In this research, cyanate ester-bismaleimide-hydrocarbon (BT-CH) composite resin system and BT-CH copper clad laminates (CCL) were prepared by introducing hydrocarbon (CH) resin into ester-bismaleimide (BT) resin system. The curing kinetic parameters of BT-CH composite resin system were studied by differential scanning calorimetry (DSC), Fourier infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The dielectric loss (D_f) and thermal oxygen ageing properties of BT-CH composite resin were investigated after curing. The results show that the reaction order, activation energy, and frequency factors of BT-CH composite resin system are smaller than those of BT system, CH can promote the curing reaction of BT. According to the FTIR spectra of BT-CH CCL, the characteristic peaks of cyanate group, imide group, and vinyl group disappear or weaken, while that of triazine ring appear, the reaction of resin system is sufficient. SEM shows there is no hole or other microdefect in the BT-CH substrates. The D_f of BT-CH substrate is 25% higher than that of BT substrate, and the D_f of BT-CH substrate increases by 6% after thermal oxygen ageing at 153℃ for 4 weeks, which has excellent thermal oxygen ageing resistance.

Organic-inorganic composite dielectrics are often difficult to have both high dielectric constant and high electric strength. In this paper, a sandwich structured composite film was prepared by using aramid nanofibers (ANF) as high-temperature resistant matrix, boron nitride nanosheets (BNNS) as electrical breakdown enhancer, and barium titanate particles (BT) as dielectric modifier through step-by-step vacuum filtration and hot-pressing method, and the effects of sandwich structure and different modifier content on the microstructure and dielectric properties of the composite films were studied. The results show that the sandwich structured composite films have high flexibility and excellent high-temperature stability. The addition of BT decreases the electric strength of single layer and sandwich structured composite films, while the addition of BNNS increases the electric strength of the composite films. The individual addition of BT or BNNS can increase the dielectric constant of composite films at low frequency, while the simultaneous addition of BT and BNNS can increase the dielectric constant in wide frequency domain. Therefore, a composite film with balanced dielectric properties and electric strength can be obtained by adjusting the sandwich structure and modifier content in each layer. When taking the ANF/BNNS film with 10% mass fraction of BNNS as the outer layer and the ANF/BT film with 10% mass fraction of BT as the core layer, the dielectric constant, dielectric loss factor, and electric strength of the prepared composite film is 1.41 (1 kHz), 0.013 (1 kHz), and 13.3 kV/mm, respectively.

In order to improve the bonding strength of epoxy resin potting materials to metals, the effects of molecular structure, amine curing agent type, and inorganic fillers on the tensile shear strength of epoxy resin potting materials were studied. The results show that the epoxy materials prepared by polyurethane modified epoxy resin and dimer-acid modified epoxy resin have higher tensile shear strength. The tensile shear strength of epoxy materials cured by polyamide, polyether amine, and aromatic amine decrease in turn. With the increase of inorganic filler content, the tensile shear strength of epoxy materials increases at first and then decreases. For the nano gas-phase SiO₂ powder, when its filling mass fraction is 4%, the epoxy material has higher adhesive strength, while for the micro powder, its filling mass fraction needs to reach 40%, the epoxy material can have higher adhesive strength.

The technical standards of insulating oil at home and abroad were summarized and the technical requirements of insulating oil for high voltage instrument transformer were pointed out. The using properties of five kinds of insulating oils commonly used in high voltage instrument transformer in China were compared and analyzed. The results show that No.1 and No.2 insulating oils are negative gassing insulating oil, which are suitable for high voltage instrument transformers. No.3, No.4, and No.5 insulating oils are positive gassing insulating oil, which are not suitable for high voltage instrument transformers. On the balance of aromatics content, gassing properties, gas production properties, sludge solubility, and oxidation stability, No.1 insulating oil has the best comprehensive performance, the lowest gassing, and the best oxidation stability.

In order to investigate the effect of alkaline corrosion on the insulating strength of superhydrophobic coatings, superhydrophobic coating specimens with insulating properties were prepared and subjected to artificial alkaline corrosion tests. The insulating strength of the superhydrophobic coating specimens with different corrosion degrees was tested, and the effects of pollution degree, applied voltage amplitude, and wetting degree of surface contaminants on their insulating strength under different temperatures were investigated. The results show that the alkaline environment will destroy the substance and structure of superhydrophobic coating surface, leading to the decrease of its hydrophobicity and self-cleaning capability, which in turn leads to the decrease of its insulating strength. The more serious the surface pollution degree of the alkaline-corroded superhydrophobic coating under wet and polluting environment, the higher the applied voltage, and the shorter the wetting time, the lower the insulating strength of the coating surface. The surface pollution degree of the alkaline-corroded superhydrophobic coatings gradually decreases to a stable value with the increase of wetting time, at this time the surface leakage current of the coating does not change significantly, and the lower the temperature of alkaline corrosion environment, the shorter the wetting time required to reach the above stable state.

The existing test method standards of the compatibility between electrical insulating fluids and structural materials at home and abroad were introduced, and the test method standards of the compatibility between electrical insulating fluids and structural materials in transformers, power capacitors, cable terminals, and oil cooling motors were discussed respectively. The similarities and differences of test conditions and evaluation parameters in each standard were summarized, and the shortcomings of current standards were analyzed. At last, the standard proposal of IEC 63177 Test methods for compatibility of construction materials with electrical insulating liquids proposed by Guangzhou Power Supply Bureau of Guangdong Power Grid Co., Ltd. was introduced compendiously, which will address the shortcomings of existing compatibility test methods.

In order to improve the strength of composite foam material used for post composite insulator core, the poly(p-phenylene benzobisoxazole) (PBO) fiber was used to reinforce composite foam material, and the fiber content suitable for internal insulation applications was determined by studying the effects of different content of PBO fiber on the thermal, mechanical, and insulating properties of composite foam material. The results show that the addition of PBO fiber endows the composite foam materials with the ability to resist impact damage. When the mass fraction of PBO fiber is 0.4%, the energy absorbed by the composite foam materials in the drop weight impact test reaches the maximum. The addition of PBO fiber can decrease the thermal expansion rate of the material, improve the thermal stability, reduce the potential thermal stress risk, and has little effect on the internal insulation performance of composite foam materials.

An accelerated thermal ageing test was designed for the main insulation sample of a generator VPI stator bar, and the ultrasonic velocity, ultrasonic spectrum, and ultrasonic defect waveform of samples were analyzed at various ageing temperatures on the basis of the principle of ultrasonic testing. At the same time, artificial hole defects and impurity defects were introduced into the insulation samples to explore the effect of defect introduction on the ultrasonic waveform of the samples. The results show that as the thermal ageing test progresses, the overall ultrasonic velocity in the main insulation of stator bar shows a decreasing trend. The reason is that during the thermal ageing process of the stator bar main insulation sample, the layering of internal structure can cause refraction, reflection, and dissipation of the sound wave during propagation process, resulting in the propagation speed of the sound wave in the insulation sample decrease. The defects can be detected and accurately located through ultrasonic echoes, which indicates that the acoustic performance testing method has good practicality in the diagnosis of stator bar main insulation.

After the ageing of sealant, the moisture will invade the crimping interface from the sealant interface, leading to insulator ageing. To investigate the affecting mechanism of various ageing factors on the interface samples between sealant and armour clamp, immersion tests were conducted on the sealant samples in deionized water, salt solution, nitric acid solution, sulfuric acid solution at room temperature for 28 days, as well as immersion tests in mixed solutions of sulfuric acid or nitric acid with salt at different temperatures. Then the ageing situation of the samples was analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The results show that the sulfuric acid solution has no significant effect on the siloxane matrix of sealant, while the salt solution can cause the breakage of methyl chain of the siloxane side chain, and the nitric acid solution can oxidize the siloxane side chain to generate -OH. The influence of nitric acid and salt mixed solution on the siloxane matrix at room temperature is greater than that at high temperature, and the effect of nitric acid and salt mixed solution on the siloxane matrix is basically equivalent to the superposition of the two solutions acting separately. The influence of sulfuric acid and salt mixed solution on the sealant at high temperature is greater than that at room temperature. The main affecting mechanism of sulfuric acid and salt mixed solution on the siloxane matrix is that the salt solution causes the methyl of silicone side chain to break, making the Si-O-Si main chain expose to sulfuric acid and undergo chain breaking, then the salt solution can continue to affect the deeper methyl groups.

Free metal particles are usually regarded as one of the most hazardous contaminants in the liquid-phase insulation of converter transformers, which can lead to the partial discharge (PD) initial voltage and breakdown voltage of equipment decrease obviously. In this paper, a transformer oil circulation system was constructed, and DC partial discharge and breakdown experiments were conducted on the transformer oil containing metal particles at different oil flow velocity. The PD characteristic parameters were extracted, and the variation of characteristic breakdown voltage with oil flow velocity was obtained. Then the affecting mechanisms of oil flow velocity on the PD and breakdown characteristics were discussed combined with the particle distribution images between electrodes. The results show that when the oil is static, the partial discharge degree of the transformer oil containing metal particles is highest. With the increase of oil flow velocity, the PD initial voltage increases, and the discharge repetition rate and the accumulation discharge magnitude per unit time decrease. When the oil is static, the breakdown voltage of the transformer oil containing metal particles is lowest. With the increase of oil flow velocity, the Weibull distribution curve of breakdown voltage shifts to the right, and the characteristic breakdown voltage increases, that is, the flowing of oil improves the insulating properties of transformer oil and reduces the breakdown possibility remarkably.