In order to solve the problem of blank cracking in the pressing process of special-shaped nozzle, we designed a near-clean forming special-shaped nozzle pressing mold independently, and optimized the structure of the mold gradually. At the same time, the process parameters such as pressing pressure, pressing speed, and holding time were optimized based on the existing pressing process. The results show that, through the gradual optimization of the structure of the special-shaped pressing mold, the cracking problems of the arc transition area and the bottom of the V-shaped pad of the nozzle were solved. Through the optimization of the pressing process, the density consistency of each position of the nozzle blank is improved, the mechanical and electrical properties of the arc transition area have little difference with those of the two ends, and the raw material loss of the nozzle pressed by this process is reduced by about 30%.

Large generators are affected by factors such as thermal stress during operation, resulting in deterioration or even failure of stator bar insulation, which affects the safe and stable operation of the generator. In order to clarify the effectiveness of the polarization and depolarization current (PDC) method for evaluating the main insulation performance of stator bars, at first, PDC method was used to evaluate the main insulation performance of stator bars in the thermal ageing state. According to the PDC test results, the basic characteristic parameters such as the steady-state conductance current, 0.1 Hz polarization/depolarization loss, and asymmetry coefficient were extracted. Then, singular value decomposition (SVD) algorithm was used to analyze the PDC data of the bar sample with the extended Debye model, and the branch number and branch parameters of its analog circuit were obtained. Through analysis, the change regulation of the above characteristic parameters during ageing was clarified. Finally, Fourier transform infrared spectrum (FTIR) analysis was conducted on samples with different thermal ageing durations to further clarify the mechanism of post-insulation curing and degradation from a microscopic perspective. The results show that as the degree of insulation ageing intensified, the steady-state conductivity current and 0.1 Hz polarization/depolarization loss increases, the degree of asymmetry coefficient deviation from 1 intensifies, and the interface polarization time constant τ₂ decreases.

In order to obtain the location information of defects in buffer layer of HV cable, at first, according to the surface morphological characteristics of buffer layer, the buffer layer states were devided into dry state, damp state, corroded state, and corroded-ablative state, and the change law of volume resistivity and relative dielectric constant during the development of defects from dry state to corroded-ablative state of buffer layer was studied via thin slice samples. Then the computing formula of the distributed capacitance and distributed conductance in the network of HV cables transmission line was derived. The feasibility of applying the FDR method to locate defects in the buffer layer of HV cables was also evaluated. Finally, a long cable experimental platform was built in the laboratory to study the effectiveness of the FDR method in locating buffer layer defects. The results show that the development of buffer layer defect mainly affects the distributed capacitance, and impedance discontinuity points generate in the process. FDR can locate the moisture and defects of the buffer layer, but the further distinction between corrosion defects and ablation defects needs to be combined with other state detection methods.

In order to further explore the application potential of C₄F₇N/CO₂ mixed gas in high-voltage electrical equipment, a preparation system for C₄F₇N/CO₂ mixed gas was established and mixed gas with different volume fraction of C₄F₇N was prepared by partial pressure method. A gas chromatograph-hydrogen flame ionization detector (GC-FID) detection method was established, in view of the difficulty in controlling the testing quality during the preparation of C₄F₇N/CO₂ mixture system, the thermal driven diffusion simulation experiments of different C₄F₇N/CO₂ mixed gas was carried out based on fluid mechanics and finite element analysis. The results show that when the volume fraction of C₄F₇N is 2%, 5%, and 10%, the diffusion equilibrium time of C₄F₇N/CO₂ concentration is 4 775 s, 6 600 s, and 8 800 s, respectively; the concentration diffusion equilibrium time of C₄F₇N gas is 94 min, 122 min, and 158 min, respectively. The three C₄F₇N/CO₂ mixed gas can achieve good quality control effect in the quality detection and application after preparing for 100 min, 125 min, and 160 min, respectively.

At present, there is a lack of effective liquid repair materials for ablation defects in the buffer layer of high-voltage cables, resulting in the inability to timely and effectively eliminate the hidden dangers of ablation defects in high-voltage cable lines. In this paper, acrylic based buffer layer ablation defect liquid repair materials were prepared and repair experiments were conducted on actual ablation defects in cable buffer layer. The repair effect of carbon black content in repair solution on the electrical properties of the buffer layer was studied. The results show that when the mass fraction of carbon black in the repair solution coating is 20%, the volume resistivity of the repaired buffer layer decreases to the level of new buffer layer and basiclly remains unchange with temperature. Based on the characterization of micro morphology, it is analyzed that the repair solution forms a carbon black coating on the fiber surface of the buffer layer, covering the original uneven coating and non-conductive particles. At the same time, the continuous water blocking powder layer formed by ablation on the inner side of the non-woven fabric is repacked by the carbon black coating, rebuilding the electrical connection of the buffer layer, thus effectively repairs the erosion defects of the buffer layer.

In order to obtain polypropylene based cable insulating materials with excellent dielectric properties, polypropylene based composites adding with nano MgO modified by silane coupling agent KH570 was prepared by melt blending method. The effect of nano MgO addition on the microstructure, dielectric properties, and mechanical properties of of the composites was studied. The results show that nano MgO promotes the transformation of polypropylene from α crystallographic orientation β, the interface of polypropylene and nano MgO is well bonded after the nano MgO is modified by KH570. The addition of nano MgO can inhibit charge injection, when the mass fraction of MgO is 1%, the composite has the smallest space charge density, which is 0.6 C/m², while excessive addition of MgO can lead to local charge accumulation in the composites. When the mass fraction of nano MgO is 1%, the composite shows the highest tensile strength (24.6 MPa), while the breaking elongation decreases with the addition of MgO. The direct current breakdown strength of pure polypropylene based material is the lowest. At 100℃, the direct current breakdown strength of polypropylene based composite materials with a MgO mass fraction of 1% is the highest (302 kV/mm), which is only 28.77% lower than that at 20℃.

Epoxy resin (EP) has been widely applied in electrical insulating materials, but with a low thermal conductivity, it cannot meet the requirement of heat dissipation in modern electrical equipment with high-power density. In this paper, silver acetate (AgAc) and 2-ethyl-4-methylimidazole (2E4MI) complex was deposited on boron nitride (BN) surface to prepare imidazole-silver modified BN hybrid materials (Ag(2E4MI)₂Ac@BN), then Ag(2E4MI)₂Ac@BN was filled in EP to prepare Ag(2E4MI)₂Ac@BN/EP composites,and its thermal conductivity was studied. The results show that when the volume fraction of filler is 20%, the thermal conductivity of Ag(2E4MI)₂Ac@BN/EP composites is 1.72 W/(m·K), which is 79.2% higher than that of BN/EP composites (0.96 W/(m·K)). The results of Monte Carlo simulation show that in the EP matrix, the thermal contact resistance (R_c) of Ag(2E4MI)₂Ac@BN is 2.7×10⁶ K/W, which is lower than the that of BN (R_c=5.5×10⁶ K/W). In comparison with BN/EP composites, Ag(2E4MI)₂Ac@BN/EP composites exhibit higher tensile strength and dielectric loss tangent (tanδ), lower dielectric strength and volume resistivity, while maintain good electrical insulating properties.

In order to study the insulating material characteristics of MgO cable and its ampacity evaluation method, in this paper, morphology observation and composition analysis were conducted on MgO powder to determine its purity and inclusions at first. And then the dielectric and thermal characteristic parameters of MgO powder were measured, and the influence of moisture on the dielectric parameters was analyzed. Finally, an equivalent thermal curcuit model for MgO insulated multi-core cables and a simplified analytical algorithm for ampacity were proposed, which was validated by a two-dimensional numerical simulation model. The results show that the volume resistivity of dry MgO samples is higher than 10¹² Ω·m, which can decrease by more than 1 order of magnitude under the effect of moisture. In the frequency range of 10^-1‒10⁴ Hz, the dielectric constant of the dry MgO sample is about 7.9, and the dielectric loss factor is about 5×10^-4‒5×10^-3, which increases significantly after being moisture exposed, especially in the low frequency range. The electric strength of the dry MgO is 3.5‒4.8 kV/mm, and the data measured by different methods have a certain degree of dispersion. The rated ampacity of MgO insulated multi-core cable can be evaluated accurently by using the simplified analytical algorithm, which is beneficial to practical engineering applications.

The surface of basalt fibers was modified by nano alumina, and then modified basalt fiber/epoxy resin composite (BFRP) was prepared by lamination method, and the effect of nano-Al₂O₃ content on the insulation and mechanical properties of the modified composite was experimentally analyzed. The results show that when the mass fraction of nano-Al₂O₃ is 1.0%, the interface modification effect of BFRP is the best. Compared with untreated composites, the dielectric loss factor of 1.0K-BFRP reduces by 38.13%, the surface flashover voltage increases by 42.96%, and the breakdown voltage increases by 33.96%, demonstrating more superior insulation performance; the tensile strength, flexural strength, and interlaminar shear strength increases by 26.46%, 48.19%, and 66.06%, respectively, and the glass transition temperature increases by 4.49℃.

In order to identify the potential risk of enamelled wire quality degradation, the influence of surface conductivity on the electrical insulation performance of enamelled wire was studied, and the electrical breakdown law of enamelled wire was also observed and analyzed. The results show that with the increase of surface conductivity of enamelled wire, the partial discharge (PD) inception voltage decreases significantly. Most of the electrical breakdown does not occur at the bonding position of enamelled wire, but randomly occurs at the weak points of electrical insulation at two adjacent enamelled wire. In the process of production, transportation, and assembly of enameled wire, it is necessary to avoid surface contact with salt substances, and control the environmental humidity during the assembly process， and avoid the surface charge transfer of insulating materials affecting the overall insulation performance of the motor.