Electrical properties of vegetable oil-impregnated paper insulation

This contribution presents results from testing electrical properties of transformer paper-insulation with vegetable oil as paper impregnant. Investigations have been made with two kinds of typically used pressboard materials in power transformers. More precise, pressboards of type T I and T IV manufactured by Weidmann Transformerboard Systems AG were impregnated with an oxidation resistant biodegradable rape-seed oil. Tests included determination of power-frequency voltage strength according to IEC 641 and dielectric dissipation factor according to IEC 250 of the impregnated pressboards. Moreover, in order to shed light on the effect of ageing on electrical properties investigations with thermally stressed boards have been carried out. Therefore, 4 weeks oxidation period at 120°C temperature of specimen was used. Obtained results are compared to additional tests of pressboard impregnated with conventional transformer oil Shell Diala D. The investigations establish possibilities of using environmental friendly rape-seed oil for transformer applications.