The electrical and dielectrical behaviour of mixed insulation liquids for transformers

In this paper the main results from investigations aiming into the retrofilling conditions of a Transclene (perchlorethylene based liquid) filled transformer are presented. The investigations are carried out on insulating liquids with less environmental risks than perchlorethylene (Perc) but of almost similar electrical properties which are a mineral based transformer oil, a synthetic ester liquid and a synthetic silicone liquid. Also the influence of a small detachment of hydrochloric acid (HCl), which can be generated by the Perc during operation is discussed. A comparison of the measured data with the predeterminations of the relevant standards and the consequences for the use of the mixtures in transformers are presented