Size effect of partial discharge in solid void defects

The void defect in solid insulation can be considered as one of the important defects which will induce partial discharges (PD) and insulation degradation. In this paper, the relations between the cylindrical void size and PD characteristics are presented and summarized particularly. The PD inceptive electrical field (PDIE), the maximal PD magnitude and the impulse waveforms are especially studied with different void defects' depths and diameters. These PD characteristics, especially for PD impulse waveforms, changed dramatically with the increase of void size, which imply the various ionization states in PD process. The results show that large size voids always induce low PDIE and large maximal PD magnitude, which confirm the certain relations between insulation degradation degree and PD characteristics. Some of the results show that the PD with more residual ions may cause much serious degradation of solid insulations. The floating electrode defect test has been designed as a proving trial lastly.