UHV DC wall bushing is the only channel connecting the valve hall and the DC electric field in the converter station. For the epoxy - SF6 gas composite insulation wall bushing, the main insulation material is the epoxy/crepe paper core and SF6 gas. The transient process of establishing the DC electric field for the wall bushing is impacted by the temperature gradient. In this paper the 3-D temperature field of the wall bushing has been simulated considering the effect of heat conduction, convection and radiation. The simulation results have been confirmed using a temperature rise experiment. The transient process of the wall bushing under the actual operation condition has been simulated using the gas saturation current density method. The temperature impact on space charge density in the core, the surface charge on the interface, and the electric field distribution on the bushing is investigated. In this way a theoretical basis is developed for the optimal design of the bushing that is conductive to the safe operation of the bushing.

Long-term operation of high voltage direct current at elevated temperatures can result in the accumulation of surface charges in DC gas-insulated transmission line (GIL) insulators. Such a phenomenon leads to localized electric field distortion, increasing the risk of surface discharge. The analysis of interaction behaviors between surface charge and space charge at interfacial domains of GIL insulators is a complex task, which requires a comprehensive understanding of physical mechanisms of the gas–solid interface charging. In this work, a two-dimensional bipolar charge transport and interaction (2D BCTI) model is established, with the consideration of both surface and space charge dynamics. Pulsed electroacoustic tests and surface potential measurements are conducted on DC GIL insulator materials under different electrical-thermal coupling conditions. Experimental results exhibit great consistency with the predictions from the 2D BCTI model. The local accumulation of space charge near interfaces has certain effects on surface potential distribution, which in turn influences charge injection behavior from electrodes. In comparison to traditional surface charge simulation models, the consideration of space charge–surface charge interaction behaviors proves to be essential for estimating the polarity and amplitude of surface potential distribution. This model holds promise for assessing charge characteristics in electrical equipment where direct measurement is challenging.

Converter transformer valve side bushing is an irreplaceable key equipment in the UHVDC transmission project. In the process of operation, the surface of the epoxy resin impregnated paper (ERIP) core will produce partial discharge due to insulation defects, and the formed discharge arc will destroy the insulation layer, which seriously threatens the safe and stable operation of the valve side bushing. In this paper, an arc ablation experimental platform was built to study the thermal response characteristics of ERIP in SF ₆ arc ablation. The surface microscopic morphology and dielectric properties of the samples before and after ablation were compared and analyzed, and the intrinsic mechanism of surface insulation failure was further revealed by a mathematical model. The results show that the huge heat generated by the arc discharge causes the decomposition of the epoxy resin, leading to the gradual increase of the internal porosity and permeability of the material, and the carbon layer structure will be formed on the surface after complete pyrolysis. With the increase of the arc action time, the ERIP is gradually transformed into carbide and pore products, the material surface resistance decreases, the roughness increases, and a local failure region is formed, which reduces the surface electrical properties of the material and ultimately leads to the failure of surface insulation.

In response to the problems of time-consuming simulation of temperature field of resin impregnated paper (RIP) bushings on valve side of converter transformer, which result from a high degree of freedom and complex coupling mechanism, a deep learning surrogate model (DLSM) suitable for fast prediction of bushing temperature is proposed. The model consists of two parts: proper orthogonal decomposition (POD) reduced order model based on back propagation neural network (BPNN) and convolutional neural network (CNN), which predict the outside and inside part of bushing respectively to improve the accuracy. Subsequently, the temperature fields calculated by the finite element method (FEM) and DLSM are compared, and the average relative error is less than 0.7%. In addition, the influence of different train sizes and input perturbations on the precision of the model is analyzed, which is good when at least 108 samples are trained. The prediction results of the model with input perturbation within 5% are similar to the FEM results. Finally, the time for the model to predict 30 test conditions is 1.5s, which is much less than the time of finite element simulation. The research results show that DLSM has high precision, robustness and prediction speed. The method in this paper provides a feasible solution for online monitoring and digital twins of bushings.

As the key component of the conductor of the gas-insulated power transmission equipment, the electrical connection structure bears high current, high stress and high temperature for a long time. Electrical contact failures become an important issue, while it’s failure characteristics and mechanisms are ambiguous so far. In this paper, based on complex electrical connection structures of gas-insulated transmission line (GIL), equivalent tests were conducted on the contact failure characteristics of such structure. Result shows that poor contact of the such electrical connection structure will cause two types of situations: micro-gap discharge and contact overheating. The causes of both are different. Firstly, micro slip is a kind of cause of discharge faults despite the separation gap is small. The current transfer area (b) of such contact structure is the main position where the arc starts. The contact stability at that location should be fully considered in the layout of such electrical connection structure. Secondly, combined with the surface morphology and element distribution, the mechanism of contact discharge and the source of metal particles are further explained by the occurrence of coating peeling and material transfer behavior. Finally, the difference in contact state is the main reason for a few contacts overheating. There is a significant temperature difference between contacts in different contact state. The temperature rises nonlinearly with the increase of the current under the condition of uneven current carrying. The above research can provide a practical basis for fault analysis and prevention of such electric contact structures in the UHV gas-insulated power transmission equipment.