## 1 Introduction  
With rapid socio-economic development and industrialization, power cables have become a critical component of modern transmission systems [1, 2, 3, 4]. Power cable tunnels often feature complex architectures, such as shield tunnels, jacked pipes, and multi-tiered racks, resulting in intertwined cable layouts that form concealed spaces [5, 6]. Conventional inspection methods rely on fixed-route patrols and handheld sensors positioned close to the sensor carriers instead of the cables [7, 8]. Consequently, these approaches fail to detect defects in concealed areas, including insulation layer breaches, metal sheath corrosion, or carbonization of cable jackets caused by discharge on support structures. Such limitations significantly compromise the quality and safety management of high-voltage (HV) cable maintenance [9]. Therefore, we propose a methodology that enables sensors to operate close to cable surfaces to achieve comprehensive, blind-zone-free monitoring. The methodology aims at close-range, full-coverage inspection of high-voltage cable jackets under live-line operating conditions. Replacing manual labor with robotic systems can mitigate personnel risks, enhance operational safety, and improve efficiency, offering economic and practical advantages [10; 11]. Consequently, the live-line inspection robot with a multi-freedom degrees mechanic arm is selected as the carrier for the cable surface. Japan's Phase II robot [12], Shandong University's live-line repair robot [13], and Korea's insulator-cleaning robot [14] are the typical models among all the robots used for power system live maintenance [15; 16; 17; 18]. However, these robots employ metallic mechanical arms with base-mounted insulation layers. The extra insulation layer gives the mechanical arm excessive mass and volume [19]. Therefore, the arm's length is limited and cannot accurately inspect boundary features in concealed spaces (e.g., cable bends or pipe intersections) or detect visual blind spots (e.g., jacket wear on tunnel-facing surfaces) [20; 21]. In addition, the conventional metallic arm directly connected to the HV electrode leads to the following challenges. First, the corona discharge is likely to occur at any location with slight curvature according to the position and orientation of the arm [22]. Therefore, the corona mitigation measurement (e.g., corona ring) cannot be effectively installed at a fixed location of the arm [23; 24]. Second, due to its dimension limitation, the insulation layer cannot provide sufficient leakage distance for arc creepage [25; 26; 27]. Third, the motor and the controller malfunctions are likely to occur since the motor performance at the joint is affected by the electric field along the arm [28; 29; 30; 31]. To address all the challenges mentioned above, this study develops a bionic mechanical arm with self-insulating capabilities, mimicking the kinematic structure of human arms with the shoulder, elbow, and wrist joints. The joint is made of rigid insulating material (e.g., porcelain and epoxy) and driven by the insulating flexible material (e.g., polyester rope). Therefore, the mass of the proposed arm is significantly less than the conventional metallic arm. The material's low mass enables the arm to extend further, providing a longer creepage distance and greater working space than conventional metal arms. Compared with conventional live-working manipulators, the self-insulated cable-driven manipulator designed in this manuscript exhibits multiple differences, mainly in terms of insulation performance, application scenarios, structure, and mass. First, regarding self-insulation performance: Although conventional live-working manipulators have insulation designs, their motor actuators, manipulator skeletons, and other conductive components are still distributed on the manipulator body. Therefore, the manipulator lacks self-insulation performance.