EDF patented protection "PDTR" against resistive phase-to-ground faults in compensated MV distribution

Electricite De France is heading for a change in its MV-neutral policy by replacing the impedant grounding of its rural MV distribution network by arc suppression coils (Petersen coils). The main reasons for this modification are: 1) an important expansion of the underground network in rural environment. This leads to high phase to ground capacities of the outgoing feeders and causes thus increasing fault currents in impedant networks; 2) changes in international standards (insulation coordination...); 3) an increased sensitivity of the customers to their supply quality. The introduction of arc suppression coils allows both to reduce the fault current in single-phase-to-ground fault and to improve supply quality by reducing short supply disconnections. This modification of the neutral point treatment has to take into account the existing structure and outlines of French distribution networks. Adapting this solution to the existing networks made it necessary to develop new products including an automatic turning system, fast and compatible with cheap compensation coils. A different approach on the field of the protection of the feeders with zero-sequence wattmetric relays was also required. These new devices enable EDF to benefit the obvious advantages of compensated neutral point connection without modification of the MV network structures. In the following paragraph, network modelling and parameters consideration are given. Then the novel protection PDTR against high resistant faults is described as well as some experimental results obtained with this protection installed in one of EDF MV compensated network. (6 pages)