The real time and statistical characteristics of waveforms from partial discharges in dielectrics

Real time waveforms and their statistical properties help to identify and characterize differences in the partial discharge processes that cause them. A special test cell has been constructed which permits simultaneous observation of both the electromagnetic and the ultrasonic signals generated by partial discharges in dielectrics. A basic cross section of the test cell is shown in Fig. 1. Different inserts can be employed to study the effects of different materials and electrical configurations. Considerable effort was expended in the design of the cell and associated apparatus so as to preserve the waveform shapes as well as feasible. The electromagnetic signals are processed in circuits with bandwidths of tens of megahertz. The ultrasonic transducer and circuits have a bandwidth of tens of kilohertz centered about frequencies of hundreds of kilohertz. Auxilliary digital processing allows the selection of particular types of digital waveforms for statistical studies of such features as time between discharges, discharge energy, and phase relationship to the excitation voltage, for example.