## 8 Conclusions  
In this paper, the characteristics of charge accumulation and electric field distribution on the surface of a \(\pm\)200 kV DC GIL basin-type insulator was investigated under multi-physical field coupling conditions. The main conclusions of this study are as follows:  
1. The insulator bulk conductivity and surface conductivity parameters under different temperature and electric field conditions were determined experimentally, from which the corresponding fitting equations were established. The insulator bulk conductivity increases exponentially with increasing temperature and electric field, whereas the surface conductivity increases exponentially with increasing tangential electric field.
2. When the DC GIL operates at a current of 3150 A, the temperature of the central conductor reaches a maximum of approximately 63.8 \({}^{\circ}\)C, while the enclosure's temperature remains at a minimum of about 30.4 \({}^{\circ}\)C. The maximum temperature of the insulator near the conductor is approximately 62.8 \({}^{\circ}\)C, in contrast to the minimum insulator temperature recorded near the enclosure, which is around 32 \({}^{\circ}\)C. Notably, convex surface temperatures consistently exceed those of concave surfaces, with significant thermal variations observed across different radial orientations (12 o'clock, 3 o'clock, and 6 o'clock).
3. Under DC voltage, the electric field distribution gradually transitions from a capacitive field to a resistive field. On the insulator's convex surface, positive charges progressively accumulate, while negative charges increase on the concave surface. The surface charge accumulation is more rapid in the high-temperature regions of the insulator. The surface charge and electric field exhibit significant changes within the first 40 h. After 300 h, surface charge accumulation approaches equilibrium, and the electric field stabilizes. Following stabilization, the difference in surface charge across different radial directions is substantial, whereas the difference in the electric field remains relatively small.
4. When voltage polarity reversal occurs, the charges accumulated on the insulator surface cannot be fully dissipated within a short time frame. This residual charge after the reversal significantly distorts the electric field along the surface, resulting in an increase of 13.6% in maximum field strength on the convex surface and 47.2% on the concave surface. Notably, the concave surface exhibits the most severe distortion of the electric field following polarity reversal.  
Conceptualization, [PERSON] and [PERSON]; methodology, [PERSON] and [PERSON]; software, [PERSON]; validation, [PERSON] and [PERSON]; formal analysis, [PERSON] and [PERSON]; investigation, [PERSON] and [PERSON]; resources, [PERSON]; data curation, [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON]; visualization,  
Figure 19: Comparison of simulation results with experimental data in the literature.  
[PERSON] and [PERSON]; supervision, [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON] All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Basic Research Special Project of Natural Science Foundation of Shenyang, China (24-202-6-02).  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
This paper has received support from the Institute of High Voltage and Power Systems at Shenyang University of Technology. The author extends gratitude to [PERSON]. In addition, the author sincerely thanks [PERSON].  
The authors declare no conflicts of interest.