Optical techniques to evaluate shield/insulation interfaces in XLPE cables

Contaminants and protrusions at the shield/insulation interfaces of polymer-insulated high-voltage cables can be the initiation sites of water and electrical treeing which lead to insulation failure. The smoothness of the interfaces is, therefore, is of critical importance to the long-term performance of cables. An optical technique to evaluate the surfaces of extruded semiconducting tapes and also shield/insulation interfaces of cables is described. The results presented demonstrate the feasibility of the technique on both tapes and cables. A comparison of the measurements of protrusions on extruded tapes using the technique and SEED is included