Analysis and Simulation of Electromagnetic Transient Process of Transformer Under the Action of Geomagnetic Induced Current

Geomagnetic induced current (GIC) is a low-frequency current induced in power systems by abnormal geomagnetic activities, which can cause transformer core saturation, excitation current distortion, excessive heating, reactive power loss increase, and even threaten the safety of the entire power grid. This paper focuses on the transient response of transformers under GIC. First, it analyzes the principle of transformer transient processes under GIC, including the action path of GIC in power grids and the calculation of core saturation processes, especially the role of multi-winding structures in delaying saturation. Then, an EMTP model based on a real 220 kV substation is built to simulate the actual transformer response under GIC injection. The model involves different transformer winding connections (such as YYNy and YNYNd) and observes the current distribution, neutral point voltage, and reactive power loss during the transient process. Simulation results show that transformers with grounded star windings and delta windings (YNYNd connection) generate induced currents in other windings to counteract the DC magnetic field from the injected GIC, resulting in a longer transient process and a slower saturation of the core compared to other connections (e.g., YYNy). The reactive power loss characteristics effectively reflect the transient process, verifying that the winding structure significantly affects the transformer’s response to GIC. This study provides insights into understanding and mitigating the impacts of GIC on power transformers and systems.