Improving safety of cable networks by modeling deflectors of cable accessories

In the last five years several failures occurred in new “smart grid” networks at Distributed Generation Units (wind farms, heat couplers, etc.). These failures occur in medium voltage (MV) cross-linked polyethelene (XLPE) cable circuits after a few years in operation. The structure and critical parts in MV underground cable accessories were defined through literature. A screening is the weakest point in a termination. Terminations without grading suffered from the high electric field peak and would eventually have failed with high voltage. The most critical point of a cable joint is the cone edge of the connector. It is necessary to homogenize the electric fields. The material properties of the stress control mass and deflectors play a key role in the durability of a cable accessories. The optimization needs an accurate numerical models which are able to take into account the multilayer stress grading materials. This paper deals with a our new hybrid numerical method, so called Hybrid Boundary Elements Method, which permits to compute the electric field distribution in insulating configurations, using optimal design of deflector's cones and stress grading materials. Two methods have been mixed to model the accessories: a boundary integral method and a equivalent electrodes method. The idea was to take advantages of each of these methods. Some modeled cable accessories are presented. Analyzed design is compared to an existing cable accessories design.