A Study of the Behavior of a Uniaxially Oriented Polyethymene Tape/Oil Insulating System Subjected to Electrical and Thermal Stresses

The occurrence of discharges in an insulation system consisting of lapped uniaxially oriented polyethylene tapes impregnated with dodecylbenzene oil and the behavior of air bubbles injected into the structure have been investigated. This insulation system should be suitable for use in power transmission cables because the tape is generally compatible with the oil and has suitable mechanical properties for cable manufacture in a conventional cable taping machine. The behavior of bubbles in the systems was monitored with a transparent electrode and a video system. An electronic protection system was used to remove the applied voltage just before breakdown so that the damage done by discharges to the tape structure could be measured. The discharge inception voltage was found to decrease with increasing butt gap depth and with increasing temperature. Bubbles were found to divide repeatedly and eventually to disperse at stresses above discharge inception. The rate of dispersal increased with increasing applied stress and temperature. Examination of the damage done to tapes showed a high level of correlation between the total energy of discharges in the insulation structure and the total surface area of visible damage. Measurement of the total discharge energy appears to be a promising diagnostic tool.