High thermal conductive insulating materials are key functional materials for achieving efficient heat dissipation in motors, which is of great significance for improving the operational stability and prolonging the service life of motors. This article briefly described the thermal conductive modification mechanisms of insulating materials,reviewed recent research progress on high thermal conductive insulating varnish, mica tapes, films, and potting compounds used in motors, discussed their current application status in the field of motors, and further provided an outlook on future research direction.

During the laying process, excessive lateral pressure and traction would cause mechanical damage to cables, leading to severe failures such as sheath grounding, overheating, insulation breakdown, and combustion during operation. This paper summarized the research progress on traction and lateral pressure of land cables, including their generation processes and effects on cable insulation structures and materials, calculation methods, monitoring, and online control techniques of traction and lateral pressure. The influence of mechanical stress on microscopic characteristics such as crystal size, crystallinity, and trap number and depth in cable insulation materials was discussed in detail, and the failure mechanisms of cable materials under mechanical stress were analyzed. Regarding the calculation methods for mechanical stress, the shortcomings of current approaches were summarized, and future research directions for cable mechanical stress were outlined.

With the development of power electronic equipment toward high-frequency, miniaturization, and integration, the performance of traditional polypropylene (PP) film materials is gradually becoming insufficient to meet the requirements of modern capacitors for high electric strength, low dielectric loss, and long service life. To address this, the modified PP film materials with different grafting rates were prepared by grafting 4-methylstyrene onto polypropylene (PP) via an aqueous suspension grafting method, and the effect of grafting rate on their comprehensive properties was studied. The results show that the optimal swelling time and reaction time of grafting modification are 120 minutes and 150 minutes, respectively. With the increase of grafting rate, the heating melting curve tends to shift towards lower temperatures, while the cooling crystallization curve tends to shift towards higher temperatures. When the grafting rate is 0.88%, the modified PP exhibits the highest tensile strength and elongation at break, with the electric strength reaching a maximum value of 400.8 kV/mm, and the trap density reaching a maximum value of 9.52×10¹⁹ m^-³·eV^-1, which is nearly 3.8 times higher than the maximum trap energy level density of pure PP material.

This paper investigated the generation laws of characteristics gases at the cross-linked polyethylene-silicone rubber insulation interface of cable accessories under different types of discharge faults, and proposed gas diagnostic criteria for discharge fault types at the cable accessory interface based on this. Firstly, a gas generation experimental platform for insulation interface discharge of cable accessories was established, different types of discharge faults were distinguished by the high-frequency current transformer method, and the characteristics of the escaping gases from insulation interface discharge faults were analyzed by gas chromatography. Then, a real-type discharge fault gas generation platform of cable accessory was built to experimentally verify the generation laws of characteristic gases under interface discharge faults. Finally, the diagnostic criteria for discharge faults in cable accessories were proposed based on characteristic gas formation laws. The results show that the insulation interface mainly generates H₂, CO₂, CO, CH₄, and C₂H₆ under low-energy discharges (partial discharges), while additionally produces C₂H₄ and C₂H₂ under high-energy discharges (arc discharges). Based on this, a comprehensive gas diagnostic criteria is proposed: when the concentration ratio of CO to CO₂ is between 0.10 and 0.69, it is considered as low-energy discharge; when it is greater than 0.70, it is considered as high-energy discharge. Only the first five gases are present in the gas composition, it is considered as low-energy discharge; while both C₂H₄ and C₂H₂ are detected, it is considered as high-energy discharge. Quantitative indicators show that the proportion of unsaturated hydrocarbons in high-energy discharges ranges from 0.07 to 0.16, and the concentration ratio of unsaturated hydrocarbons to H₂ ranges from 0.08 to 0.30.

Aiming at the problem of electric field distortion and abnormal temperature rise caused by insulator degradation in DC transmission system, a distributed conductance matrix was constructed based on the multi-conductor system theory, and the distributed conductance characteristics and electric field distribution of U550BP/240T porcelain insulator string under DC voltage were studied by electric field simulation. The heating mechanism of insulator string was revealed by thermal-electric coupling model and DC live test. The results show that the distributed conductance between normal insulators is basically equal, about 15×10^-10 S/m, while the conductance between the fittings of zero-value insulators increases sharply to about 108×10^-10 S/m. The distributed conductance between fittings and conductors, as well as between fittings and ground, decreases with the increase of spatial distance. The voltage along the insulator string shows a U-shaped distribution. For the zero-value insulator, the partial voltage drops to 1.4%-1.6% of the total voltage, and the peak value of axial field strength attenuates to 5.5%-7.1% of the normal value, resulting in a significant rise in the field strength and partial voltage of the adjacent insulator. Through the 120 kV DC live test, it is verified that the heating curve along the string is similar to the U-shaped distribution curve of voltage, which verifies that the voltage plays a leading role in the heating of insulator. The iron caps of zero-value insulators exhibit uniform heat generation, while those of normal insulators show a significant temperature rise in the middle and lower parts. The correlation coefficient between the heat generation characteristic curves of the insulator string obtained from simulation and experiment is greater than 0.95%, with a maximum error of 12.38%, which verifies the decisive role of distributed conductance in the electric field distribution and heating of insulator, and can provide theoretical basis for the state monitoring of insulators in DC system.

To study the interface ageing characteristics of hybrid porcelain insulator, the hybrid porcelain insulators, type A and type B composite porcelain insulator were conducted 1 000 h water-boiling ageing test, and the leakage current, infrared temperature rise, and bonding property of the aged samples were measured. The interface bonding mechanism of the hybrid porcelain insulator was analyzed through porcelain block simulation. The results show that during the water-boiling process, the leakage current of the hybrid porcelain insulator changes slightly and no temperature rise occurs, the bonding property is CC-5 level, and the anti-ageing performance of the interface is good. The simulation test show that after coating the silane coupling agent, the surface roughness of the porcelain increases by 821.4%, and the formation of Ti-O-Si chemical bond enhances its physical interlocking with the silicone rubber. At the same time, more -OH groups appear on the surface of porcelain block, which can better chemically bond with silicone rubber, achieving good interface bonding effect.

In order to evaluate the thermal ageing of silicone rubber for cable intermediate joint insulation layer, this paper proposed an evaluation method based on nonlinear ultrasonic signal characterization. Firstly, a ultrasonic detection simulation model of silicone rubber ageing was established, and tests were conducted on the real cable joint specimens with different thermal ageing time at 200℃. Then the nonlinear ultrasonic detection was carried out at typical positions by using wedge coupling method. Lastly, the correlation between the ageing time and ultrasonic nonlinear coefficient was verified and the mechanism was explored. The results show that the experimental and simulation results are highly consistent in the change trends of the characteristic parameters of transmitted wave signal in time-domain and frequency-domain. Specifically, as the ageing time increases, the fundamental wave amplitude and the second harmonic amplitude both gradually decrease, and the ultrasonic nonlinear coefficients gradually increase. Under actual ageing time of 480, 720, and 960 h, the relative errors between the ageing time of silicone rubber obtained by substituting the nonlinear ultrasound coefficients obtained from the experiment into the fitting relationship equation and the actual ageing time are 1.58%-5.66%, 2.57%-6.66%, and 0.85%-4.75%, respectively, and the consistency between the fitted results and the actual ageing time is better, which verifies the validity of nonlinear ultrasonic testing method in the assessment of thermal ageing damage of silicone rubber.

The 1 100 kV bushing at the grid side of converter transformer in the converter station commonly adopts oil-impregnated paper capacitive bushing technology, which has prominent issues with abnormal gas production, prone to oil leakage and internal discharge failures. In order to improve the safety and reliability of 1 100 kV grid side bushings, we designed an epoxy resin impregnated paper capacitive bushing at the grid side of converter transformer. Firstly, the insulating materials, insulation structure, insulation coordination, and manufacturing processes of the bushing were studied. Secondly, the theoretical design of the bushing capacitive core was completed, and the designed product was simulated and analyzed using the finite element method. Finally, the prototype was produced and type tests were conducted. The results show that the simulation results of electric field distribution, hot-spot temperature, and mechanical stress of the newly developed 1 100 kV epoxy resin impregnated paper capacitive bushing all meet the application requirements, with an improvement of 3% in electric field safety margin. This bushing has successfully passed the type tests according to domestic and international standards, and all assessment indicators meet expectations.

This paper aims to investigate the application effect of two-component polyurea materials in enhancing the insulation strength of transmission line conductor gaps. Firstly, the physicochemical and electrical properties of the two-component polyurea materials were characterized systematically. On this basis, an experimental platform simulating transmission line conductor gaps was constructed, and the effects of coating thickness and gap distance on the breakdown characteristics of the conductor gaps under 50 Hz AC voltage were analyzed systematically. The results show that the glass transition temperature of the two-component polyurea materials is 152℃, exhibiting good thermal stability, the characteristic electric strength reaches 26.21 kV/mm, the tensile strength is 20.2 MPa, and the elongation at break is 515.2%, and it also shows excellent resistance to UV ageing. When the coating thickness is thin (1 mm and 2 mm), the enhancement effect of polyurea materials on the breakdown voltage of transmission line conductor gaps is limited. However, as the coating thickness increases to 3-5 mm, the breakdown voltage of conductor gap increases significantly. In particular, when the gap distance is 20 cm, as the polyurea coating thickness increases from 0 mm to 4 mm, the characteristic breakdown voltage of conductor gap increases from 138.43 kV to 160.94 kV, showing a significant improvement. When the coating thickness reaches 4 mm or more, even if the minimum withstand gap distance shorten to below 3 cm, the polyurea coating still does not breakdown, demonstrating excellent voltage resistance.

In order to evaluate the application potential of environmentally friendly polypropylene materials in high-voltage cable accessories, the electrical properties include electric strength, space charge distribution, and polarization current of novel polypropylene insulating material and silicone rubber under typical operating conditions were studied to assess their voltage withstand capability, charge accumulation behavior, quasi-steady-state polarization current. At the same time, a 110 kV cable joint simulation model was established using finite element simulation software to simulate the electric field distribution at the joint, and the application performance of polypropylene/silicone rubber composite insulation in high-voltage AC cable joints was explored. The results show that the novel polypropylene exhibits excellent electric strength, although the electric strength decreases with the increase of temperature, it still remains 88.80 kV/mm at 90℃. The electric strength of the polypropylene/silicone rubber composite insulation is primarily influenced by the silicone rubber, but it exhibits good thermal stability and maintains 39.70-47.01 kV/mm within 30-90℃. Space charge test reveals that the polypropylene still has significant charge suppression ability under 20 kV/mm, which can effectively improve the electric field distortion at the composite interface. Calculation based on simulation model indicates that the internal electric field distribution in the 110 kV cable joint using this composite insulation is reasonable, and the maximum electric field strength at the polypropylene/silicone rubber interface is only 5.7 kV/mm, which is far lower than its electric strength. The research has confirmed that the reliability of the novel polypropylene/silicone rubber composite insulation structure meets the operational requirements of high-voltage cable joints.