The most severe partial discharges and main insulation failures of 10 kV cross-linked polyethylene cables occur at the joint due to defects caused by various factors during the manufacturing and installation processes. The electric field distortion is analyzed as the indicator by the charge simulation method to identify four typical defects (air void, water film, metal debris, and metal needle). This charge simulation method is combined with random walk theory to describe the stochastic process of electrical tree growth around the defects with an analysis of the charge accumulation process. The results illustrate that the electrical trees around the metal debris and needle are more likely to approach the cable core and cause main insulation failure compared with other types of the defects because the vertical field vector to the cable core is significantly larger than the field vectors to other directions during the tree propagation process with conductive defects. The electric field was measured around the cable joint surface and compared with the simulation results to validate the calculation model and the measurement method. The air void and water film defects are difficult to detect when their sizes are less than 5 mm³ because the field distortions caused by the air void and water film are relatively small and might be concealed by interference. The proposed electric field analysis focuses on the electric field distortion in the cable joint, which is the original cause of the insulation material breakdown. This method identifies the defect and predicts the electrical tree growth in the cable joint simultaneously. It requires no directly attached or embedded sensors to impact the cable joint structure and maintains the power transmission during the detection process.

The use of mobile robots in substations improves maintenance efficiency and ensures the personal safety of staff working at substations, which is a trend in the development of technologies. Strong electric and solid magnetic fields around high-voltage equipment in substations may lead to the breakdown and failure of inspection devices. Therefore, safe operation range measurement and coordinated planning are key factors in ensuring the safe operation of substations. This paper first summarizes the current developments that are occurring in the field of fixed and mobile safe operating range sensing methods for substations, such as ultra-wideband technology, the two-way time flight method, and deep learning image processing algorithms. Secondly, this paper introduces path-planning algorithms based on safety range sensing and analyzes the adaptability of global search methods based on a priori information, local planning algorithms, and sensor information in substation scenarios. Finally, in view of the limitations of the existing range awareness and path-planning methods, we investigate the problems that occur in the dynamic changes in equipment safety zones and the frequent switching of operation scenarios in substations. Furthermore, we explore a new type of barrier and its automatic arrangement system to improve the performance of distance control and path planning in substation scenarios.

Grippers with a single rigid or flexible state have corresponding limitations, such as poor safety of rigid grippers and low precision of flexible grippers, which require complex algorithms and additional sensors to perform tedious tasks. Here, we design a reconfigurable gripper based on three fingers that can switch among the rigid, rigid bending, and flexible states. This adaptability enables the gripper to perform in diverse application scenarios. The flexible joints are locked and released by the back-and-forth movement of a slider mechanism, thus enabling switches between the rigid and flexible states of the fingers. When the fingers are in the rigid state, the structure resembles a conventional rigid gripper; when the fingers are in the flexible state, the spring-supported joints are driven by four cables. We have developed the mathematical models for the three states, tested the performance of different grasping configurations, analyzed the factors that influence horizontal grasping errors, and finally explored the application of rigid-flexible cooperative operations. Numerical and empirical experimental results clearly demonstrate the viability of the proposed gripper and its wide adaptability to different tasks.

This paper modeled the dry band formation and arcing processes on the composite insulator surface to investigate the mechanism of dry band arcing and optimize the insulator geometry. The model calculates the instantaneous electric and thermal fields before and after arc initialization by a generalized finite difference time domain (GFDTD) method. This method improves the field calculation accuracy at a high precision requirement area and reduces the computational complexity at a low precision requirement area. Heat transfer on the insulator surface is evaluated by a thermal energy balance equation to simulate a dry band formation process. Flashover experiments were conducted under contaminated conditions to verify the theoretical model. Both simulation and experiments results show that dry bands were initially formed close to high voltage (HV) and ground electrodes because the electric field and leakage current density around electrode are higher when compared to other locations along the insulator creepage distance. Three geometry factors (creepage factor, shed angle, and alternative shed ratio) were optimized when the insulator creepage distances remained the same. Fifty percent flashover voltage and average duration time from dry band generation moment to flashover were calculated to evaluate the insulator performance under contaminated conditions. This model analyzes the dry band arcing process on the insulator surface and provides detailed information for engineers in composite insulator design.

The reliable distributed monitoring system provides the real-time video observation from the power cable tunnels when the preinstalled communication system is disabled in an emergency. The spherical robotic prototypes are designed as the sensor node based on the analysis of the robot dynamic model. A novel self-constructed mobile wireless sensor network (MWSN) is proposed to realize the communication and positioning functions through the fusion of the Ad-Hoc and ultra-wideband (UWB) approaches. The Ad-Hoc network consists of multiple robot nodes as sensor carriers and relay stations to transmit large amounts of data from the accident scene to the monitoring terminal. The UWB network consists of UWB tags and bases on each node and implements the leader-follower (LF) strategy to create the robot formation. In order to maximize the monitoring area and maintain the reliability of the network, the traditional LF strategy is optimized based on the N-X algorithm subjected to the constraints of node number, Ad-Hoc communication and UWB positioning range, and the power tunnel boundaries. A self-constructed MWSN consisting of five robotic nodes ( N=5) is capable of covering 40 m of power cable tunnel, when the value of X is selected as 3. The network failure probability reduces from 73.5% ( X=0) to 0.2% ( X=3) when the malfunction probability of sensor node is 23.3% due to the accident condition in the tunnel. Finally, the simulation and experimental results show that the optimized LF algorithm increases 20.2% coverage of the network in the curve formation. The network transmits a monitoring video streaming with a 320×240 pixel resolution and a delay less than 150 ms. The real-time video observation from the accident scene is significant to formulate the emergency countermeasure and investigate the direct cause of the accident.

Long-term exposure to high temperatures can lead to the physicochemical properties of DC cross-linked polyethylene (XLPE) cable material degrading irreversibly, compromising its electrical performance. In this work, the effects of thermal aging on electrical tree initiation and the performance of treated cable material were examined. A Dam-flood model was constructed to investigate the effect of thermal aging on electrical tree initiation behaviors, where indices corresponding to aging performance and electrical tree initiation behaviors were obtained based on this model. Ultimately, by means of multiple linear regression estimation and a GM (1, N) model, prediction methods for the electrical tree initiation voltage ( U _50% ) and electrical tree initiation probability ( P ) were proposed. Results indicate that U _50% and P do not exhibit a monotonic change with an increase in thermal aging time and, based on the Dam-flood model, the recrystallization reaction can be regarded as the primary cause for this phenomenon. According to the Dam-flood model, the indices for gel content ( C_ge ), crystallinity ( X_c ), and dielectric DC breakdown strength ( E_b ) are significantly correlated with U _50% , and these three indices can be used to determine the changing regularity of U _50% . Furthermore, as the relative errors of the validation samples are all less than 15%, an equivalent relationship between P and the indices corresponding to thermal aging performance can be established. This could be used in future research to determine the electrical tree initiation of XLPE cable.