INTRODUCTION
FOR the insulation diagnosis of electrical insulating materials
in high-voltage power apparatus, partial discharge (PD)
measurement has been recognized as an important tool [1].
However, physical mechanisms from PD inception to
breakdown (BD) have not been well understood [2, 3]. Future
PD measurement should be based on the physical mechanisms
of PD inception, propagation, degradation and BD of the
materials, which will contribute to the reliable insulation
diagnosis of high-voltage power apparatus.
Since PD signals are so faint and have the frequency
component as high as the order of GHz [4], PD measurement
in electrical insulating materials is very difficult. PD
mechanisms are also quite complicated, since they depend on
different physical and chemical parameters. However, the PD
measurement should be reflected in their physics and then in
their current pulse waveforms. The reason is that the rise and
fall times of a PD current pulse waveform are directly
determined by electron avalanche and/or streamer/leader
discharge extension, and by diffusion and recombination of
charge carriers, etc. [5].
From the above viewpoints, we have been investigating PD
characteristics and mechanisms of different insulating
materials such as gases, liquids and solids. As an effective tool