Gas chromatography is a common way to determine the dissolved gas content in insulating oils, but there is many types of natural insulating oil, and the Ostwald coefficient is not clear. In order to be able to accurately calculate the dissolved gas content in natural insulating oils, the Ostwald coefficient of seven typical dissolved gases in four natural ester insulating oils was measured using double equilibrium method and compared with the Ostwald coefficient in mineral oil. The results show that there is little difference on Ostwald coefficient of the seven dissolved gases in the three natural esters, while the Ostwald coefficient of dissolved gas in the modified esters is slightly greater than that in the natural esters. The Ostwald coefficient of dissolved gas in FR3 has little relative error compared with the available data, which proves that the data obtained by the method has good credibility.

In this paper, the thermal conductivity mechanism of filled epoxy resins was firstly introduced, and then the research status of the modified epoxy resins doped with different dimensional inorganic thermal conductive fillers was summarized mainly. On the basis of design idea for building the thermal conductive paths, the effect of different dimensions of filler size, distribution orientation, mixed filling, surface functionalization and other factors on improving the thermal conductivity of epoxy resin composites were described emphatically, and a comparative analysis was given. Finally, a brief outlook on the future development of the filled epoxy resin research field was put forward.

In order to improve the heat resistance of the water-soluble silicon steel sheet paint, we prepared water-soluble silicon steel sheets with excellent heat resistance, by adding composite inorganic fillers made of different proportions of precipitated BaSO₄ and inorganic adhesives into water-soluble polyester resin matrix. The mechanical properties, electric strength, and heat resistance of the paint were analyzed. The results show that when the composite inorganic filler disperse in the matrix resin evenly, the pencil hardness reaches to 9H, and the adhesion achieves level 1. With the increase of the proportion of BaSO₄ in the composite inorganic filler, the electrical strength, volume resistivity, and heat resistance increase at first and then decrease. When the mass fraction of BaSO₄ and inorganic adhesive is 5:2, the electrical strength of the paint film reaches a maximum of about 280 kV/mm, and the volume resistivity is as high as 1.5×10¹⁶ Ω·m. The maximum initial thermal decomposition temperature is about 273℃, and the final residual rate is 77%. The performance of the paint is basically unchanged after irradiation, it has stable dimensions and surface resistance after Flinklin burning, it is indicated that the insulating performance is still maintained at high temperature.

In order to compare the properties of domestic and imported meta-aramid paper for traction motor, we tested and analyzed the structure, mechanical properties, and dielectric properties of domestic paper A and B and imported paper. The electrical properties of stator models using the three kinds of paper were tested. The results show that the structure of paper A is relatively loose, and its tensile strength is slightly lower than that of paper B and imported paper; The elongation at break of the three meta-aramid papers is stably maintained at 17%‒19%. The edge tear strength of paper A and B is generally higher than that of imported paper. The breakdown voltage of paper A is slightly lower than that of paper B and imported paper, but the breakdown voltage of paper A is higher than that of paper B and imported paper after impregnation. This is due to the loose structure of paper A, which is conducive to the entry of insulating paint into the paper to fill the gap. The dielectric loss factor, resistance, capacitance, and withstand voltage performance of the stator models are normal, which shows that the two kinds of domestic meta-aramid paper can replace the imported one as slot insulation and filler strip.

The research status and development tendency of semi-alicyclic colorless and transparent polyimide(CPI) film was reviewed from several aspects, including its developing history, important monomers, resins synthesis technology, film production technology, and the practical applications of CPI films in advanced optoelectronic fields. Emphatically, the current hot-topics in the development of semi-alicyclic CPI films were presented, and the future developing trends of semi-alicyclic CPI films were prospected.

In this paper, a photoelectric joint detection system composed of a photomultiplier tube and an electric field sensor was used to carry out the discharge tests of ball-plate electrode gap with burr of different gap distances under positive switching impulse voltage. Compared with the discharge tests of the rod-plate and that of ball plate, the 50% discharge voltage(U_50%) and the physical characteristic parameters under the initial streamer were obtained and compared. The results show that in the ball-plate electrode gap with burr defects, the initial delay, the field strength jump value, and the light power jump value of the initial streamer are positively correlated; in the initial stage of streamer, the burr can shorten the initial delay of discharge, especially for short gap. After the initial streamer developing, the development law of initial streamer of ball-plate electrode with burr is similar to that of rod-plate electrode gap, and the burr aggravates the development of discharge. For the whole discharge process, the burr defect will greatly reduce the discharge voltage of the ball-plate electrode, so that it is close to the discharge voltage of the rod-plate electrode gap under the same clearance.

During the normal operation of converter transformer, moisture will cause the decline of the electrical performance of oil-paper insulation and accelerate its ageing, resulting in a decrease of life and insulation breakdown. In order to study the influence of moisture on the space charge characteristics and breakdown characteristics of oil-paper insulation under AC and DC composite voltage, we prepared oil-paper insulation samples with different water content, then we used space charge measurement under AC and DC composite voltage to get the influence of moisture content on the space charge characteristics of oil-paper insulation under the voltage forms of AC, DC, and AC and DC composite voltage, and studied the breakdown characteristics of samples with different moisture contents under different voltage types. The results show that the electric field distortion rate of oil-paper insulation under AC and DC composite voltage is greater than that under DC and under AC electric field; as the DC component increases, the increase amplitude of breakdown voltage of the samples with higher water content is significantly lower than that of samples with lower water content, and the electric strength of samples with low water content is more affected by the DC voltage component than that of samples with high water content.

In order to master the viscosity, thermal conductivity, electrical conductivity, and dielectric properties of transformer oil with different moisture content from normal temperature to extreme cold, we prepared four samples of 45^# transformer oil with different moisture content, and tested their viscosity, thermal conductivity, electrical conductivity and dielectric properties from +30℃ to -50℃. The results show that with the decrease of temperature, the viscosity of transformer oil increases exponentially, the higher the moisture content, the higher the viscosity of transformer oil. The thermal conductivity is less affected by temperature and moisture content. The electrical conductivity and dielectric loss factor increase at first and then decrease with the decrease of temperature, the higher the moisture content, the higher the peak value of conductivity and dielectric loss factor, and the larger the corresponding peak temperature. While the relative dielectric constant increases approximately linearly with the decrease of temperature, the variation trend of relative dielectric constant of transformer oil with different moisture content is the same and the difference is small.

The electret effect can improve the adsorption capacity of the filter membrane for polar impurities. In this paper, BaTiO₃ doped composite nanofiber filter membrane for transformer insulating oil was prepared by combining electret technology with electrospinning process. The electrospinning conditions for preparing PVDF nanofiber membranes with small diameters and pores without beading were obtained by system study on the relationship between electrospinning parameters and the morphology of fiber membrane. And then the regeneration experiment for transformer insulating oil was carried out. The results show that the filter membrane can remove polar substances, and has high specific surface area and high porosity. After doping BaTiO₃ and corona discharge treatment, the filter membrane can be stably charged. The dielectric loss factor and breakdown voltage of the aged insulating oil are significantly optimized after filtering by the BaTiO₃ doped composite nanofiber filter membrane. Compared with other filter membrane electret-doped composite nanofiber membranes, it has better regeneration effect on transformer insulation oil.

The interface pressure between the cable accessories and the body is the key to the stable operation of the cable. In order to study the influence of long-term cooling and heating cycles on the interface pressure of cable accessories, we designed a test system to simulate the operation state of cable using the temperature control mode of cooling and heating cycles. The dynamic thermo-mechanical analysis of silicone rubber materials before and after the experiment was carried out. The results show that the elastic modulus of silicone rubber material under long-term cooling and heating cycles increases significantly at the test temperature. In addition, with the increase of ageing time and ageing temperature, cable accessories deform irreversibly, resulting in the decrease of interface pressure and the sealing performance. The experimental results are verified by finite element simulation of interface pressure based on cable accessory parameters.