The growing penetration of the Distributed Generation (DG) in the MV distribution power systems requires both to face technical operative problems and to re–examine the planning rules traditionally applied to radial passive networks. One of the important issues introduced in the new scenario is the setting of the protection systems in presence of DG which, during a fault, can contribute to the short circuit currents causing untimely operation of protection devices. The paper shows a planning protection study on a distribution radial network and proposes a procedure to verify the impact of GD on the protection systems and DG sensitivity during faults. The setting problem is formulated as an optimisation problem, modelled by genetic algorithm and a mathematical representation with operative and technical constraints is adopted. Specifically, the optimisation problem is constrained taking into account the thermal overloads of the electrical lines and transformers and the coordination times among all protective devices operating on the distribution network. Keywords: protection systems, distributed generation, electrical distribution networks, genetic algorithm PUBBLICATO A5055528 (PAD – 734796)