PDC and PD Pulse Burst Characteristics in differently aged Transformer Oils

PDC (polarization/depolarization) and PD (partial discharge) characteristics of three typical transformer oils, having differently aged level, were examined using PDC test and PD test under AC conditions. PDC test shows that with the aging level increased that impurity density and conductance of oil is increased, the bound charge in oil wills more and more. Partial discharges, which take place in insulating oils for electric field concentration, appear in the form of pulse bursts that consist of a series of discrete current pulses. The first pulse of pulse burst is due to the initial streamer in the liquid phase, and all subsequent pulses will be the PD pulse responses in the growing cavity. The time interval between the first and second pulses is the form time of cavity. The number of pulse within burst as function of voltage and time interval between first and second discrete pulses within the PD pulse burst as a function of voltage are studied in this paper.