The researches on the effect of liquid additives on the improvement of processing characteristics and physical properties of crosslinked polyethylene (XLPE) insulation materials for high-voltage cables are insufficient. In this paper, liquid crosslinking agents and antioxidants were taken as research objects. The effects and mechanisms of liquid additives on the scorch resistance, gel content, crosslinking by-products, thermodynamic and dielectric properties of XLPE were discussed. The results show that the liquid cross-linking agent 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane with a high decomposition temperature and long-chain alkyl groups involved in crosslinking reaction can simultaneously enhance the scorch resistance and gel content of XLPE insulation materials, and reduce the content of crosslinking by-products. Meanwhile, the liquid antioxidants α-tocopherol and sorbitol exhibit excellent compatibility, they can form temperature-dependent proton transfer interactions, which can improve the anti-scorch performance of XLPE without compromising its gel content. Additionally, these liquid crosslinking agent and antioxidants can improve the breakdown performance of XLPE insulation while maintaining its thermodynamic properties. This study proves the feasibility of applying liquid additives to XLPE insulation for high-voltage cable.

To study the ablation mechanism of water-blocking buffer layer in high-voltage cable and reveal its critical conditions, the dielectric performance parameters of water-blocking buffer layer material with different water contents were measured. A three-dimensional non-axisymmetric corrugated aluminum sheath structure cable geometric model was constructed based on gravity effects to conduct electro-thermal-flow multi-physics field coupled finite element simulation. Experimental verification was conducted using a constant current simulated ablation test system, and the voltage and temperature variations during the ablation process were monitored in real-time. The results show that poor contact and moisture are necessary conditions for ablation. When the aluminum sheath is poorly contacted with the buffer layer, electric field concentration occurs near the gaps at the well-contacted positions, and partial discharge can be triggered when the moisture content reaches 5%. In well-contacted areas of buffer layer, capacitive current concentration causes localized temperature rise, and the local temperature would reach the ablation initiation threshold at the water content of 25%. According to the experimental results, ablation only occurs when the aluminum electrode is poorly contacted with the buffer layer, while only electrochemical corrosion is observed under good contact conditions. Electrochemical corrosion initially produces high-resistance white powder, followed by partial discharge, which makes the voltage and temperature rise steadily. With the occurrence of partial discharge, the voltage can reach 147 V, and the temperature can reach 187.8℃, causing partial melting of polyester fibers in the buffer layer, further leading to current concentration, and ultimately causing thermal breakdown of the water-blocking buffer layer material.

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.

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 and mechanism of extrusion temperature on the mesoscale crystalline morphology and comprehensive performance of high-voltage cable insulation materials, we prepared three types of insulation materials by controlling the extrusion temperature. Systematic characterization, electrical and mechanical performance testing, and simulation were employed to reveal the structure-property relationship between crystalline morphology and material performance. The results show that at an extrusion temperature of 120℃, the insulation material exhibits densely packed and uniform crystal configuration, and shows optimal crystallinity and crystal size, which is 42.28% and 15.15 μm, respectively. The improvement of crystal morphology can slightly enhance the dielectric constant of insulation materials and maintain extremely low dielectric loss, while can significantly increase the adhesive yield, volume resistivity, electric strength, and elongation at break of insulation materials. According to the mutual verification of simulation and experimental results, it is concluded that complete crystal configuration, larger crystal size and crystallinity can minimize the distortion degree of electric field in the amorphous region, suppressing the occurrence of partial discharge and breakdown, resulting in the electric strength reaching the optimal value (390 kV/mm).

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.

In order to realize the accurate assessment of the ageing state of transformer insulating paper, an ageing state assessing method of insulating paper based on combined assignment and improved TOPSIS was proposed. Firstly, in order to overcome the shortcomings of single feature quantity evaluation, polymerization degree, tensile strength, elongation at break, breakdown voltage, and dielectric loss factor were selected as ageing feature quantities to establish an evaluation system for the ageing state of insulating paper. Secondly, the combined weight value of feature quantities was calculated using the combined assignment model. Finally, an improved TOPSIS model was proposed to construct the Euclidean-gray correlation distance measure. The closeness degree was calculated using the improved TOPSIS model, and the closeness degree interval was set to grade and evaluate the ageing states of insulating paper. The results show that the ageing state assessing method of insulating paper based on combined assignment and improved TOPSIS not only considers the subjective experience weight of experts, but also uses the inherent characteristics of feature quantity data for weight correction, making the weight more scientific and reasonable. At the same time, it compensates for the distance criterion deficiency of the traditional TOPSIS model, making the calculated closeness degree more reasonable. Through the electricity-heat-force combined ageing test, the evaluation method has been verified to determine the ageing states of insulating paper accurately and effectively, and the grading evaluation of ageing states can be achieved by setting a closeness degree interval.

In order to obtain the escape beam characteristics of environmentally friendly insulating gas under the action of nanosecond pulse voltage, the generation laws of the escape electrons in clean air, SF₆, and C₄F₇N/CO₂ gas mixture were studied. An escape electron collection platform was built, and the charge amount of the generated escape electrons was measured when different amplitudes of nanosecond pulse voltages were applied to clean air, SF₆, and C₄F₇N/CO₂ gas mixture under different gas pressures. The results show that the low-energy electrons will accelerate and transform to escape electrons under the action of nanosecond pulse. The higher the nanosecond pulse voltage amplitude, the lower the gas pressure, and the larger the charge amount of escape electrons generated by insulating gas. The clean air has relatively weak inhibition on the generation of escape electrons, and the SF₆ and C₄F₇N/CO₂ gas mixture have obvious inhibition effect on the generation of escape electrons. As the pressure increases, the inhibition effect on the generation of escape electrons of C₄F₇N/CO₂ gas mixture is more obvious than that of SF₆.

C₄F₇N/CO₂/O₂ gas mixture is one of the promising environmentally friendly gas insulation medium to replace SF₆ currently. At present, there is relatively little research on the influence mechanism of the additional buffer gas O₂ and its content variation on the decomposition characteristics of C₄F₇N/CO₂/O₂. In this paper, on the basis of reactive molecular dynamics (ReaxFF-MD) method, a reaction system model of C₄F₇N/CO₂/O₂ gas mixture was constructed to simulate the thermal decomposition process of C₄F₇N gas mixture at different O₂ content and temperature, and the main reaction pathways, product composition and generation rate were analyzed. The results show that the C₄F₇N/CO₂/O₂ gas mixture mainly generates CF₃, CF₂, CF, F, C₂F₅, and CN after thermal decomposition, among them, the generation amount of CF₂ and CF is the highest, followed by CF₃ and F. Although the addition of O₂ to C₄F₇N/CO₂ gas mixture will decrease the initial decomposition time of C₄F₇N, it can effectively reduce the decomposition amount of C₄F₇N and the generation amount of most particles. Especially when the volume fraction of O₂ is 6%, the decomposition amount of C₄F₇N is the least. When the volume fraction of O₂ is 0%-4%, the reaction rate of the main decomposition reaction in the reaction system decreases, while the reaction rate increases when the volume fraction of O₂ is greater than 8%. When the simulation temperature is higher than 2 600 K, the initial decomposition time of C₄F₇N is significantly shortened and the generation rate of decomposed particles is accelerated. The research conclusions provide a theoretical basis for the application ratio optimization of C₄F₇N/CO₂/O₂ and the operation maintenance and diagnosis of its equipment.

C₄F₇N will produce harmful decomposition by-products during discharge or overheating faults, especially C₂F₆ and C₃F₈, which have relatively large amount of production and pose a threat to the safe operation and service life of gas insulated equipment. Therefore, it is necessary to control and handle them. In this paper, the adsorption energy, charge transfer, and adsorption distance of C₂F₆ and C₃F₈ on γ-Al₂O₃(110) surface were studied, and a state density analysis was conducted to evaluate the possibility of γ-Al₂O₃ as a by-product adsorbent. The results show that the γ-Al₂O₃ surface has strong adsorption capabilities for C₂F₆ and C₃F₈, and the adsorption energies reaches -0.5744 eV and -2.819 eV, respectively, showing strong adsorption effects. Particularly, the adsorption configurations at Al sites show higher stability and strong charge transfer phenomenon, indicating that the two gases have strong interaction with γ-Al₂O₃. The state density analysis further confirms that the adsorption of C₂F₆ and C₃F₈ not only alters the electronic states on the γ-Al₂O₃ surface, but also influences its electronic and chemical properties, which provides theoretical support for using γ-Al₂O₃ as a by-product adsorbent for C₄F₇N.