The influence of moisture on the insulation performance of epoxy resin impregnated paper

Dampness is one of the common failures of epoxy Resin Impregnated Paper (RIP) bushings. In order to study the influence of moisture on the insulation performance of RIP bushing, samples were made by cutting from the actual bushing. The moisture content was measured with a precise moisture tester which can dry and weigh the samples. The dielectric loss factor (tanδ), insulation resistance, dielectric absorption ratio, frequency domain dielectric spectrum and other parameters of the sample with different moisture content were measured in a three electrode system. The test results indicate that the insulation resistance and dielectric absorption ratio of the sample both decreases with the increase of moisture content. When the moisture content is less than 0.67%, the dielectric absorption ratio is above 1.5. The dielectric loss factor and the relative permittivity of the sample increase exponentially with the increase of the moisture content. The measurement results of frequency domain dielectric spectrum show that the tanδ in 1Hz-100Hz frequency band is more sensitive to the moisture content of the sample piece. When the moisture content is lower than 0.5%, the tanδ -f curve shows a V-shaped change trend in this frequency band, and the inflection point appears at 10Hz. The relationship between integral value of tanδ-f curve and moisture content can also be expressed by exponential function. And the real part of complex permittivity increases with the increasing of moisture content but decreases with the frequency increasing. The research results can provide reference for RIP bushing insulation diagnosis and operation maintenance.