Study and analysis of field enhancement and H.V rating of power cables containing micro cavities

Partial discharge (P.D.) in micro cavities in the insulation of H.V. power cables drastically affect the performance, the field distribution and hence the rating of these cables. It is well known that, P.D. deteriorates power cables and lead to its complete failure. This has adverse effects on the reliability and maintainability of power supply, which affects directly the production of industrial factories. In this work a study and investigation of the effect of partial discharges in cavities in the solid insulation of H.V. power cables is carried out. The field distribution and hence the rating of these cables were determined by modeling and simulation of these P.D. Cables with paper insulating material were tested and investigated at different voltages at low voltage, medium voltage and high voltage under alternating three phase voltages at room temperature. The cavity shapes, spherical and cylindrical, with different sizes were tried. The insulation thickness was varied. The location of the micro cavity in the insulation was changed between zero and 360. The position of maximum electric stress in cables was determined. The study was applied to three-core power cable. A developed simulation program using boundary element method was applied. The inception voltage was calculated and the applied voltage was changed as a function of the inception voltage. The discharge inception voltage was minimum at the conductor/insulation interface due to the high stress at this region. The result showed that cylindrical cavities are more severe than spherical ones. The simulation results are in good agreement with experimental findings and the practical experience. This shows the effectiveness and the value of this study as a non-destructive method of cables evaluation.