60-Cycle AC Breakdown of 345-kV Paper Insulated Cable

High-voltage-time tests at 60 cycles were made with an 800-kV series resonant test set on 21 samples of 345-kV impregnated -paper-insulated high-pressure oil-pipe-type cable. The breakdown level of cables, expressed in equivalent volts per mil for one hour life (V/mil/h) under 200-psig oil pressure decreased from 1130 to 850 V/mil/h when the conductor temperature was increased from 70 to 110°C. At 100 psig the breakdown level decreased from 870 to 670 V/mil/h from 50 to 80°C. One sample at 50 psig with a conductor temperature of 62°C had a breakdown level of 600 V/mil/h. Fault paths terminated in radial holes at the conductor and outer shield with a longitudinal running path between these terminations. There was no regular pattern to the fault paths, relative to the conductor screen or to gaps between turns of the insulating tapes.