Study on dielectric properties of oil-impregnated paper and epoxy/fiberglass composite during DC accelerated ageing

The unqualified properties of interior insulating materials as the main insulation of high voltage DC bushing will affect the operating reliability of bushing. In this paper, two kinds of insulating materials, oil-impregnated paper (OIP) and epoxy/fiberglass (E/F) composite, had been prepared as the typical specimens for present studies. Firstly, the influences of the moisture content in the paper and temperature on the dielectric properties of OIP test were studied. The lab testing setup with DC voltage up to 50kV for DC electrical ageing was established. The main dielectric parameters, including the dielectric loss factor and insulation resistance, of specimens during DC ageing were measured. The relationships between the dielectric properties of specimens and aged duration had been investigated. The infrared spectroscopic analysis and microstructure examination of aged specimens were carried out also. The results show that moisture content within OIP could reflect the dielectric loss factor and insulation resistance effectively. Moreover, compared with un-aged specimens, the microstructures of long-time aged specimens have a significant variation. This study will provide the experimental data and assistances for improving the main insulating materials for high voltage DC bushing application.