Synchronous condensers with flywheel for power systems with high penetration of RES: the case of Italian transmission grid

Today power systems are facing challenges due to the fast changes in the generation mix: Renewable Energy Sources (RES), especially Photovoltaic (PV) plants and wind generators in Dispersed Generation (DG), are largely replacing conventional generators. This change in the generation mix affects the operation of the power systems. The reduction of the synchronous generators in service, particularly during the low demand phases, makes the system inertia decrease and consequently the Rate of Change of Frequency (ROCOF) increases. In addition, there is a reduction in the short-circuit level and the transmission grids are facing overvoltage problems in low load conditions. In this scenario, Synchronous Condensers (SCs) with flywheel can give a support for the secure and reliable operation of the power systems with high penetration of RES. The present paper deals with the specific case of the Italian Transmission Grid handled by TERNA, the Italian Transmission Operator (TSO), which is in fact a concrete example of a power system with high penetration of RES. TERNA is planned and managed a plan of installation of SCs with Flywheel for facing the issues above reported. The paper outlines the areas that are most affected by this plan, explaining the reasons and the potential benefits; besides a criterion for the optimal installation of SCs with Flywheel in the Italian transmission grid is proposed.