Characteristic properties of oil-impregnated laminated synthetic insulation for extra-high-voltage cables

In the paper a review is given of the properties of oil-impregnated lapped-plastic-tape dielectrics for use as insulation in extra-high-voltage underground cables. The following subjects are discussed: choice of combinable materials, impregnation technique, results of breakdown measurements as a function of various different parameters, dielectric-loss measurements and thermal conductivity, it appears that a cable insulation with a breakdown strength 80% higher than that of oil-impregnated-paper insulation is technically possible. The new insulation, consisting of film tapes of polyphenylene oxide impregnated with paraffinic oil, has a dissipation factor more than five times smaller than that of conventional oil-impregnated paper. in cables with such an insulation, operating stresses of 15¿37kv/mm, depending on tape thickness and pressure, may be applied.