Innovative solutions for protection schemes in autonomous MV micro-grids

In this paper the development of protection schemes for multi-phase and phase-to-ground faults in autonomous micro-grids is dealt with, accounting for the fact that a distribution “island” can be intentionally intended to operate for a long time duration (e.g. during maintenance in the main upstream network or due to economic advantages for the micro-grid electrical customers). The definition of an adequate protection scheme has to account for the extremely variable micro-grids architecture, characteristics and fault conditions that make difficult to protect them by using traditional criteria and schemes. The work aims at finding innovative protection schemes that involve minimum implementation costs for the distribution network operator. For this reason the proposed solutions make use of traditional or commercially available protective, switching and sensing devices, as well as telecontrol/automation techniques currently used in italian distribution networks. Traditional technologies employed by innovative protection schemes allow also to find interesting practical solutions to protect micro-grid feeders in presence of a high number of inverted-interfaced generators resorting to differential protection schemes. This is especially important when a micro-grid has to accommodate a large amount of generators based on renewable energy sources.