Initiation and formation of partial discharges (PD) in mineral based insulating oil

The authors report the results of fundamental investigations concerning the behavior of partial discharges (PD) in mineral-based oil with the aim of characterizing the physical mechanisms that lead to the initiation and formation of PD pulses. The influence of temperature, moisture, and pressure on the PD inception voltage, the apparent charge, and the number of PD pulses is studied. In addition, results obtained by investigating the shape of PD pulses and the behavior of visible PD channels using the schlieren method are explained. The results show that the PD process in mineral-based insulating oil can be divided into several independent physical processes, each characterized by different PD parameters