With the miniaturization and light-weighting of electronic equipment, graphite films with high thermal conductivity attract extensive attention. In this paper, a series of nanocomposite films were prepared by copolymerizing p-phenylenediamine (p-PDA) with 4,4′-oxybisbenzenamine (ODA) and 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), and various two-dimensional carbon nanomaterials, including graphene oxide (GO), reduced graphene oxide (rGO), and graphene (GP), were added via mechanical mixing. And then corresponding graphite films were obtained after high-temperature sintering of polyimide films at 2 850℃, the morphology and crystal type of graphite films were analyzed. The results show that graphite films with two-dimensional carbon nanomaterials are flat, they exhibit more flexible, higher degree of graphitization, and larger crystal size, and the lamellar spacing is closer to the ideal graphite. In particular, the horizontal thermal conductivity and vertical thermal conductivity of graphite film containing 2% of GO nanosheets is 1 207 W/(m·K) and 8.38 W/(m·K), respectively. It is concluded that GO nanosheets can induce graphitization of polyimide films under high temperature, and the graphite sheet sintered shows excellent thermal conductivity.

The performance of domestic corona-resistant polyimide film as well as the corona-resistant film magnet wire was compared with that of the similar imported products, and then the reliability of domestic corona-resistant film magnet wire in the application process was discussed. The results show that the conventional properties of domestic corona-resistant film and its magnet wire are comparable to those of similar imported products, and the corona resistance performance and initial partial discharge voltage of domestic corona-resistant film magnet wire are better than those of similar imported products. Domestic corona-resistant film magnet wire has excellent manufacturability in the coil forming process, which meets the technical requirements of inverter traction motor applications.

In this paper, the aggregation properties of molecular chain as well as permittivity of 10 kinds of polyimides containing carbonyl group or sulfone group were characterized. Moreover, microscopic parameters such as theoretical density, free volume fraction, polarizability density, and dipole moment density were calculated based on density functional theory (DFT) and molecular dynamics theory (MD). The results show that the partially crystallized polyimides show relatively high theoretical density and low free volume fraction (FFV), which indicates that the measured results are in good agreement with the theoretical calculations. Compared with using polarizability density, using dipolar moment density, which is highly correlated with the orientation polarization, provides a more accurate prediction of the size of the polyimide dielectric constant in relation to the molecular structure in tests in the frequency range of kHz .

In the life evaluation of polyimide (PI) film modified by nano TiO₂, a small sample insulation life evaluation method based on gray neural network was proposed to solve the problems such as lack of failure data, life distribution cannot be determined uniquely, high cost, and long test time. Nano TiO₂ modified PI film was prepared by in-situ polymerization method, and the accelerated electrical ageing test was conducted on the films to obtain the failure data. The grey neural network was constructed and trained to obtain the extended data with the similar characteristics and changing rules with the original data. The least square method was used for parameter estimation, and the life evaluation results of different failure data samples, distribution models, empirical cumulative failure functions were analyzed and compared. The different life evaluation schemes before and after extending were analyzed by calculation example. The results show that the combination of Weibull distribution and mathematical expectation formula is more suitable for life evaluation of original sample size.The evaluation of insulation life using expanded failure data has a better effect, and the combination of inverse power function model, lognormal distribution, and median empirical formula is the most suitable for the life evaluation of the extended samples.

In order to further clarify the key properties of matrix resin in semiconducting shielding materials, three different types of semiconducting shielding materials at home and abroad were selected, and their microstructure characteristic, mechanical properties, electrical properties, and rheological properties were tested. The results show that the volume resistivity of each shielding material is low, and the temperature stability of resistivity is good. The acrylate content of the imported shielding material matrix resin is higher, polarity is greater, and the mechanical toughness is better. At the same time, the pseudoplasticity of the imported shielding material is stronger. In a certain shear rate range, the viscosity of the material can be reduced by increasing the shear rate appropriately, and the energy consumption can be reduced by increasing the fluidity, and then the production efficiency can be improved. Based on the results of the experimental analysis, the polarity or ester content of the material is proposed as a key parameter to reflect the matrix resin in the semiconductive shielding material.

Biaxially oriented polypropylene (BOPP) film is a mainstream dielectric material used in power capacitor, there is still a large gap between thermal stability performance of imported BOPP films and that of domestic films. In order to systematically investigate the thermal stability of domestic and imported BOPP film, as well as to reveal the thermal ageing mechanism, we selected typical domestic and imported BOPP film samples, and conducted vacuum thermal ageing test on them for 1 000 h under 80℃ and 120℃, respectively. The changing law of molecular structure, aggregation structure, and electrical properties of the films before and after thermal ageing was compared and analyzed via infrared spectroscopy (FTIR), optical microscope observation, X-ray diffraction (XRD), dynamic thermomechanical analysis (DMA), dielectric spectroscopy, and direct current breakdown strength. The results show that compared with that of imported BOPP films, the crystallinity of domestic films is lower and the force between molecular chains is weaker. The breakdown field strength of domestic films is 5.7% lower than that of imported films. Under the effect of long-term thermal ageing, both BOPP films have undergone recrystallization, including the increase of crystallinity and lamellae size in the crystal region and the increase of free volume and the molecular chains loss scale in the amorphous region. Meanwhile, the change of the aggregate structure leads to the increase of the dielectric loss and the decrease of the breakdown strength at low probability zone of the film after ageing. Moreover, compared with domestic films, the stronger inter-chain forces in imported films effectively inhibit the recrystallization process, and decrease the generation and development of electrical weakness, which makes the imported BOPP films have better long-term thermal stability.

Epoxy resin micro-alumina composite materials with micro-alumina mass fraction of 0, 20%, and 40% were prepared. The effect of micro-alumina filler on the dielectric relaxion behavior of epoxy resin at high temperature was analyzed by dielectric test at room temperature and high temperature and fitting calculation of high temperature dielectric spectra. The results show that the effect of micro-alumina on the dielectric relaxion at high temperature is more obviously than that at room temperature. With the introduction of alumina, the optical frequency dielectric constant increases, while the relaxation strength of relaxion process α shows little change. With the increase of mass fraction of filler, the relaxion time of relaxion process α decreases. Besides, the micro-alumina filler significantly increases the relaxion strength of relaxation process δ. However, with the increase of mass fraction of micro-alumina, the relaxation strength of relaxation process δ decreases, while the relaxation time increases continuously.

In order to study the effect of silane coupling agent modification on the thermomechanical and dielectric properties of SiO₂/PI composite and its internal mechanism, we established the composite model of pure PI, SiO₂/PI and SiO₂/PI with 6% and 12% of the grafting density of silane coupling agent on the surface of SiO₂. The solubility parameters, interaction energy, glass transition temperature, Young's modulus, shear modulus, mean square displacement, free volume fraction, relative permittivity, and dielectric strength of the four models were calculated. The results show that the silane coupling agent modification significantly improves the thermomechanical and dielectric properties of the composite material, and the graft density has an obvious effect on the modification effect. The SiO₂/PI composite system with 6% of grafting density of silane coupling agent has the best thermomechanical properties, while maintains a lower relative permittivity and a higher dielectric strength. In addition, the two systems grafted by silane coupling agent have smaller free volume fraction and mean square displacement, as well as larger solubility parameters and interaction energy. It is indicated that limiting the movement of molecular chains and improving the compatibility between SiO₂ and PI matrix are the keys to improving the thermomechanical and dielectric properties of composite materials.

In order to explore the correlation between the aggregation structure of biaxially oriented polypropylene (BOPP) film and its breakdown property, and promote the localization of BOPP, the properties of four kinds of BOPP samples manufactured at home and abroad were compared by optical observation, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), impregnation, and DC breakdown experiments. The results show that the BOPP film with higher crystallinity and higher segment activation energy has a larger electric strength. Impregnating the BOPO film with benzyl toluene can change its aggregation structure and improve the electric strength of electrical weak point. Compared with similar international products, domestic BOPP films show the gap of low electric strength, small shape parameters, and many electrical weak point.

Hindered phenolic antioxidant is a main antioxidants commonly used in cross-linked polyethylene (XLPE) insulation to improve its processability and long-term electrical performance. In order to discuss the effect of hindered phenolic antioxidants on the DC breakdown behavior of XLPE insulation deeply, two kinds of XLPE insulation samples containing different multi-hindered phenolic antioxidants were prepared, and their properties were measured. The results show that the addition of hindered phenolic antioxidants can obviously improve the electric strength and breakdown stability of XLPE insulation, this is because the addition of hindered phenolic antioxidant can introduce deep traps into XLPE insulation and increase the trap density. However, the energy levels and types of deep traps introduced by the two multi-hindered phenolic antioxidant are different, therefore the effects of them on the improving the electric strength of XLPE insulation are different. In addition, the addition of hindered phenol antioxidant can improve the crystallinity and crystallization uniformity of XLPE, but the effect is not obvious.