Kelvin probe force microscope (KPFM) is an important tool to measure the surface potential of materials with nanometer resolution. Because of its sensitivity to the surface charge of materials, it has been widely used in the research of dielectric charge behavior in recent years. This paper introduced the principle of KPFM, summarized the latest research progress of KPFM applied to charge behavior in dielectrics, focused on the analysis of the diffusion and migration mechanism of surface and interface charges in dielectrics. And the application of KPFM in typical dielectrics such as inorganic materials, nanocomposites, and ferroelectric materials were also reviewed.

A novel low dielectric loss toughening agent (Si-DABPA) was designed and synthesized, and its structure was characterized, then its toughening effect on bismaleimide (DFE950) was studied. The results show that the Si-DABPA and diallyl bisphenol A (DABPA) have the same reactivity to DFE950. Compared with the DFE950/DABPA cured material, the Thermal degradation resistance of the DFE950/Si-DABPA cured material increases, and the dielectric constant (D_k) and dielectric loss factor (D_f) decrease at 10 GHz. Compared with the DFE950/DABPA/PPE cured material, the tensile strenght of the DFE950/Si-DABPA/PPE cured material increases, while the bending strength and impact strength change little.

To evaluate the environmental adaptability of insulation system for offshore wind turbine, multi-factor cycling tests including high and low temperature test, humid heat test, salt spray test, and vibration test, were conducted on insulating resin and simulation winding, and their electrical performance changes before and after tests were characterized and compared. The result show that after ageing tests, the performance of the epoxy modified unsaturated polyester impregnating resin does not deteriorate significantly, the normal insulating performance of simulation winding just deteriorate slightly, its residual breakdown voltage is almost no attenuation, and both the key materials and simulation winding exhibit good resistance to marine environments. The insulation system of offshore direct-drive wind turbine still retains stable and excellent dielectric performance after long-term offshore multi-factor cyclic ageing tests, which can meet the requirements of marine environment.

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 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.

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.

In this paper, a finite element model of ±400 kV DC wall bushing was firstly established, and the electric field and potential distributions of the DC wall bushing were simulated by COMSOL software. Then the effects of ice edge length, ice cover thickness, and rainfall on the surface electric field of the bushing umbrella skirt were studied. The results show that when the ice edge length increases to bridge the umbrella skirt, the electric field distorts seriously. The increase of ice thickness has little influence on the maximum surface electric field of the umbrella skirt. When the rainfall reaches 10 mm, the maximum surface electric field of the umbrella skirt increases sharply, and the electric field distortion points increase. The research results can provide reference for the development and design of UHV and EHV DC wall bushing.

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.

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.