Dielektric Response in Oil-Paper Insulation

Abstract

Transformer insulation consists mainly of oil and paper. Moisture in the paper adds a significant contribution to ageing of the insulation system. It is therefore of great importance to know the moisture content.A method to measure this is dielectric response performed on the transformer terminals. This is a fast procedure and can save equipment from failure. In order to identify moisture content from dielectric response there is a need for a better understanding of the dielectric response of the insulation.A watertight Teflon cell is used to measure dielectric response on different paper insulation in this thesis. The response is measured at frequencies from 10 Hz to 4 MHz. This is a relatively low specter in dielectric response and will give detail on the conductivity level in the papers.Three hypotheses about the variables are investigated.- Conductivity is dependent on moisture content and measureable for low frequencies.- Dielectric response of paper is independent of oil impregnation.- Conductivity is dependent on paper density.The conductivity is strongly dependent on the moisture level and it should be possible to gain knowledge of the moisture level from dielectric response tests.The oil impregnation seems to have an impact on the conductivity in the low frequency area. The oil makes the conductivity rise a little in the paper but it seems very predictable and it should be possible to adjust for this variable.The density of the papers has lower contribution to the response than both the oil and the humidity. To get more understanding of the density contribution there needs to be done more tests on oil impregnated paper at equal humidity but different densities.