandwiched pressboard with a hole and tracking path in their interfaces. These configurations were modeling air trapped in a void and tracking damage on the insulation. A digital oscilloscope was used to observe the partial discharge waveforms. The partial discharge pattern was recorded using a CDA-3 system. The experimental results showed that the two cases provided different waveforms and PD patterns. These differences in frequency content and in the PD patterns may be associated with the different ionization growths produced by the presence or absence of a metal surface which is able to produce electrons. 1