Progress in the field of electric properties of dielectric liquids

It is noted that the past three decades have seen significant changes in the types of materials used for electrical insulation. These changes were brought about by the realization that some of the previously used materials were detrimental to the environment and to the people who came in contact with them. The use of polychlorinated biphenyls was prohibited, and replacement materials had to be developed. Paper was replaced to a large extent by polymer film, and paraffinic oils were finally used as replacement for oils derived from naphthene. At the same time progress was made in the understanding of the nature of electrical charges and how they move through dielectric fluids under the influence of externally applied electrical fields. The impact of these developments on the field of liquid insulating materials is discussed. Attention is also given to the information obtained with the latest ultra-high-speed electrooptical equipment. The generation and propagation of charge carriers are examined in detail, and their relation to electrical breakdown is analyzed. A brief survey of the special instruments used in these studies is presented, and the advantages and disadvantages of the various measuring techniques are discussed