Determination of Electrical Breakdown Strength of Insulating Presspapers Used for Power and Distribution Transformers

The performance of an insulation system depends on the degradation of Electrical breakdown strength. Study of their behaviour can gives a useful information regarding the state of the insulation system. The Electrical grade insulating presspapers are obtained from quality cellulose fibers to meet the insulation requirements of motor, capacitor, and transformer manufacturers. Among these, presspapers are mainly used as an insulation for power and distribution transformers. In this paper, the presspapers are prepared by means of water soluble insulating polymers specifically polyvinyl alcohol and povidone (Polyvinylpyrrolidone) and experimental investigations have been carried out to determine the electrical breakdown strength of different grades of insulating presspapers and impregnated presspapers at various temperature of virgin transformer oil and atmospheric air. A system model consisting of presspapers and transformer oil with uniform field electrode arrangement was tested for its behaviour. The system was allowed to age till failure of the sample occurred in the form of a puncture. Series of experiments have performed on presspapers and oil immersed presspapers under laboratory conditions, 40°C and 90°C. Results are then analysed with the view of separately understanding the impact of breakdown strength of insulating presspapers in a transformer.