Empirical equations for the 60-cycle spark-over gradients in commercial oil

INTENSIVE experimental work on dielectric phenomena in liquids has been done during the last 40 years. There is considerable interest on the engineer's part in obtaining reliable information about the dielectric properties of liquids, especially of commercial oil, used as insulation and as a cooling medium for transformers, circuit breakers and much other electrical apparatus. Many valuable experimental results have been obtained for dielectric strength, corona, dielectric losses and other dielectric properties of commercial oil.1‾5 In connection with the first-mentioned problem, that of the dielectric strength or oil, numerous details have been carefully studied: for example, the influence of electrode geometry, the rate of voltage rise, humidity, dissolved gases and different kinds of contamination. However, as Whitehead has mentioned,6 “Breakdown in liquids could readily become a compendium of unrelated observations” because very little was known about the physical background of this field.