A MWCNTs/T-ZnOw/PVB composite was prepared via solution blending method by using multi-walled carbon nanotubes (MWCNTs) and zinc oxide whisker (T-ZnOw) as fillers and polyvinyl butyral (PVB) as matrix. The thermal diffusivity of the composite was measured by transient electro-thermal technique (TET). The effects of different mass fraction ratio of fillers, heat treatment time and temperature, and ultraviolet accelerated ageing on the thermal conductivity of the composite were investigated. The results show that under the same mass fraction of fillers, the thermal conductivity of the composite increases at first and then decreases with the increase of MWCNTs content. When the heat treatment time is 1 h, with the increase of the heat treatment temperature from 80℃ to 140℃, the thermal conductivity of the composite decreases at first and then increases. When the heat treatment temperature is 140℃, the thermal conductivity increases after heating for 1 h, but it decreases with the extension of heating time. When the composite is accelerated aged by ultraviolet irradiation, the thermal conductivity of the composite decreases with the increase of irradiation time.

The effects of thermal conductive fillers on the tensile strength and thermal conductivity of EPDM composites were studied by filling EPDM rubber with multi-scale alumina, nano-zinc oxide alone, and their mixer. An EPDM thermal conductive composite with good mechanical properties was prepared, and its insulating properties were tested. The results show that when the addition amounts of multi-scale alumina and nano zinc oxide are 200 phr, respectively, the thermal conductivity of the composites is 1.12 W/(m·K), the tensile strength is 5.01 MPa, and the tear strength is 21.12 N/mm.

In order to improve the dielectric properties, insulating properties, and thermal conductivity of polymer composites comprehensively, on the basis of boron nitride nanoplates (BNNS) modified polyvinylidene fluoride hexafluoropropylene(P(VDF-HFP)), we prepared a three-layer (P(VDF-HFP)/P(VDF-HFP)-BNNS/P(VDF-HFP)) composite by layer by layer solution casting method, the bottom and top layer were the P(VDF-HFP) film, and the middle layer was the modified P(VDF-HFP) film with 0, 1%, 3%, 5% volume fraction of BNNS, respectively. The properties of the composites were analyzed. The results show that compared with the pure P(VDF-HFP) and the single layer composite films modified with 1% BNNS, the dielectric properties of the three-layer polymer material modified with 1% BNNS is improved obviously, its dielectric constant and dielectric loss factor is 8.52 and 0.022 at 1 000 Hz, respectively. Its electrical breakdown property and thermal conductivity are more excellent, the electric strength is 452.6 MV/m, which is 17.3% and 24.9% higher than that of the pure P(VDF-HFP) and the single layer composite films modified with 1% BNNS, respectively, and its thermal diffusion rate is 0.04 mm²/s, which is 25% and 5.3% higher than that of the pure P(VDF-HFP) and the single layer composite films modified with 1% BNNS, respectively.

The composite insulation cross arm has the characteristics of light weight and high strength, which can play an important role in reducing the area of the line corridor and strengthening the insulation capacity of the power grid. The electrical insulation performance of the internal insulation interface is related to the safe and stable operation of the power system. In this study, based on IEC 62217:2012, a 144-hour water diffusion test was carried out on the interface specimens of the inner-filled composite crossarm, and the leakage current and breakdown at different stages were measured. Combined with the test results, the insulation crossarm samples were analyzed. Interface ageing characteristics under water diffusion test conditions. The results show that when the water diffusion time is 144 h, the leakage current of the sample is as high as 20 mA, which is 1000 times that of the sample without the water diffusion test, and the interface breakdown time is faster than that of the sample without the water diffusion test. 65%, water molecules have a destructive effect on the interface under the action of high temperature diffusion, and the longer the water diffusion time, the greater the damage to the polyurethane/glass fiber reinforced plastic interface.

The space charge accumulation and dissipation characteristics of the oil-paper insulation systems composed of different types of transformer oils were studied under the conditions of applying and removing different intensity of DC electric field. The results show that compared with paraffin-based transformer oil, the naphthenic transformer oils have higher naphthenic hydrocarbon content, more suitable aromatic hydrocarbon content, and higher charge transfer rate, and the oil-paper insulation systems composed by them has less charge accumulation and the charges dissipates more easily after applying and removing the high voltage DC electric field, which is beneficial to the dissipation of charge in oil-paper insulation for converter transformer.

In order to study the effect of nano Al₂O₃ on the DC electrical tree of epoxy resin, epoxy and epoxy/Al₂O₃ nanocomposites were prepared. The samples were conducted electrical tree test and partial discharge detection by using needle-plane electrode, and the inception, growth, and ageing of DC electrical tree and corresponding partial discharge characteristics were analyzed. The results show that the addition of nano-Al₂O₃ particles can decrease the initiation probability and growth rate of DC electrical tree in epoxy resin. When the mass fraction of Al₂O₃ is less than 3%, the higher the content of Al₂O₃, the stronger the ability to suppress the electrical tree. In addition, the faster the voltage rise rate, the higher the initiation probability of DC tree in epoxy resin. When the voltage applying time is about 1 800 s, the DC electrical tree stops growing, and the electrical trees are all branch trees. Partial discharge is an important reason for DC electrical tree ageing of epoxy resin, and the partial discharge pulse clusters appear in the voltage rise and fall phases in each cycle mainly, which is due to that the electrical trees grow faster at these two phases. By comparing the partial discharge test results of pure epoxy resin and the nanocomposites with 1% Al₂O₃, it is found that nano-Al₂O₃ can suppress the partial discharge in the electrical tree developing process, which leads to the decrease of discharge pulse amplitude and appearing of more sparse partial discharge areas, indicating that the nano particles can suppress the development of electrical tree by suppressing partial discharge.

The most important component of high thermal conductivity main insulation material for large generators is high thermal conductive epoxy adhesive. As an important component of high thermal conductive epoxy adhesive, BN powder can improve the thermal conductivity of epoxy resin, but it would affect other properties. In this paper, the researches of high thermal conductivity main insulation materials were analyzed and summarized. It was found that BN powder can inhibit the generation and aggregation of space charge in BN/epoxy composites effectively, and reduce the threshold electric field of space charge in BN/epoxy composites. The addition of BN powder could reduce the electric strength of BN/epoxy composites, under the same BN mass fraction, the electric strength of micron BN/epoxy composites was lower, and the conductivity of the composites could be reduced more effectively by nano BN than by micro BN. The surface flashover voltage of the composite decreased after charging on its surface. Then the research direction of high thermal conductivity adhesives in the main insulation materials for large generators in China was proposed.

According to the structure characteristics of HX_D1 locomotive high voltage wall bushing, the electric fields of an imported high voltage wall bushing and the domestic high voltage wall bushing were analyzed by COMSOL finite element method. Then a domestic high voltage wall bushing was produced by the automatic pressure gel (APG) forming technology combining with the application situation of the imported high voltage wall bushing, its electrical properties were compared, and environmental tolerance tests of thermal-cold oil cycling, vibration impact, and high and low temperature alternating were conducted. The results show that the domestic high voltage wall bushing has reasonable structure and good environmental adaptability, which is suitable for the traction transformer field of HX_D1 locomotive.

With the development of advanced electronics and high frequency communication technology, polyimide (PI) film faces more and more high thermal conductivity requirements as an important polymer insulating material. The intrinsic thermal conductivity of traditional PI film is smaller, which cannot meet the rapid cooling requirement of electronic components. In recent years, researchers had carried out a lot of researches on thermally conductive PI films and a series of polyimide-based composite films were prepared by adding inorganic thermally conductive fillers. In this paper, we summarized the latest research progress in thermally conductive PI-based insulating films and discussed the relevant thermal conduction behavior. The key factors influencing the thermal conductivity of films, which include fillers types, particle sizes, addition amount, and the interface interaction between fillers and polyimide matrix, were described systematically. In addition, the technical challenges of high performance polyimide-based thermally conductive insulating film materials were summarized and proposed.

The conventional properties, viscosity characteristics, gel characteristics, storage stability of YD319G3 epoxy modified unsaturated polyester impregnating varnish and its application in the partial model product of direct drive permanent magnet synchronous wind turbine generator were studied. The results show that the YD319G3 impregnating varnish has low toxicity and low volatility characteristics, which can meet the requirements of VPI insulation treatment process for large wind turbines, and the impregnated model and product have good insulating properties. It is a suitable impregnating resin for the VPI treatment of wind turbines.