Electrical Insulation Properties of Polyvinyl Formal Wire in Mineral Oil Under Thermal and Electrical Accelerated Aging

Abstract

This paper deals with partial discharge inception voltage (PDIV) and long-term voltage-time (V-t) characteristics of Polyvinyl Formal (PVF) wires in mineral oil under thermal and electrical aging. The reliability of the long-term insulation performance was evaluated considering the thermal aging of PVF wire and the aging due to humidification of the insulating oil. The results showed that PDIV decreases with an increase in the temperature of heat treatment in the oil. It was also found that the lifetime of specimens subjected to the thermal aging up to 180°C was reduced compared to that of non-treated specimens. In order to examine the reduction in the long-term charge life of thermally aged specimens, chemical analysis was performed using a Fourier transform infrared spectrometer (FT-IR). The results suggest that the decrease in the long-term voltage application lifetime of the thermally aged specimens is caused by the low molecular weight of the PVF wire coating due to thermal aging. From the above experimental results and discussion, it was concluded that the PVF wire thermally aged at 180°C for 2 months, which corresponds to 60 years of operation according to the 10°C half-life law, maintains sufficient insulation performance at 1 kV stressed to the coatings and can be expected to have a service life of more than 30 years.