On partial discharge measurement in dielectric liquids

Partial discharge detection in dielectric liquids requires particular PD measurement techniques and instruments. Simultaneous partial discharge (PD) measurements that are employed on insulating liquids, using dual narrow/wide band detectors, are described. Narrow band PD detectors, which are of the integrating type are suitable for the measurement of the total charge transfer in pC of the overall discharge event. Wide band measurement techniques permit the acquisition of the discrete PD pulses in dielectric liquids, that comprise the overall PD pulse burst signal. These PD pulse bursts are comprised of discrete high frequency pulses of usually ascending magnitude charge transfers. The time position of these pulses within the pulse burst is determined by the times at which the Paschen's minima occur across the expanding cavity due to the small size of the microcavities. In order for them to undergo discharge requires enormously high internal pressures (ca 10 MPa) to ensure a sufficient number of charge carriers. The life duration of these cavities is of the order of several's, with the cavity collapsing, when its size reaches dynamic instability.