## 1 Introduction  
Offshore wind power offers multiple advantages, including abundant resources, consistent wind energy, and a smaller land footprint, contributing to its environmentally friendly profile [1; 2; 3]. A gas-insulated switchgear (GIS) on an offshore wind farm converter platform can significantly reduce the equipment footprint by up to 95% compared to an air-insulated switchgear, effectively reducing the cost of offshore converter platforms [4; 5; 6; 7; 8]. In harsh offshore environments, the enclosed design of the GIS prevents external factors such as humidity, salt spray, and pollution from eroding the equipment, further enhancing the stability of the system. Offshore wind farms often need to handle high-voltage and large-capacity power transmissions. DC GISs can effectively cope with these demands and provide a stable power transmission solution. Its high insulation performance and powerful current handling capability ensure efficient power transmission and meet the high-energy efficiency requirements of offshore wind farms [9; 10; 11; 12]. In a flexible DC transmission system, a DC GIS is the key switching equipment that ensures stable transmission of power from the wind turbine to the grid. Its high reliability and fast response capability can effectively deal with all kinds of power fluctuations and fault conditions and guarantee stable operation of the whole offshore wind power system. The reliability of the GIS is crucial to safety of the platforms, and surge arresters are essential equipment for protecting the GIS from overvoltage. Surge arresters in DC systems are subjected to continuous DC voltage. Overvoltage in DC systems can be long-lasting, so surge arresters must have a greater energy absorption capacity and need to be able to effectively absorb and dissipate the large amounts of energy generated in the event of a DC fault or lightning strike, avoiding arrester failure due to heat accumulation. Due to the high voltage of DC systems, a single arrester is often unable to withstand the full voltage and current load alone. Multiple columns in parallel design can increase the energy absorption and dispersion capacity but need to pay special attention to the uniformity of the current distribution to avoid overloading some columns due to uneven current distribution between parallel columns. In high-voltage systems, surge arresters are connected in parallel to improve the energy absorption capacity and reliability. Nonetheless, the difference in reference voltage of each column variator leads to uneven current distribution, resulting in uneven energy absorption across the parallel columns. The conductivity of ZnO varistors in surge arresters in a specific voltage and current range shows a negative correlation with temperature [13; 14]. Hence, high-temperature arrester column resistivity decreases, resulting in more current flow into this arrester column. The formation of positive feedback increases the high-temperature arrester column temperature, which leads to part of the variator aging faster, and it even causes an explosion in the arrester column [15]. It affects the overall performance and lifetime of the arrester. Therefore, studying the uniform current characteristics of multi-column parallel arresters in a DC GIS is significant for optimizing arrester design and improving offshore power system reliability. Most of the studies on the current distribution characteristics of multi-column parallel arresters are based on the reference voltage of the ZnO varistor, and most of the research has been conducted on the application of alternating current and cannot be directly applied to DC. The relative deviation in the reference voltage of the ZnO varistor of each column of the arrester is small. The current distribution between the columns tends to be uniform. [PERSON] [16] optimized the excellent electrical properties of ZnO varistors by adjusting the sintering process. The optimized varistor has a higher voltage gradient, which reduces arrester length and residual voltage.