Investigation of Particle Initiated Partial Discharges in Transformer Oil with Pressboard Barrier Under Divergent Fields

Abstract

Particle initiated partial discharge (PD) in oil is one of the significant problem associated with transformer. Among particles, conductive particles play very detrimental role. The existence of conducting particles is very difficult to avoid completely during the manufacturing process and also it can be developed during service period of the transformer. These free conductive particles can adhere to paper or pressboard insulation barrier or freely move in the bulk oil. In transformers divergent (non-uniform) fields are often present due to the geometry of the internal parts and may be due to sharp points. Therefore to understand and characterize the effect of conducting particle in oil with pressboard barrier under divergent fields are very critical for the life assessment of transformer. Sphere-plane and needle-plane electrodes are used to generate different non-uniform fields. The discharge measurements are carried out using partial discharge measurement technique according to IEC 60270. Phase resolved partial discharge (PRPD) pattern, discharge characteristics such as average and peak discharge magnitude, number of discharges per cycle, discharge power, rise and duration time of PD pulse due to conducting particle in oil with pressboard barrier under divergent fields are analyzed. The observed PRPD pattern were relatively similar regardless of applied divergent fields. The observed PD inception is much earlier in quasi uniform field compare to non-uniform filed, the PD inception voltage (PDIV) in non-uniform field is three times higher than that occur at quasi-uniform field.