Evolution of the French MV cable system

The 20 kV synthetic cable on the French distribution network has an excellent experience feedback; the very innovative design at the introduction of this cable on the network, has barely changed during 20 years of operation. Meanwhile, significant improvements of the synthetic insulation, on the material point of view as well as on the industrial process, have led to an extension of this technology to the highest voltage levels and to the development of more efficient accessories. Due to these technical achievements, EDF and the manufacturers of this product have considered that its optimisation was possible. The chosen way to directly draw benefit from progress of the synthetic insulation was to reduce the insulation thickness of the cables from 5.5 mm to 4.5 mm. These optimised cables were developed, and the corresponding connection accessories were also adapted. Taking into account the reductions of the cable diameters, and the increase in the electric field, the compatibility of these new cables with the accessories has been carefully studied. Accessories were validated according to the European document HD 629.1 the French document C 33-001, and additional breakdown tests. Field experimentation has been done and showed that some tools needed to be adapted. This project required good practice of the jointers in cable preparation. Since March 2000, Electricite de France, provisions exclusively this new cable and this has allowed a sensible reduction of the cost of 20 kV underground cables