Abstract
Summary form only given. The present issue of the IEEE Transactions on Dielectric and Electrical Insulation is principally devoted to papers dealing with dielectric liquids. The subject is of great importance in the electrical insulation area, because insulating liquids are extensively used in the area of liquid filled power apparatus such as transformers and capacitors. Over the past decade there have been considerable efforts to improve the electrical and thermal properties of existing liquid dielectrics as well as to introduce new dielectric liquids with better insulating properties as well as develop improved testing methods for their evaluation. The opening paper in this issue is of a tutorial nature and addresses the development of standards for partial discharge (PD) measurements on dielectric liquids. Such information should be useful for standards oriented organizations that are currently engaged in the preparation of testing methods for PD detection and measurement on insulating liquids. In many respects partial discharges in insulating liquids must be viewed as a precursor stage of breakdown streamers in these liquids. The latter have received much attention in the past and continue to sustain interest in studies dealing with the mechanism of breakdown in dielectric liquids. Over the past decade there has been considerable effort directed towards researching the effects of copper sulfide in mineral oils. The problem gained attention when a significant number of transformers and reactors, that had undergone failure, were found to contain corrosive sulphur in their mineral oil. Subsequent research and testing of these oils indicated that they contained corrosive sulphur, which after its reaction with copper conductors gave rise to the formation of semi-conducting copper sulfide, resulting in overheating and the further formation of hot spots. Thereafter the work volume on this subject diminished considerably, as is evident in the present issue. Finally, mention should be made of the natural and synthetic esters, which are now being used in transformers. They have received considerable attention, because both types of esters are biodegradable and thus benign to the environment. Their electrical properties are found to be comparable to those of mineral oils. Both types of liquids are principally used primarily in distribution transformers. Evidently, the number of published papers in the Special Issue on Dielectric Liquids reflects the activity in this field of endeavor. It is surprising that in the past issues on Dielectric Liquids, the number of papers published tended to hover in the vicinity of 20, as it also does in the present issue. The tentative date of the next Special Issue on Dielectric Liquids is planned four years hence.
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