Effect of Voltmetric Unblock on Global Hosting Capacity

The increase in renewable generation has determined a strong increase in the amount of Distributed Generation (DG) connected to the distribution network. This introduced a set of challenges regarding network stability and unwanted island operations, which, if not appropriately addressed, may limit the network’s capability to host DGs. These two issues are addressed, in Italy, by adopting an Interface Protection System (IPS) for DGs in which the voltmetric unblock logic is implemented. The IPS aims to disconnect its generator by adopting different trip thresholds for any fault typologies. So, in case of a fault in the close “local” MV network, to avoid unwanted islands, the frequency range of the IPS trip thresholds is reduced; instead, in case of fault or perturbation on the HV network, to avoid DG disconnections, the frequency range of the IPS trip thresholds is increased. This paper explores the impact of this voltmetric unblock functionality on the grid hosting capacity, here called Global Hosting Capacity (GHC), by using a modified IEEE 9-bus network and adopting ETAP as a simulation tool. The GHC with and without voltmetric unblock is compared.