Innovative solutions to control unintentional islanding on LV network with high penetration of distributed generation

During the last 3 years the Italian Distribution Network has experimented a dramatic increase of Distributed generation (DG) connected both at MV and LV levels, driven by incentive policies mainly to photovoltaic (PV) generators. The total amount of DG has reached the record level of 21 GW, out of which 4,2 GW connected to the LV network. Considering the high penetration of distributed generation the Transmission System Operator (TSO) asked additional technical requirements in the Grid Code to involve DG in the primary regulation during the frequency transient of the transmission grid. These new requirements have been reflected in a new issue of Italian LV connection standard (Italian Norm CEI 0-21) which foresees that all LV generators (synchronous, asynchronous or static) must be provided with a determined active Power - frequency regulation curve and must sustain the main network in the frequency range 47.5 - 51.5 Hz. These conditions may cause, under specific network conditions (e.g. MV ground fault) an uncontrolled network island. This paper focuses on the new connection criteria and on the possible solutions that Enel Distribuzione is experimenting to address the unintentional islanding on LV networks.