## 1 Introduction  
Cross-linked polyethylene (XLPE) insulated cables are widely used in medium-, high-, and ultra-high-voltage land-based and submarine direct current (DC) cables due to their excellent insulation strength, mechanical properties, and thermal performance [1, 2]. A typical cross-section of an XLPE cable is shown in Figure 1, where the white part is the XLPE insulation. However, the electrical properties of XLPE materials are influenced by factors such as the temperature and pressure parameters selected during the manufacturing process,  
Figure 1: Actual cable cross-section diagram. the manufacturing process itself, and aging effects. While the impacts of electrothermal aging [3] and crosslinking temperature [4] on XLPE have been studied in the literature, the influence of the manufacturing process itself on XLPE's properties remains underexplored. In the current study, the XLPE manufacturing process is classified into two main types: the three-layer co-extrusion method and the plane pressure molding method. These correspond to the industrial manufacturing process used for actual cables and the laboratory preparation of XLPE samples, respectively. Specifically, due to differences in cross-linking temperature uniformity and degassing efficiency caused by different manufacturing processes, physical properties (such as molecular weight, crystallinity, and amorphous region distribution characteristics) and impurity levels (by-product content) of XLPE samples are different. These differences ultimately affect the electrical properties of the material, such as electrical tree growth and partial discharge characteristics. For XLPE insulation in cables, its resistance to electrical tree formation and partial discharge is a critical concern, as the electrical tree is widely regarded as a primary cause of cable breakdown and insulation failure [5]. Electrical treeing is a process of insulation deterioration induced by high temperature and high electric fields, where dendritic discharge channels develop, often triggered by continuous partial discharge. Many studies have investigated the initiation, growth, and partial discharge characteristics of electrical trees in XLPE insulation within cables. [PERSON] et al. [6] examined HVDC cable samples and identified the voltage variation caused by electrical trees under constant DC and grounded DC voltages at different temperatures. [PERSON] et al. [7] used cable slices, extracting features from PRPD images to characterize electrical tree development, and employed convolutional neural networks (CNN) and pre-trained neural networks (NN) to classify insulation degradation levels. [PERSON] et al. [8] studied laboratory-made samples to explore the growth of electrical trees and partial discharge characteristics under DC voltage and proposed a discharge-avalanche theory to describe the growth dynamics of electrical trees. [PERSON] et al. [9] extracted characteristic quantities related to the growth parameters of electrical trees and partial discharge in laboratory-made samples, enabling insulation state evaluation based on gray correlation analysis. However, the comparison between the XLPE samples from different manufacturing processes on the resistance of XLPE insulated trees and partial discharge has not been reported. Therefore, this paper focuses on the XLPE samples (laboratory samples and actual XLPE cable slices) under two production processes, respectively, to test and compare their electrical resistance and physical and chemical properties. Then, the part of the manufacturing process that may be the source of the two differences is analyzed. First, the sample was prepared by using the common DC XLPE insulating material under laboratory conditions. At the same time, the XLPE sample was taken from the finished DC cable to prepare the pin-plate sample. After the sample was triggered by an AC electric field, a constant DC voltage was applied until the sample broke down, and the picture of the electrical tree and partial discharge signal in this process were recorded.