Development of aerial fibre optic cables for operation on 400 kV power lines

The authors report on advances in the development and testing of self-supporting aerial fibre optic cable to be used on high-voltage grid networks. The environmental effects they must withstand are first discussed with emphasis on the influence of the electric field created by neighbouring conductors. Finite element analysis is used to determine the voltage on the cable under different conditions of vertical and horizontal position, conductor phasing and distance from the tower. Dry banding and the consequent arcing have been modelled, together with the influence of electrode shape on voltage stress at the fixing point. Reduction of the mechanical and electrical stress concentrations at the earth grip by the use of a stress-relieving trumpet is shown to give a dramatic improvement of the erosion resistance of the cable. Test procedures are described which are recommended as the basis for a qualification specification. The concept of suppressing discharges on the sheath surface by use of a partially conducting layer is investigated. Field experience on 132 and 400 kV lines in the UK is described.