1 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
to discuss PD mechanisms based on physics, in this paper, we
developed a useful PD measurement and analysis technique
referred to as "PD Current Pulse Waveform Analysis (PDCPWA)".
PD-CPWA can obtain not only individual PD
current pulse waveforms with the time resolution of the order
of sub-nanoseconds, but also its time transition from PD
inception to BD, with the PD detection sensitivity of 0.1 pC.
The obtained PD current pulse waveforms can also be
analyzed in terms of different parameters such as peak value,
di/dt, rise time, fall time of a single PD pulse, time interval of
subsequent PD pulses and so on. This paper introduces the
concept, principle and applications of PD-CPWA to PD
characteristics in solid, liquid and gas media under ac voltage
application.