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 study the effect of coating silicone grease on the distribution of multiple physical fields at the crosslinked polyethylene/silicone rubber composite interface under thermal ageing, the electrical-thermal-mechanical multi-physics field model of 110 kV cable terminal joints was established using COMSOL Multiphysics software. The distribution of electric field, temperature field, and stress field at the composite interface before and after coating silicone under thermal ageing was simulated. The results show that after coating with silicone grease, the sealing degree of the interface increases, which decreases the distortion degree of the electric field and leads to the slight decrease of the temperature rise of the interface, but the stress of the interface distributes unevenly. After ageing, the swelling of silicone grease on silicone rubber increases the relative dielectric constant of silicone rubber, and the interfacial charge density, and causes the electric field strength increase further. The increase of temperature promotes the penetration of silicone grease to silicone rubber, which decreases the thermal conductivity of silicone rubbe and make the interface temperature higher than that before ageing. Under thermal ageing, the elastic modulus of the silicone rubber coating with silicone grease decreases significantly and the interfacial stress decreases further.

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 investigate the application of laser-induced breakdown spectroscopy (LIBS) technology in rapid quantitative detection of insulator contamination, and improve the accuracy and speed of insulator contamination detection, a detection platform based on LIBS technology was established to test artificial and natural contamination samples. The artificial contamination samples were formulated by mixing NaCl, CaSO₄, CaCO₃, and kaolin, while the natural contamination samples were taken from silicone rubber insulators which had been in operation for two and four years in a regional power grid in southern China. The rapid quantitative detection of insulator contamination was carried out by means of the calibration-free LIBS method. The results show that there are 9 kinds of elements with different proportions in the two artificially contaminated samples, while the two naturally contaminated samples contain 9 and 11 distinct elements, respectively. After self-absorption correction, the contaminant elements of the insulators are presented as neatly arranged distribution points on the Boltzmann plot, with consistent regression line slopes, and high fitting degrees, and the spectral line intensities of each element enhances significantly. This effectively mitigates the impact of self-absorption on rapid quantitative detection of insulator contamination, and improves the detection accuracy.

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.

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.

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.

Vegetable insulating oil has gained wide attention due to its green and renewable characteristics as well as excellent fire protection properties, while nanoparticles can effectively improve the electrical properties of vegetable insulating oil. In this paper, the effects of nanoparticles on the electrical properties of vegetable insulating oil were summarized from dielectric loss factor and volume resistivity, and the effects of nanoparticle type, concentration, and surface modification on the breakdown properties of vegetable insulating oil were also discussed. Combining with the differences in the effects of nano-modification on the electrical properties of mineral insulating oil and vegetable insulating oil, we summarized the current research difficulties of nano modified vegetable insulating oil, and prospected the research direction and prospects of nano modified vegetable insulating oil.

Thermosetting epoxy resin is widely used in electrical equipment field due to its excellent thermal conductivity and insulating properties. Due to the stable three-dimensional network structure and insolubility of the thermosetting epoxy resin, its recycling and reuse pose challenges. In this paper, we added different mass fractions of boron nitride (BN) into the epoxy (EP)/4-methylhexahydrophthalic anhydride degradation system to prepare high thermal conductivity, high insulating, and degradable BN/EP composites, and studied their thermal conductivity, dielectric properties, and degradability. The results show that taking 2,4,6-tris(dimethylaminomethyl) phenol as the catalyst, the EP/BN composites can achieve atmospheric pressure degradation at 200℃ under the action of ethylene glycol. The thermal conductivity of BN/EP composite with 15% mass fraction of BN is 0.335 W/(m·K), which is 34% higher than that of pure EP resin; the AC electric strength is 101.7 kV/mm, which is 13% higher than that of pure EP resin. BN/EP composites can be degraded through transesterification to obtain EP degradation products (EDP). After the BN/EP composites are compounded with EDP, the thermal conductivity and electric strength of the BN/EP composites is basically unchanged.

An ANF/BTNF paper-based composite film was prepared taking aramid nanofiber (ANF) as the high-temperature resistant matrix and filling with barium titanate nanofiber (BTNF). The effect of different BTNF content on the dielectric properties of the composite films was studied. The results show that the thickness of ANF/BTNF composite film is about 10 μm. When the mass fraction of BTNF is 0%-20%, both the dielectric constant and electric strength of the composite films increase with the increase of BTNF content. When mass fraction of BTNF increases to 40%, the dielectric constant of the composite film increases significantly, but decreases rapidly at high-frequency zone, and the dielectric loss factor increases significantly, at the same time, the electric strength of the composite film decreases slightly. Therefore, the ANF/20BTNF composite film with 20% mass fraction of BTNF has the best comprehensive dielectric properties, the dielectric constant at 1 kHz reaches 4.78, and the electric strength is 8.90 kV/mm.