Investigation of the impacts of energy storage systems on energy transmission lines

Today's energy transmission systems face critical issues such as frequency fluctuations, voltage instability, and inertia deficiency due to the increasing integration of renewable energy sources (RES) and the decreasing share of synchronous generators. This thesis study comprehensively examines the technical effects of energy storage systems (EDS) on grid performance in transmission lines. In the study, a 9-bus test network was modelled using the DIgSILENT PowerFactory 2023 programme, integrating synchronous generators, a 100 MW photovoltaic (PV) plant, and a 30 MW EDS. The scenarios included critical conditions such as a 250 ms three-phase short circuit and a 70% sudden load increase, and were analyzed using the RMS simulation method. The findings showed that PV integration caused the frequency to rise to 52 Hz after a three-phase short circuit, leading to rotor angle instability. The EDS integration, on the other hand, brought the frequency back to the nominal value (50 Hz) with a virtual inertia mechanism and a response time of lEDS than 50 ms, damped the rotor oscillations, and ensured system stability. In a variable load scenario (70% load increase), the frequency dropped to 48.5 Hz and became unstable in the system without EDS, while the system remained stable at 49.8 Hz with EDS support. These results demonstrate the capacity of EDS to provide frequency regulation, transient stability, and virtual inertia in renewable energy-intensive grids. This thesis study fills the technical gap in high-power demands on transmission lines, unlike distributionlevel-focused EDS research in the literature. Future studies are recommended to explore the integration of different storage technologies into transmission infrastructure and conduct cost-benefit analyses.