Stability of Electrical-Insulating Oils

Knowing that oil is a weak link in a composite or impregnated dielectric system with reference to both dielectric strength and ease of contamination, many investigators have devoted great efforts to try to ascertain the best types of oil for various operating conditions. However, different investigators seem to have different opinions as to the best-suited type of oil for this purpose. It is the object of this study to involve a wide variety of oils and test conditions to shed some light on this controversy. Ten original oils and three blended samples selected from an array of over 50 original specimens tested have been chosen to illustrate the tenacity of this problem. The samples include both mineral and synthetic oils, coming from domestic sources as well as from abroad. Their sources or ethnic groupings seem to indicate no preference, but the care in refining these samples seems to be a factor. In this investigation, two criteria have been chosen to indicate the service quality of the oils: gas-absorption and liberation characteristics and electrical deterioration under moderate electrical stress. In the presence of carbon dioxide, no oil has been found to liberate gases. In the presence of air, nitrogen, or oxygen, although gas liberation has been observed in some of the European oils at some stages of aging, there has been no sharp rise in dissipation factor or indication of internal discharge or failure.