Relationships of corona to life and reliability of polyethylene insulated cable — New test methods for cable

Life data have been used to test the merits of methods for estimating life from corona measurements on unaged cable and to determine the significance of corona specifications. Required life is generally 1011 cycles of applied voltage. Life with corona is 7×108 cycles or less. Without corona, life is 1011 cycles even at extreme voltage stress. Radio-frequency cable may be used wherever required life is less than 108 cycles and voltage is below twice the corona starting voltage if materials and processing are in control. Such control is demonstrated in the results of a 1-day 60-cycle life test. Then, expected life is predicted from corona data assuming that the number of corona discharges to failure is constant. The effects of temperature, frequency, voltage, materials, fault types, and cable construction are described. The statistics of cable life are discussed.