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.

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 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).

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.

This paper proposed a defect assessment method for high-voltage XLPE cable based on a multi-scale correlation feature fusion convolutional neural network. On the basis of a data-driven approach, this method established the potential relationship model between characteristic gas concentration and defect type by training a convolutional neural network, thereby diagnosing the cable defects based on characteristic gas concentration. Firstly, simulated data were obtained using a data augmentation technique based on mean shift. Then, a 1D convolutional neural network based on multi-scale correlation feature fusion was designed. Finally, the training and defect identification were carried out on the basis of simulation data by using the convolutional neural network. The results show that the method on the synthetic data test set and the real basic data achieves defect recognition accuracies of 92% and 88%, respectively. It is indicated that the proposed method can effectively utilize characteristic gas concentration to diagnose cable defects.

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.

Heptafluoroisobutyronitrile (C₄F₇N) has excellent insulation properties and low greenhouse effect, and is currently the mainstream environment-friendly gas used for electrical equipment insulation. Because of the large differences in physical and chemical properties between C₄F₇N and SF₆, the current SF₆ detection technology and equipment can not meet the application requirements of C₄F₇N gas mixture. In this paper, the detection method of C₄F₇N/CO₂ gas mixture was studied by referring to the live detection technology of SF₆ gas in operating equipment. The field detection schemes were proposed, which included using gas chromatography to detect purity and composition of gas based on high-precision helium ionization detector, using thermal conductivity principle to detect C₄F₇N ratio, using resistance capacitance sensor method to monitor micro-water content, and using non-spectral infrared technology combined with Lambert-Bill rule to quantitatively monitor gas leakage fault, and the corresponding detection devices were developed to carry out the detection and verification test for gas state. The results show that all detection schemes have high detection accuracy and can support the operation and maintenance testing and field application of C₄F₇N environment-friendly electrical equipment.

Regarding the internal carbonization creepage defect of composite insulator, a finite element model of electromagnetic and thermal coupling calculation for FXBW-500 large-small-small shed type composite insulator was established, and the influencing laws of defect location and surface pollution on the temperature rise caused by internal carbonization creepage defect in core rod were analyzed. The results show that when there is a local carbonization creepage defect at different positions of composite insulators, the local temperature rise from high to low is high voltage end, low voltage end, and middle end. When there is pollution, the temperature distribution of the carbonization creepage defective insulator does not change significantly, but the maximum temperature rise values of each part all increase significantly, among which the maximum temperature rise of high voltage end increases from 9.3℃ to 18.2℃, and the temperature rise along the surface increases from 2.52℃ to 4.94℃. Although the existence of pollution makes the overall temperature of the insulator rise, it still does not conceal the temperature jump at the defect location. Therefore, when the location of carbonization creepage defects are identified through temperature, the temperature jump can be taken as a reference.

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.

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.