The Quality Rating of High-Tension Cable With Impregnated-Paper Insulation

During the past five or six years, practically all of the American cable manufacturers have made some changes in their impregnating compound so as to produce cable having a low dielectric loss. In a number of cases, these compounds were not well chosen. During the same period, some of the operating companies have reduced the thickness of their insulation, resulting in increased dielectric stresses. In a number of cases, the compounds and perhaps also the paper that was used developed faults that were more serious than high dielectric loss. Some cables have been very deficient in dielectric strength and others have developed a new type of trouble which has been termed ``ionization´´ and, after a comparatively short time, the operating voltage of such cable had to be materially reduced in order to keep the lines in service or the cable had to be replaced. The cable manufactured during this period has generally passed, with a wide margin, the high voltage tests required by the specification. Occasionally a lot of cable which passes these tests by a narrow margin will be shipped by a manufacturer and, in such cases, the service record of the cable is unsatisfactory. The investigations which form the basis of this paper consist of: (a) Laboratory tests to determine what high-voltage tests cable known to be of good quality will withstand as well as the similar tests on other grades of cable.