However, in order to elucidate physical mechanisms of PD
inception and propagation, the individual PD current pulse
should be discussed in detail [6]. Time-resolved PD
characteristics, i.e. PD current pulse waveform as shown in
Figure 2 for (a) N2gas, (b) SF6gas and (c) transformer oil,
respectively, will give us much more information based on the
physical PD mechanisms. In other words, PD current pulse
waveforms may tell us their physics.
Figure 1 shows typical phase-resolved PD characteristics (φ-q characteristics) of (a) air and (b) SF6gas, respectively, for a
needle-plane electrode system. Such phase-resolved PD
characteristics allow us to discuss statistical PD characteristics
and have contributed to identify the type of defects in the
insulating media from the viewpoint of the pattern recognition
technique.