Aiming at the electrical tree degradation and discharge breakdown of cross-linked polyethylene (XLPE) insulation for high-voltage cables, we prepared XLPE composite materials using photon-trapping voltage stabilizers, including two trifunctional triazine compounds (1,3,5-triallyl cyanurate (TAC) and triallyl isocyanurate (TAIC)) and two hydrogen-capturing phenyl ketones (4-methyl diphenyl ketone (MBP) and 4,4′-di-chlorobenzophenone (DCBP)). The influence rule of photon-trapping voltage stabilizers on the electrical tree degradation of XLPE composite materials was studied, and the photon trapping and excitation properties of the aromatic photon-trapping compounds, and their chemical reaction pathways were analyzed. The inhibition mechanism of the additive types on the electrical tree degradation was explored by using quantum chemical calculations. The results show that the addition of DCBP and TAC with the mass fraction of 1% can increase the initial voltage and initiation time of electrical tree in XLPE insulation. Compared with the pure XLPE insulation under the same voltage, the electrical tree length of DCBP/TAC/XLPE composite insulation decreases by 16.3%, the cumulative damage area decreases by 72.8%, and the maximum amplitude of partial discharge decreases by 29.7%, which shows the best partial discharge suppression and resistance to electrical trees. According to the quantum chemical calculations, MBP and DCBP have strong photon absorption properties, and DCBP can absorb photons with a wavelength of 334 nm, demonstrates a higher reactivity than MBP, and is more capable of capturing photons generated by partial discharge to hinder the damage of photons on the XLPE molecular chain. According to the reaction pathway analysis, DCBP molecure enters excited state after capturing photons, which triggers the proton transfer within the XLPE molecular chains, and promotes the free radical cross-linking reaction between TAC and PE molecular chain, thereby enhancing the local stability of the molecular chain and inhibiting the electrical tree deterioration of XLPE insulation.

To investigate the influence of water on the breakdown position of oil-filled cable terminal, this study simulated and analyzed the failure reason caused by water in the 220 kV oil-filled cable terminal. A cable test platform was established in the laboratory, and the influence of the grounding state and electric field strength on the breakdown position was simulated. The partial discharge (PD) quantity and water film height of the cable in different grounding states and at different electric field strength were recorded by using high frequency current partial discharge detector and camera. The results show that the water content in oil, grounding state, and electric field strength are the important factors affecting the fault location of oil filled cable terminal. When the water is immersed in the cable terminal and reaches a certain amount, and the cable terminal is directly grounded, the higher the electric field strength, the more water molecules escape from the oil-water interface, the higher the water film height, the longer the distance between the breakdown point and the upper surface of stress cone, and the larger the partial discharge. The intensity of PD is positively correlated with water film height, and the silicone oil degradation defects within the cable terminal can be evaluated by partial discharge, which provides a reference for evaluating the insulation status of oil-filled cable terminal.

The aggregate structure, microcrystalline structure, and surface chemical properties of domestically developed conductive carbon black (CB) were compared with that of international commercial products, and the comprehensive performance of semi-conductive shielding materials prepared by filling CB were studied. The results show that the domestic CB exhibits comparable aggregate structures, microcrystalline dimensions, and carbon content with the imported CB, while the domestic CB contains 0.51% of sulfur elements and demonstrates lower particle size uniformity, alongside a significant variance in the content of various surface functional groups. The semi-conductive shielding material prepared with domestic CB achieves equivalent electrical and mechanical performance to that prepared with imported CB, but its surface smoothness is inferior, which does not meet the industry requirements. It is concluded that the uniformity of particle size, contents of surface functional groups, and the sulfur content are important research direction for structural optimization and performance improvement of domestic conductive carbon black, and surface smoothness is a significant research focus for the development of domestic high-voltage semi-conductive shielding materials.

Local abnormal heating often occurs in the heat-shrinkable terminals of medium-voltage cables, leading to localized overheating and accelerated ageing of cable insulation, which even causes premature insulation failure. To elucidate the causes of abnormal heating in medium-voltage cable heat-shrinkable terminals, the electric-thermal field of cable heat-shrinkable terminals under various typical fault conditions was simulated by electromagnetic-thermal coupling. The results show that during the long-term operation of the cable, the ageing of the stress control tube leads to localized temperature rise in the insulation. The more severe the ageing, the higher the temperature rise. Furthermore, when the outer surface of the terminal becomes contaminated due to dust accumulation and moisture, a significant hot spot forms near the break of the outer semiconductive layer; however, the hot spot diminishes when the contamination layer is far from the break. Further analysis on the thermal field distribution of the terminal with moisture on the stress control tube reveals that hotspots only appear when the inside of tube is moist. A thermal circuit model considering internal defect hotspots was built, and temperature inversion was implemented to monitor the highest temperature point at the internal insulation interface of heat-shrinkable terminal. It is verified that the method is effective.

To investigate the ageing characteristics and lifetime evaluation methods of graft-modified polypropylene cable insulation materials, accelerated thermal ageing tests were conducted on the samples at different temperature, and the changes in electrical and physicochemical properties of graft-modified polypropylene cables at various ageing stages were studied. The variation of key characteristic parameters, such as melting temperature, relative dielectric constant, and elongation at break with ageing time was analyzed. The results show that the melting temperature, electric strength, and elongation at break are significantly correlated with ageing time, and these parameters can be used as effective indicators for assessing the ageing degree of graft-modified polypropylene cable insulation materials.

Perfluoroisobutyronitrile (C₄F₇N) has excellent eco-friendly and insulation properties, and is the mainstream environmentally friendly gas to replace SF₆ gas. In this paper, a series of power frequency AC corona discharge experiments were conducted on C₄F₇N/CO₂ gas mixture by needle-plate electrode, and then the influences of different electrode materials (stainless steel, aluminum, and brass) and applied voltages on the decomposition characteristics of C₄F₇N/CO₂ gas mixture were analyzed based on gas chromatography/mass spectrometry. The results show that the contents of the characteristic decomposition gases of C₄F₇N/CO₂ gas mixture increase with the increase of applied voltages, and are obviously affected by the chemical activity of metal materials, among them, the total amount of decomposition products under aluminum electrode is the highest. The content ratios of characteristic decomposition gases, that is c[C₂F₆]/c[CF₄] and v[C₂F₄]/v[C₃F₆], have good recognition degree for electrode materials and corona discharge degree.

C₆F₁₂O has good environmental protection characteristics and insulation properties, and has good application prospects in medium and low voltage gas-insulated equipment. In order to explore the influence of micro-water inside the gas-insulated equipment on the insulation performance and decomposition characteristics of C₆F₁₂O/CO₂ gas mixture, a gas power frequency breakdown test platform was set up, and the breakdown voltage of 4%C₆F₁₂O/96%CO₂ gas mixture under 0.14 MPa pressure within the range of 0-1 000 μL/L micro-water concentration was studied.The influence of different micro-water concentration on the power frequency breakdown characteristics of gas mixture was analyzed. The types and concentrations of the decomposition products of C₆F₁₂O/CO₂ gas mixture were analyzed quantitatively and qualitatively by gas chromatography-mass spectrometry (GC-MS) after breakdown, and the influence laws of micro-water concentration on the concentration of breakdown decomposition products and effective gas production rate were obtained. The results show that micro-water will reduce the power frequency breakdown voltage of C₆F₁₂O/CO₂ gas mixture. The main breakdown decomposition products of C₆F₁₂O/CO₂ gas mixture are CF₄, C₂F₆, C₃F₆, C₃F₈, C₃F₇H, CF₂O, C₄F₁₀, C₅F₁₂, and CF₃H, among them, the concentration and effective gas production rate of CF₄, C₂F₆, and C₃F₇H are positively correlated with the micro-water concentration, and the concentration of CF₄, C₂F₆, C₃F₆, C₃F₈, and C₃F₇H are positively correlated with the breakdown times. Considering the insulation performance and decomposition characteristics, it is recommended to strictly control the concentration of micro-water inside the C₆F₁₂O/CO₂ gas mixtures equipment during engineering application, and increase the test frequency of micro-water in the equipment.

In order to assess the feasibility of using C₅F₁₀O/dry air gas mixture to replace existing dry air or nitrogen in insulation equipment under low partial pressure conditions, we analyzed the insulation performance of C₅F₁₀O/dry air gas mixture systematically. The results show that in a quasi-uniform electric field, when the partial pressure of C₅F₁₀O is 5-10 kPa, the insulation strength of the C₅F₁₀O/dry air gas mixture is 1.1-1.9 times and 1.4-2.3 times bigger than that of dry air and nitrogen under the same condition, respectively, which indicates that even at low partial pressures, the C₅F₁₀O/dry air still demonstrates strong insulation performance and has technical advantages compare to dry air or nitrogen. Furthermore, the C₅F₁₀O/dry air shows good stability in multiple breakdown tests, and the slope of fitting curves between breakdown voltage and breakdown times approaches zero, indicating that its insulation performance has not significantly deteriorated.

In this paper, the research progress on new eco-friendly insulating gases at home and abroad was reviewed, and the international mainstream promotion of perfluoroisobutyronitrile (C₄F₇N) gas and its application in electrical equipment were expounded emphatically. The gap and surface insulation characteristics of C₄F₇N gas mixture were summarized, and the design criteria of the related equipment insulation was proposed. The decomposition characteristics and gas-solid compatibility evaluation indices of C₄F₇N gas mixture under different operating conditions were analyzed. Additionally, the research progress on arc-quenching performance of C₄F₇N and its gas mixture and the development and application of a series of eco-friendly equipment were introduced, so as to provide a theoretical reference for the environmental protection upgrade of SF₆ electrical equipment in the current stage. Meanwhile, it was noted that the research and development efforts on new eco-friendly insulating gases with superior performance were still ongoing at home and abroad, which can provide technical support for the construction of a green and low-carbon power grid.

Firstly, the physico-chemical characteristics of the decay-like core rod were analyzed, and the effect of decay-like on the mechanical properties of the core rod was studied. And then, the vibration modes of composite insulator core rods were analyzed by simulation, and the relationship between characteristic frequency and the decay-like degree was studied. Finally, a vibration excitation detection method was proposed for decay-like composite insulator, and the characteristic frequencies of the 110 kV composite insulators with different degrees of decay-like defects were measured and analyzed. The results show that the complete degradation of epoxy resin and the hydrolysis and pulverization of glass fibers in the core rod make the decay-like region loss mechanical properties, leading to the decrease in the overall stiffness, tensile resistance, and deformation resistance of the core rod. Compared with the intact core rod, the characteristic frequencies of 3-5 order vibration mode of decay-like core rod decrease by 2.8%-14.3%, the decreasing range of characteristic frequencies of higher order vibration modes decrease more obvious, and the decreasing range increases with the increase of decay-like degree. The decay-like detection method based on vibration mode can diagnose the decay-like degree of composite insulator, and also can reflect the changes of its mechanical properties, which is suitable for non-destructive detection of decay-like in composite insulators.