Silicone rubber has excellent mechanical and electrical properties and excellent resistance to high and low temperatures, which is widely used in the field of electrical insulation. In this paper, the effects of extreme ambient temperature on the mechanical and electrical properties of silicone rubber (SR) were reviewed. The crystallization behavior of silicone rubber at low temperature and the methods to improve the thermal stability of silicone rubber were introduced. Finally, the future development trend of silicone rubber was prospected.

Air discharge results from the interaction between electric field and atmospheric environment, therefore the air gap switching impulse discharge voltage is affected by the interelectrode electric field distribution and the atmospheric parameters. In order to calculate the discharge voltage of rod-plane long air gaps at high altitude areas, we construct an insulation prediction model based on k-nearest neighbor (KNN) algorithm with air pressure, temperature, humidity, altitude, and electric field characteristic parameters as feature set. The KNN algorithm was trained by the test data in the altitude range of 55-4 300 m to establish the mapping relationship between air gap features and the insulation strength, and then discharge voltage prediction of rod-plane air gaps at the high altitude of 5 000 m with different gap distances was realized. The maximum relative error and the mean absolute percentage error are 8.58% and 3.78%, respectively, which verifies the effectiveness of the proposed method. When the model was extrapolated to the rod-plane air gaps in plain area under different atmospheric parameters, the predicted discharge voltages also had good agreement with the experimental values. This study results can provide references for the calculation of air gap insulation strength in different atmospheric environment.

This paper focuses on the effect of melt radical graft modification of hindered phenolic antioxidant (AO3052) on the space charge and breakdown properties of polypropylene (PP) insulation. The DC conductivity, space charge distribution, and DC breakdown characteristics of grafted polypropylene with different antioxidant contents were tested and compared with the unmodified polypropylene. The results show that the antioxidants grafting can increase the sensitivity of conductivity to temperature and improve the conductivity activation energy of the samples. The 0.5% antioxidant grafting is effective in improving the space charge accumulation problem and reducing the degree of electric field distortion of PP. The DC electric strength of PP at 90℃ increases by 31.3%, and the ageing electric strength of PP at 90℃ increases by 36.1%, which is attributed to the ability of 0.5% antioxidant grafting in inhibiting the space charge accumulation. The energy band structure analysis suggests that the antioxidant grafting modification can introduce more local energy levels and potential traps in the forbidden bands of PP, which inhibits the charge transport. Meanwhile, the phenolic hydroxyl groups in the hindered phenolic antioxidants can scavenge the free radicals in PP, and the combined effect of the two enhances the breakdown performance of PP.

Moisture intrusion and residual conductive particles are common defects in the joints of tubular insulated busbars in substations. These defects would cause distortion of electric field distribution at the joints, endangering insulation performance and potentially leading to insulation breakdown, burning, and other accidents. In this paper, finite element multi-physics simulation technology was used to construct a joint model of tubular busbar with wrapped insulation material based on the actual structure. Three types of water films, with 10, 30, and 50 mm of lengths, and semi-circular conductive impurities with 0.5 mm of radius, were placed at the interfaces between the metal shielding layer and the main insulation layer, as well as between the main insulation layer and the inner sealing layer. COMSOL software was used to conduct electric field simulation analysis, and the impact of different defects located at various interfaces on the electric field distribution of tubular insulated busbar joint was studied. The results show that both water films and conductive impurities can impact the electric field distribution at the insulation layer interfaces to different degrees. The electric field strength inside the defects decreases, while the electric field strength at the defect edges increases dramatically. Among these, the electric field distortion with conductive particles at the insulation interface is more severe than that with moisture intrusion, making insulation breakdown faults more likely. Therefore, it is crucial to enhance the end sealing and strictly prevent the presence of residual conductive particles.

To address the limitations of traditional methods in accurately detecting micro-defects in epoxy-based insulation, we proposed a novel defect detection method based on photon emission counting analysis under different defect influence. Insulation rod and insulation spacer samples with scratches, surface protrusions, and metal particles were prepared, and their photon counting before partial discharge inception was tested under AC voltage excitation. The results indicate that the average photon counting of samples with severe defects is 12 times higher than that of samples without defects. The photon counting results are significantly influenced by defect types, sizes, position, and insulation gas, and the average photo counting is positively correlated with the defect severity. Therefore, the photon counting can be as a promising tool for early detection of defects in epoxy-based insulation materials.

Polyethylene-based non-crosslinked cable insulation materials have better electrical and mechanical properties, simpler processing, lower energy consumption than XLPE, and can recycle, which are one of the most promising new environmentally friendly cable insulation materials. In this paper, LLDPE/HDPE blending insulating materials with different ratios were prepared using domestically produced base materials, and their electrical, mechanical, rheological, and thermal and oxygen aging resistance properties were tested and compared with the blending materials prepared by imported base materials. The results show that both the domestic and imported blending materials have the best electrical properties and mechanical properties when the mass ratio of LLDPE and HDPE is 7:3. The electrical properties of the domestic blending materials are similar to those of the imported blending materials at the optimal ratio, but the tensile strength is lower. There is a significant difference between domestic and imported blending materials in thermal and oxygen ageing resistance. Through the molecular weight and its distribution test, infrared spectroscopy analysis, it is found that the branching degree of domestic LLDPE is similar to that of imported LLDPE, but its molecular weight distribution range is wider and there is an obvious long-tailed distribution in the direction of low molecules, which may be one of the reasons for the lower tensile strength and antioxidant properties of domestic blending materials.

The application of conventional polyimide in the insulation structure of rail transit traction motors is prone to corona breakdown failure, which seriously affects the reliability and safety of the motor's long-term operation. In this paper, three corona-resistant polyimide materials were prepared by using 4,4′-diaminodiphenyl ether (ODA) as the diamine, pyromellitic dianhydride (PMDA) as the dianhydride, and nano-alumina surface treated with different silane coupling agents as the inorganic filler. The impact of various coupling agents on their surface morphology, mechanical properties, corona-resistant lifetime, and electrical breakdown performance were investigated. The results show that the surface treatment with silane coupling agents can improve the dispersibility of alumina in the polyimide matrix, reduce the agglomeration of nano-alumina, and enhance the corona-resistant properties of the polyimide material, while its excellent mechanical properties are maintained. Among them, the dispersion stability of nano-alumina surface treated with bis-amino silane coupling agent is the best, and the prepared corona-resistant polyimide material also has the best surface morphology and comprehensive performance. The corona-resistant time is 25 min and 120 min, respectively under 3 kV and 2 kV, the tensile strength reaches 167 MPa, and the elongation at break is 29.5%.

To solve the problem that frequency domain reflectometry (FDR) can only distinguish defect polarity and cannot identify the defect length and type, a defect type discrimination method was proposed on the basis of signal attenuation intensity evaluation in this paper. The difference between the total refracted reflection intensity at each defect and the initial reflection intensity was calculated, and then the defect length and type can be discriminated by comparing the magnitude of difference. Combined with the polarity judgment method, the defect can be subdivided into four types. The results show that the method proposed in this paper can successfully identify the length and type of four common defects in cables, including grounding faults, excessive bending, cable body moisture, and long intermediate joints of cables, and the recognition results are consistent with the simulation modeling results. The defect type discrimination method in this paper can identify the common point defects and segment defects in cables.

Epoxy resin has been widely used in the field of insulating materials due to its excellent mechanical properties, thermal stability, chemical stability, and electrical insulation. The stable three-dimensional cross-linked network structure not only gives epoxy resin excellent properties, but also brings great difficulties to its reprocessing, degradation, and recycling. At this stage, more and more researches have begun to focus on the environmentally friendly epoxy resin materials to solve problems such as reprocessing and degradation. In this paper, several typical design ideas and methods of epoxy resin based on dynamic covalent bonds were reviewed, and the environmentally friendly epoxy resin materials through introducting ester bonds, disulfide bonds, silicon-oxygen bonds, imine bonds, D-A structure, acetal bonds, host-guest interaction, and multiple dynamic bonds into the epoxy resin were introduced emphatically. Meanwhile, it is introduced that the topology structure of epoxy resin cross-linked network can be reversibly changed by dynamic covalent bonds under certain stimuli to realize the function of remodeling, reprocessing, self-repairing, and degradation. Finally, the application prospects of insulating materials based on dynamic covalent bonds were summarized and prospected.

In order to more finely evaluate the influence of factors such as the microstructure and material composition of the shed on the macroscopic performance of insulators, the mechanical properties, thermal weight loss, and Fourier infrared spectrum of AC composite insulators with different operating years were tested combined with the molecular dynamic simulation method in this paper. The results show that with the increase of operating years, the tear strength, tensile strength, and elongation at break of the insulator shed from low-voltage end to high-voltage end show a decreasing trend. The content of organic silicone and SiO₂ in the outer layer of shed significantly decrease, which can cause a decrease in macroscopic mechanical properties. In the electro-thermal environment, the bulk modulus, Young′s modulus, and Poisson′s ratio of the shed decrease with the increase of temperature and fluctuate with the increase of electric field strength. The high-voltage end of insulator has the most severe electric field distortion and the worst mechanical properties. The multi-scale model of the composite insulator shed ageing established in this paper can provide a reference for evaluating the ageing state of insulator.