Measurements of electrical resistances and investigations of factors affecting corrosion and breakages of shielding layers in extruded three‐layer 6.6 kV XLPE cables

Corrosion and breakages of shielding layers are one of the factors for degradation of extruded three‐layer (E‐E type) 6.6 kV cross‐linked polyethylene (XLPE) cables. Tohoku Electric Power Network has been measuring electrical resistances of shielding layers in E‐E type 6.6 kV XLPE cables, and recently has found breakages of shielding layers. The authors performed an accelerated degradation test for shielding layers of E‐E type 6.6 kV XLPE cables by taking account of aqueous solution, temperature, heat cycles, bending stress, frequency of an applied voltage, and water‐proof layer in the test conditions, and investigated factors affecting corrosion and breakages of shielding layers. Corrosion, cracks, and breakages were found on shielding layers in the cables without water‐proof layer, but no crack was found in the cables with water‐proof layer, when heat cycles were applied to the cables, and shielding layers were supplied with artificial sea water. We investigated the suppressive effect of the cables with water‐proof layer on cracks and breakages of shielding layers by measuring tensile strengths of copper tapes obtained from the shielding layers of the cables with and without water‐proof layers.