In order to ensure the safe and stable operation of capacitor voltage transformer (CVT), improve its insulation reliability, the insulation state of CVT was evaluated based on improved criteria importance through intercriteria correlation (CRITIC) method. Firstly, the CVT was conducted the artificially accelerated thermal ageing, and its capacitance and dielectric loss factor, polarization and depolarization current, voltage and current were tested under different ageing cycles. The results show that after ageing, the total capacitance of CVT increases from 10.106 nF to 10.155 nF, the time constant of the third branch increases from 62.35 s to 82.80 s, the current and voltage phase difference increases from 96.3° to 97.8°, and only the primary side apparent impedance value decreases among the insulation characteristic parameters. Subsequently, the CRITIC method was improved by residual expectation coefficient and activation entropy, and the improved CRITIC method was used to weight and score the CVT insulation characteristic parameters. In the empowerment results, the weight of 0.1 Hz low frequency dielectric loss factor is the largest, which is 0.323 3, and the weight of C1 dielectric loss factor is the smallest, which is 0.091 2, and the improved CRITIC method solves the problem of information incompleteness. Finally, the insulation score of CVT was correlated with the operating time under actual working condition, and its insulation status was evaluated. When the insulation score is 0 points, the corresponding operating time under working condition is 29.88 years, which is consistent with the actual project. According to CVT insulation score, the internal insulation state can be judged.

Interfacial discharge between XLPE and SIR in cable joints is one of the main causes of cable failure. In order to improve this phenomenon, the XLPE sample surface was treated by plasma silicon deposition with different time, and the micro-morphology and interface discharge tests were carried out. The results show that the plasma silicon deposition technology can effectively improve the voltage resistance of XLPE/SIR interface. With the increase of plasma silicon deposition treatment time, the surface roughness of XLPE sample decreases at first and then increases, and its change trend is the same as that of the initial discharge voltage, breakdown voltage, and voltage increase amplitude of XLPE/SIR interface, and is opposite to that of the surface resistivity. The XLPE sample after 3 min of plasma silicon deposition has the smallest surface roughness (R _a=41.8nm) and the largest surface resistivity (857×10¹² Ω). Under this treatment time, the XLPE/SIR interface has the largest actual contact area, the fewest micro-pores, and the largest increase in breakdown voltage. Among them, the breakdown voltage increases by 66.7% compared with the untreated XLPE/SIR interface.

Converter transformer is the key equipment in high-voltage direct current (HVDC) transmission system, and its valve-side windings are subjected to complex composite voltage waveforms during operation. The existing researches primarily focus on partial discharge characteristics under single voltage form or AC-DC composite voltages. However, due to the influence of power electronic devices such as converter valves, converter transformers also endure pulsating voltages. In this paper, the impact of positive polarity DC pulsating voltage on partial discharge of oil-paper insulation under actual operating conditions was studied, and the partial discharge characteristics of two typical oil-paper insulation defects, needle tips discharge in oil and surface discharges on oil-paper boards, were obtained under DC pulsating voltage. The results show that the DC component only changes the frequency and amplitude of partial discharge, and has same effect on the two types of defects. As the amplitude of the pulsating component increases, the discharge pulses of the two types of defects increase gradually, forming pulse clusters and exhibiting significant polarity effects. The pulse clusters for needle tips discharge in oil are concentrated on the rising edge, while those for surface discharges on oil-paper boards are concentrated on the falling edge.

Surface flashover at the gas-solid interface of basin type insulator is the key problem that causes the ultra high voltage GIS/GIL failure, and it is the technical bottlenecks restricting the development of advanced electrical transmission system. In order to improve the DC flashover performance of the basin type insulator in SF₆/N₂ gas mixture, the zinc oxide (ZnO) nanoparticles with different contents were added to the epoxy resin to obtain epoxy/zinc oxide (EP/ZnO) coatings, and the EP/ZnO coatings were coated on the surface of epoxy material. Then the transport parameters and flashover performance were tested. The results show that EP/ZnO coating increase the shallow trap density and reduce the shallow trap energy level of epoxy composite, and increase the carrier mobility. The electrical conductivity of the epoxy materials coated by EP/ZnO coatings with 15% and 20% ZnO mass fraction show nonlinear characteristics, the existence of the coatings can reduce the electric field distortion and promote the dissipation of surface charge. The EP/ZnO coating can remarkably uniform electric field distribution and effectively inhibit the charge accumulation on the surface of epoxy materials, and improve the DC flashover performance. When the mass fraction of ZnO is 20%, the DC flashover voltage of the epoxy composite increases by 15.42%.

The ablation of the buffer layer of high-voltage cables is accompanied by the release of characteristic gas, so the characteristic gas can be used as an indicator for the detection and evaluation of ablation faults. However, the correlation between the type and concentration of released gas and the degree of ablation is still unclear. In this paper, a buffer layer ablation simulation experiment platform was established. After comprehensive consideration, C₂H₆, C₂H₄, C₂H₂, and CO were selected as the characteristic gases for buffer layer ablation evaluation, and the change law of their stoichiometric characteristics with buffer layer ablation degree and moisture content were analyzed. The results show that the average molar mass of characteristic gas decreases with the increase of moisture content in buffer layer, and the ratio of C to H atoms in characteristic gases under humid conditions is higher than that under dry conditions. The concentrations of C and H atoms continuously increase with the burning time, and with the increase of burning time, the concentrations of C and H atoms first decrease, then increase and then decreases, and finally monotonically increase with the increase of moisture degree. Analysis suggests that the differences of damage to the buffer layer structure under different conditions are the reasons for the change in the stoichiometric characteristics of the released gas.

As a key device in ultra-high voltage and extra-high-voltage transmission projects, the deflagrate accidents of bushings seriously threaten the safe and stable operation of the power system. Adhesive impregnated paper bushing is an alternative to oil-impregnated paper bushings with deflagration risks, while there is relatively little research on the thermodynamic behavior of its core insulating material of epoxy resin impregnated paper during arc faults and the risk of bushing deflagration. In this paper, the thermogravimetric experiments and differential scanning calorimetry analysis at different heating rates were conducted on epoxy resin impregnated paper, and its thermal decomposition process was analyzed. Flynn-Wall-Ozawa (FWO) method and Coast-Redfern (CR) method were used to obtain the pyrolysis kinetic models of epoxy resin impregnated paper at high temperature in an oxygen-free environment. The results show that the thermal decomposition process of epoxy resin impregnated paper in adhesive impregnated paper bushing can be divided into three stages: epoxy melting, endothermic reactions, and decomposition gasification, and the first two stages conform to three-dimensional diffusion model, random nucleation and subsequent growth model, respectively. After an arc breakdown fault occurs in bushing cores, the thermal decomposition mass loss of epoxy resin impregnated paper is as high as 90% under the effect of high temperature. The high temperatures and gas expansion produce high amplitude internal stress inside the core, which leads to core cracking and even explosion.

High sensitivity defect detection technology is urgently needed to evaluate the health status of gas insulated metal enclosed switchgear (GIS) insulator. In this paper, a defect detection method for GIS basin insulator based on ultrasonic scanning frequency signal injection was proposed. The propagation law of scanning frequency ultrasonic signals on clean/defective basin insulators were investigated by simulation and experiment, and three defects including internal bubbles, surface cracks, and surface metal particle attachment were considered. In the simulation and experiment, the ultrasonic emission and reception probes were located opposite the flange of the basin insulator. The ultrasonic scanning signal was a frequency conversion sine wave with an amplitude of 1 V and a frequency range of 0.5-1 MHz, which was energized by the transmitting probe and injected into the basin insulator through a flange, and the ultrasonic signal was received by the receiving probe on the opposite side. The results show that the ultrasonic signal directly propagates through the basin insulator to the receiving piezoelectric probe, and the amplitude of the time-domain ultrasonic signal received on the defective insulator is higher than that on the clean insulator, but it is still difficult to be used as a basis for evaluating the health status of the insulator. The main frequency of ultrasonic signals propagated through detective insulators is lower than that propagated through clean insulators. The main frequency signals propagated through clean, crack containing, metal particle defective, and bubble defective insulators are 24.00, 14.83, 10.51, and 12.13 kHz, respectively, which can be used as the basis for defect detection of GIS basin insulators.

The cable joint is the weakest link in the cable line, and the contact resistance between the conductor and the connecting pipe at the aluminum alloy conductor cable joint is the key factor affecting the temperature distribution and failure rate of the cable joint. In order to study the influence of different crimping processes on the temperature distribution characteristics of cable joints, a 35 kV aluminum alloy conductor was used as the research object, and the contact resistance between conductor samples with different crimping percentages and connecting tubes were measured through the contact resistance measurement circuit. The quantitative relationshipes between contact resistance and crimping percentage under two crimping processes of pit pressure and confining pressure were obtained. The electro-thermal coupling model of a cable joint with conductor cross-sectional area of 400 mm² was established by COMSOL finite element simulation software, and the corresponding relationship between contact resistance and temperature distribution characteristics of cable joint under different crimping processes was studied. The results show that the contact resistance increases with the increase of the crimping percentage. Under the premise of ensuring that the maximum temperature of the long-term operation of the cable does not exceed 90℃ and meeting the mechanical performance requirements, the crimping percentage under the pit pressing process should be controlled at 27.86%-35.44%, and the crimping percentage under the confining pressure process should be controlled at 16.01%-22.21%. The temperature rise curves of the two crimping processes have the same change trend. The highest temperature of the cable core appears at the position of the connecting pipe, and gradually decreases along the axial direction. The temperature of the outer surface of the joint shows a downward trend as a whole, but the temperature of the connecting pipe increases in a small range due to the existence of contact resistance.

Polypropylene (PP) insulation is an important development direction of environmentally friendly recyclable cable insulation materials. However, isotactic PP insulation suffers from issues such as high low-temperature modulus, poor toughness, and low elongation at break. Although the introduction of elastomers into PP insulation through blending or copolymerization methods can optimize its mechanical properties, it also leads to a severe decline in insulation performance. For this purpose, this paper reviewed the research progress on strengthening the performance of cable insulation based on chemical grafting modification. At first, we comparatively analyzed the influence patterns and mechanisms of three types of grafting monomers—polar small molecules, high-energy electron/photon-trapping small molecules, and free radical scavenging small molecules—on the dielectric properties of cable insulation, including space charge accumulation, breakdown, and electrical tree degradation, and proposed the optimal method for chemical grafting monomers. Then different grafting modification methods such as solution grafting, melt grafting, solid-phase grafting, suspension grafting, and radiation grafting were compared and analyzed. At last, the problems in the current chemical grafting modification methods for PP cable insulation were summarized, and the development and application of chemical grafting modified PP cable insulation materials were prospected.

To investigate the effects of voltage stabilizers on the insulation properties of crosslinked polyethylene (XLPE) under DC voltage, anthraquinone (EK) was selected as the voltage stabilizer, and XLPE composites with different mass fractions of EK were prepared through physical blending. The impact of different content of EK on the DC insulation properties of XLPE was analyzed by differential scanning calorimetry (DSC) as well as surface potential decay, space charge, and conduction current measurements. The results show that as the mass fraction of EK increases, both space charge accumulation, space charge injection deepth, maximun distortion field strength, and conductivity of XLPE composites decrease at first and then increase. This phenomenon is attributed to the change of the trap distribution characteristics in XLPE by EK. When the mass fraction of EK does not exceed 1%, the deep traps are mainly introduced, which contribute to field homogenization, reduce space charge accumulation, and inhibit carrier migration, thereby decreasing DC conductivity. When the mass fraction of EK is 1%, the improvement effect of XLPE insulation performance is the best.