In this paper, we analysed the growing penetration of generating units from renewable energy sources in transmission power systems. Among the possible effects of the interaction of distributed generation (DG) with transmission systems, we considered the abnormal operating conditions caused by short circuits in the transmission systems and the resulting voltage sags that occur in the network. A systematic method is presented for analysing the voltage sag behaviour of any transmission system in which large DG units are connected to the transmission system by means of High Voltage/Medium Voltage (HV/MV) stations. The method proposed for obtaining the voltage sags is the fault position method (FPM), from which we derived a graphical visualization of the during-fault voltage (DFV) matrix as a valuable tool to obtain an immediate measure of the propagation of voltage sags in the network. The results obtained were based on a portion of a real transmission system. The system that we considered is an actual portion of the Italian transmission system, and all of the quantities we used were obtained from the data of the Transmission system operator (TSO).

This paper investigates the impact of renewable energy source (RES) integration on the Sicilian transmission network, considering the commissioning of new Mediterranean interconnections, namely the TUN-ITA and the Tyrrhenian Link. The expansion of transmission infrastructures and the increasing penetration of RES require an assessment of the Sicilian power system’s capability to accommodate high levels of power injection. This study was carried out in collaboration with the Italian transmission system operator Terna S.p.A. and the University of Palermo. It aims to evaluate the evolution of transmission line loading under future RES integration scenarios consistent with grid connection requests submitted to Terna and with national energy policy targets. The proposed methodology integrates micro-zonal assessments of wind and solar potential, estimation of capacity factors, development of RES capacity expansion scenarios, and steady-state power flow simulations. The simulations were performed using WinCreso^® software version 7.69 for three time horizons: 2028, 2029, and 2035. The results show the most congested transmission lines and the network areas most exposed to congestion. The analysis provides operational insights for prioritizing grid reinforcement measures and proposes a replicable methodological framework for other transmission system operators facing similar RES integration challenges.

A replicable methodology for testing the size and placement of Battery Energy Storage Systems connected to high-voltage transmission networks is presented in this study. The proposed approach involves the power flow analysis inside a Renewable Energy Zone, namely a high-renewable area prone to grid congestion during peak generation periods, based on time-series hourly analysis over a critical month. The model includes detailed operational descriptions such as lines ampacity, battery state of charge limits, round-trip efficiency, self-discharge behavior, and ramp rate restrictions. The methodology distinguishes itself by its simplicity, flexibility, and use of open-source tools, making it a valuable asset for supporting future transmission planning in high-renewable-energy scenarios. The model was developed in Python (version 3.12) using the open-source Pandapower library, introducing an innovative constraint management criterion, and validated against real data provided by the national Transmission System Operator. The approach was then applied to a portion of the Sicilian grid with massive wind and solar penetration. Results show that strategic allocation of batteries leads to a significant reduction in line overloads (up to 13 GWh mitigated in one month), improves the dispatch of renewable energy generated within the Renewable Energy Zone and allows a more sustainable exercise of the power system.