Dielectric and Microstructural Deterioration Process of Resin-Impregnated Paper Materials Under Electrical-Thermal Combined Stress

Resin-impregnated paper (RIP) have been widely employed as main insulation material in high voltage transmission apparatus, in which intensive electrical-thermal combined stress may lead to considerable material deterioration and even insulation failure during long-term operation. However, a comprehensive investigation on the deterioration process of the material under the combined stress has been absent so far. In this paper, different conditions of electrical-thermal degradation were conducted on RIP material samples, during which main functional group and the frequency domain dielectric response were measured to characterize the deterioration process. It is found that under continuous electric-thermal stress, molecular chains within the material degrade and this leads to continuous generation of small molecular substances. Particularly, the material shows a decrease in ether bonds and an increase in hydroxyl groups. Also generation of gas products accumulate as bubbles on the epoxy-paper interface which results in interface delamination and making the interface a weak point. Meanwhile, the dielectric constant and dielectric loss of RIP increase continuously, indicating considerably intensified orientation polarization and interface polarization, which agrees will with the evolution property of the functional groups. Furthermore, the relaxation time and intensity were obtained from the dielectric response of the material and were fitted with the degradation time, which can serve as a good indication of the deterioration degree and type of the RIP material.