On multi-objective optimal reconfiguration of MV networks in presence of different grounding

The present work faces the traditional multi-objective optimal reconfiguration problem of a distribution grid including the safety issue in the objective functions. Actually, in many medium voltage networks still transformers with ungrounded neutral and with resonant grounded neutral coexist in the same area. This may be sometimes cause of problems during a single-line-to-ground fault if the ground electrodes of one or more cabins, initially designed for satisfying the safety conditions in a resonant grounded neutral network, after the reconfiguration are in a grounded neutral one or vice versa. In the paper a safety objective function is defined and the Non dominated Sorting Genetic Algorithm II used for solving the optimization problem formulated considering the minimization of the energy losses, the maximization of the load balancing among the transformers, and the minimization of the safety function. The safety function is defined both in the case of independent grounding systems and in the case of grounding systems interconnected by the metal shields of the cables. Also the effects of a Global Grounding System on the multi-objective reconfiguration problem so formulated are discussed. Finally a case study is analyzed presenting also a comparison between the Non dominated Sorting Genetic Algorithm II and a traditional Fuzzy Evolution Strategy algorithm.