## 4 Analysis and Discussion
### Analysis of the Influence of Material Parameters on the Resistance of XLPE to DC Tree  
Based on the analysis of Figures 8-10, it can be concluded that DC-XLPE exhibits superior resistance to DC electrical treeing and partial discharge compared to Cable-XLPE. From the perspective of material properties, both crystalline and non-crystalline regions coexist within XLPE insulation. These regions show significant differences in resistivity and dielectric constant, with the non-crystalline regions of XLPE serving as the preferential pathways for electrical tree propagation [20]. According to the literature [21], low crystallinity, large spherulites, and high impurity levels are the ideal conditions for the initiation and growth of electrical trees. A crystalline structure characterized by high spherulite density but smaller volume can reduce the concentration of impurities and microvoids, while also preventing the formation of defect interfaces between the crystalline and amorphous regions. Therefore, the crystalline structure is a critical factor in preventing treeing in cable insulation.  
XRD results show that, between the two types of XLPE, DC-XLPE has slightly lower crystallinity but marginally larger crystallite size, although the differences are minimal. Hence, the crystalline morphology revealed by XRD is not the reason for the observed differences in DC electrical treeing resistance and partial discharge performance between the two types of XLPE in this study.  
Molecular weight also affects crystallization properties, as a narrower molecular weight distribution weakens interactions between large and small molecules, leading to the formation of denser crystalline centers and enhanced resistance to electrical treeing. In addition, there are studies on molecular weight and XLPE material structure [22; 23; 24]. They reveal that an increase in molecular weight generally results in reduced free volume, increased viscosity, and stronger intermolecular forces, which in turn reduce conduction currents. Removing low molecular weight chains helps to reduce heterocharge accumulation, conduction currents, and carrier mobility under DC fields. Moreover, an increase in molecular weight leads to increased viscosity and slower crystallization rates, which contribute to higher dielectric strength.  
According to the GPC results, the molecular weight of DC-XLPE is significantly higher than that of Cable-XLPE, with a more concentrated molecular weight distribution. This  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & **Peak** & **Area Ratio** & \multirow{2}{*}{\(M_{\mathbf{n}}\)} & \multirow{2}{*}{\(M_{\mathbf{w}}\)} & \multirow{2}{*}{\(M_{\mathbf{z}}\)} & \multirow{2}{*}{\(M_{\mathbf{w}}\)/\(M_{\mathbf{n}}\)} \\  & **Number** & **(\%)** & & & & \\ \hline \multirow{2}{*}{DC-XLPE} & P\({}_{1}\) & 96.765 & 14,389 & 78,488 & 248,403 & 5.455 \\ \cline{2-6}  & P\({}_{2}\) & 3.235 & 83 & 183 & 296 & 2.220 \\ \hline \multirow{2}{*}{Cable-XLPE} & P\({}_{1}\) & 100.00 & 3865 & 21,671 & 49,042 & 5.607 \\ \hline \hline \end{tabular}
\end{table}
Table 2: GPC parameters of different XLPE insulation.  
Figure 12: GPC curves of different XLPE samples.  
leads to lower conduction currents and higher dielectric strength, which may explain why DC-XLEP demonstrates better resistance to electrical treeing and partial discharge.