The Mean or Maximum Stress Theory: Possible Solution of an Old Dilemma

Ever since the application of cables for high voltages there has been a distinct difference in European and American practice for designing the dielectric. In Europe the design is based on the assumption that the maximum field strength (i.e., the stress at the conductor) determines the breakdown of the cable; in American practice the mean field strength throughout the dielectric is taken as the determining factor. Recently a Japanese paper on the design of oil-filled cable showed that the European practice should be extended by introducing a correction factor to provide for a broad field of conductor sizes and insulation thicknesses.