Partial Discharges Behaviors of Internal Void in the Oil-Paper Insulation and its Effect on the Material

Because of the complexity of transformers construction, internal voids in the insulation seems inevitable when fabricating, which would cause partial discharge (PD). Therefore,it is of great significance to monitor the PD to study in which condition the PD will make the insulation degradation and whether there have diversities among different PDs. In this paper, the oil-immersed paper samples are artificially thermally aged to obtain specimen with different aging states, and the continuous test on oil impregnated paper with internal void defect are developed and the phase resolved partial discharge (PRPD) pattern of PD signals during the electrical aging process are measured. The experimental results show that the PD behaviors in internal void of the oil-paper insulation have couples of transient processes and the mechanisms behind are quite complicated. The pulse sequence analysis results validate that thermally aging condition of paper have great impact on PD characteristics, which show that the pulse number increase and time between consequence discharge get closer. The study would be helpful to possibly determine the discharge type and condition assessment of power transformer with the PD monitor.