Simulation of High-Frequency Current Transmission Characteristics of Turn-to-turn Faults in ±800kV Converter Transformers

In the online monitoring of the operating status of converter transformers, the proper setting of alarm thresholds is crucial for ensuring their safe and stable operation. In the past, difficulties in threshold analysis arose due to issues such as deviations from manual experience, poor equivalence between small cavity models and actual transformer discharges, high costs of full-scale transformer discharge tests, and limited fault location detection. To address these problems, this paper establishes a multi-capacitor network model for the ± 800kV converter transformer. By simulating turn-to-turn faults at different winding positions, the ratio of high-frequency current magnitude between different grounding positions ($3 \sim 30 \mathrm{MHz}$) and that at the fault location (referred to as the transfer ratio) was obtained. For instance, when a fault occurs at the valve-side winding, the transfer ratio of neutral point grounding ranges from $2.2 \%$ to $56.8 \%$; when a fault occurs at the grid-side winding, the transfer ratio of neutral point grounding ranges from $\mathbf{2. 5 \%}$ to $68.8 \%$. The simulation results reveal the transfer characteristics of high-frequency currents: the closer the grounding position is to the fault source, the higher the transfer ratio of the highfrequency current at that grounding position. The findings provide a theoretical basis for threshold analysis in the active defense technology of converter transformers.