Radial Electric Field Distribution in an Aged Paper Insulated AC Cable

Paper insulated cables were the first commercially used cables and they continue to be in service even today owing to their long history of reliability. Under repeated load cycling and varying electric stress and temperature, however, the dielectric properties of the cable undergo changes. In this work, the relative permittivity of paper insulation from a used and aged oil impregnated paper cable has been measured at different electric fields and temperatures using dielectric spectroscopy. Electric field along the radius of the cable has been obtained using a software based on finite element method. The results obtained through dielectric spectroscopy have been used to input the properties of the cable paper insulation in the software. A comparison of the radial electric field distribution inside the paper cable has been made for two cases; one where the relative permittivity of insulation is dependent on temperature and electric field and the other where it is independent. The results of this work may prove to be useful for monitoring of ageing cables and for cable joints involving paper cables.