Partial discharge characteristics of electrical trees prior to breakdown

Electrical treeing is an electrical prebreakdown phenomenon commonly found in solid dielectrics. It is a damaging process due to partial discharge (PD) and progresses through the stressed insulation by chemical degradation whose path resembles the form of a tree root. The characteristics of PDs due to electrical treeing before the insulation breakdown are discussed in this paper. Several point to plane electrode specimens were prepared using epoxy resin as the insulation material, and tested under different voltage levels from 10kV to 12kV AC. While PD data acquisitions were in progress by means of a precision computer-based measuring system, the progress of treeing in the samples was also visually monitored and photos were captured in specific time intervals for each sample. The trends of the phase resolved patterns prior to breakdown and far before breakdown were compared. Also the trends of PD sequences were analysed for critical and non-critical conditions.