Effect of Non-conducting Particle in Transformer Oil Partial Discharge Characteristics

This paper investigates, the effect of non-conducting particle in transformer oil partial discharge (PD) characteristics with quasi-uniform field under applied AC voltage. Non-conducting particle such as cellulose fibre from paper or pressboard were used to study the PD characteristics. The cellulose fibre is hydroscopic and absorbs water very quickly. The cellulose fibre having very high affinity to draw water from oil at room temperature. Once the cellulose fibre become wet, the conductivity and permittivity may increase, it can significantly affect the insulation performance of the oil. Dryness of the cellulose fibre greatly depend on the temperature and drying condition. Therefore the cellulose fibre from pressboard dried in an oven at temperature of 105 degrees C for 1 h, 2 h, 4 h and 6 h were used to study the effect of cellulose fibre in oil with different dry conditions. The cellulose fibre without drying is also used to study the wet condition. PD detection according to IEC 60270 was employed to understand the effect of non-conducting particle on transformer oil PD characteristics under quasi-uniform field. The phase resolved PD (PRPD) pattern, PD characteristics such as magnitude, number, discharge power, rise and duration time were analysed. The observed PRPD pattern began from 45 degrees and 225 degrees phase of applied AC cycle, further increase of voltage can enhance the appearance of PD throughout the phase, and patterns are similar trend regardless of the wet conditions of cellulose fibre. The observed PDIV is close for each dry conditions of cellulose fibre whereas discharge magnitude has significant variation.