Taking urea and hexagonal boron nitride as raw materials, we prepared an amino modified boron nitride nanosheets (BNNS) by ball milling method, and then prepared a BNNS/epoxy composite by mixing the BNNS before and after modification with epoxy resin. The effect of amino modified BNNS on the surface insulating properties of epoxy resin was studied. The results show that the amino group is grafted on the surface of BNNS successfully by ball milling method, which improves the dispersion of fillers in epoxy composites. When the mass fraction of the modified BNNS is 0.5%, the flashover voltage of the BNNS/epoxy composite increases by 26.9% compared with the pure epoxy resin. In addition, the amino modification reduces the trap energy level on material surface and accelerates the space charge dissipation rate. The dielectric constant and dielectric loss factor of the composites filled with amino modified BNNS increase slightly. The flashover voltage of the composites can be improved by balancing the effects of space charge dissipation and polarization relaxation.

On the basis of radiation spectral characteristics of insulation abnormal discharges, a dual-spectral discharge detection method was proposed. The differences of spectral distribution characteristics under corona discharge, spark discharge, and arc discharge were obtained through experiments, and a dual-spectral sensor based on solid avalanche array was developed. The evolutional relationship between the dual-spectral characteristics and discharge energy was studied using this sensor, and then the discharge hazard quantification criteria based on dual-spectral intensity ratio was summarized. The results show that the light radiation under three kinds of discharge modes has a certain polarity effect. There is a strong correlation between the dual-spectral intensity ratio and the discharge intensity, and there is almost no intersection for the variation range of dual-spectral ratio of low-energy discharge and high-energy discharge, which can be used as an effective criterion to judge partial discharge or arc discharge, and provide a new approach for the optical monitoring and diagnosis of abnormal discharges in equipment.

Three kinds of solvent-free vacuum pressure impregnated (VPI) insulating varnishes for wind turbine generator were introduced, and their chemical composition and properties were compared with those of the current solvent-containing insulating varnishes. The results show that the solvent-free insulating varnishes have the advantages of low volatilization, environmental protection, and good process applicability, which can meet the technical requirements of current insulating varnish.

Dodecylbenzene (DDB) is a kind of weak polar dielectric material widely used in self-contained high voltage oil filling cable and its accessories. A domestic dodecylbenzene insulating oil was selected as research object, and its physical and chemical properties, and electrical properties were tested. A test system for simulating different types of electrical faults in oil was established, and the gas production characteristics of the dodecylbenzene under two electrical faults of power frequency breakdown in oil and flashover along the oil-paper surface were studied. The results show that the dodecylbenzene insulating oil has excellent physical and chemical properties, and electrical properties. H₂ and C₂H₂ are the characteristic gases under two electrical faults. According to the dissolved gases analysis (DGA) technology of mineral oil, the three ratio method of IEC is suitable for the fault type diagnosis of dodecylbenzene insulating oil, while the Dewey triangle method is not suitable.

An epoxy insulating material with high moisture resistance was prepared by grafting the hydroxyl terminated polydimethylsiloxane on o-cresol epoxy resin, and its properties were analyzed from the perspective of theoretical calculation and experiment. The results show that when the mass fraction of hydroxyl terminated polydimethylsiloxane is 10%, the modulus and toughness of the modified epoxy resin are higher, the volume change rate at high temperature is smaller. In the layer model of modified epoxy resin and water, the water molecules diffuse away from the epoxy resin. The water absorption of modified epoxy resin is decreased by 13.74% compared with the unmodified epoxy resin. After water absorption, both the volume resistivity and surface resistivity of the modified epoxy resin sample are higher than those of the unmodified epoxy resin, and its electric strength increases by 1.1 kV/mm compared with the unmodified epoxy resin.

Firstly, a natural ester was exposed to the air, and the relationships between its properties and exposure to air duration were measured. Then the oxidation situation of insulating part impregnated with natural ester in air was observed, and the natural ester on the insulating part was removed by traditional gas-phase drying method. Finally, the withstand field strength of solid insulating parts in natural ester transformer was calculated by an electric field analysis software. The results show that the water content of the natural ester increases significantly after exposure to air, but its other characteristics change little. There is no oxide film forming on the surface of insulating parts after exposed to room temperature for two months. The natural ester in insulating parts cannot be removed by gas-phase drying method completely. The withstand field strength of insulating parts in natural ester transformer is 10% higher than that in mineral oil transformer with the same structure.

A nano organic silicone oxide sol was prepared by the hydrolysis and polymerization of methyl triethoxysilane and tetraethyl orthosilicate, which was converted into SiO₂ equivalent to mixed with polyamide-imide (PAI) resin through high-speed shearing, and then organic silicone oxide hybrid PAI composite films were prepared through film spreading and thermal curing. The composite films were characterized by infrared spectroscopy, X-ray diffraction, and SEM, and their dielectric spectra, electric strength, and corona resistance lifetime at high temperature (155℃) were tested. The results show that the nano organic silicone oxides disperse uniformly in an amorphous state in the resin matrix. With the increase of the nano organic silicone oxide content, the dielectric constant and dielectric loss factor of the hybrid PAI composite films increase gradually, the electric strength decreases gradually, and the corona resistance life increases at first and then decreases. When the mass fraction of the nano organic silicon oxide is 15% of SiO₂ equivalent, the corona resistance life of the hybrid PAI composite film at high temperature is 3.1 times longer than that of pure PAI film.

Mechanical impact is an important factor that damages the stator bar insulation material. At present, systematic researches on the damage of stator bar insulation materials by mechanical impact are still lack. In this paper, the effect of mechanical impact on the stator bar insulation material was studied by combining the finite element simulation and experiment. The results show that when the insulating material is subject to mechanical impact, the average equivalent stress-strain and electric strength firstly increase or decrease, and then become stable within a certain impact strength range under the same punch structure. Under the same impact strength, both the average equivalent stress-strain and electric strength increase with the increase of the tip area of punch head. The correlation between the average equivalent stress-strain and the electric strength can be used to evaluate the insulation damage of stator bar caused by mechanical impact.

XLPE cable insulation is prone to age under the long-term influence of electrical stress. In order to study the electrical ageing characteristics of XLPE cable, we conducted accelerated electrical ageing experiments on 10 kV XLPE cable, and the physic-chemical properties and electrical properties of the XLPE cable before and after ageing were investigated. The results show that the crystallinity of XLPE decreases significantly after electrical ageing, and the melting peak characteristic temperature of XLPE decreases slightly. The methylene content of XLPE increases, and carbon-carbon double bonds start to appear inside the material. PDC test results show that the polarization and depolarization current of the samples increase after electrical ageing, and the conductivity and low frequency dielectric loss of XLPE increase significantly. This is because the chemical bond break in XLPE molecular chain is broke by high-energy electron bombardment, resulting in the increase of short-chain molecules number and degradation of crystalline region, which ultimately decrease the physic-chemical and electrical properties of XLPE insulation material.

Compared with mineral oil transformer, vegetable oil transformer has the characteristics of strong overload capacity, high fire safety, and good environmental performance. At the same time, its noise generated during operation is smaller than that of dry-type transformer, and the loss is lower, the size is smaller, the price is lower. So more and more power grid and industrial users began to use vegetable oil transformer. The current research progress of vegetable oil transformer from the aspects of design, material application and research, production and operation maintenance was summarized in this paper, and the research direction and prospect of vegetable oil transformer were prospected.