Under the high temperature conditions (90, 105, 120, and 135°C), accelerated ageing tests of nitrile rubber (NBR) were conducted in hot air, hot oil, hot air compression, and hot oil compression. The ageing mechanisms were investigated through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA/DTG), and scanning electron microscopy (SEM), and the effects of ageing temperature, time, and deformation conditions on the ageing behavior of NBR were revealed. The results indicate that crosslinking, oxidation, and chain-breaking reactions occur during the ageing process of NBR, and the crosslinking reaction is the predominant reaction. After ageing at 120°C, grooves appear on the surface of NBR, and after ageing at 135°C, defects such as holes and damages appear on the surface. In the early stage of ageing, transformer oil has a suppressive effect on the increase of permanent deformation under compression. In the later stage of ageing, transformer oil plays a promote role for the decrease of tensile strength, and the higher the temperature, the more obvious the effect.

In order to realize the synergistic enhancement of electrical-mechanical properties of epoxy resin for power electronics encapsulation, CaCO₃ oligomer inorganic nanoparticle filler was prepared by solution method, epoxy resin was carried out organic matrix-inorganic filler modification together with organic silicone, and single inorganic modified, single organic modified, and organo-inorganic jointly modified epoxy resin composites were prepared. Taking the pure epoxy resin as a reference, the AC electric strength, DC volume conductivity, surface potential attenuation characteristics of the four epoxy resin composites were investigated, and the internal trap energy levels were calculated from them, while their bending strength and impact strength characteristics were also investigated. The results show that the electrical properties of single inorganic modified, single organic modified, and organic-inorganic co-modified epoxy resin composites are significantly improved, and their electric strength increases by 6.55%, 12.66% and 9.61%, respectively. Their DC volume resistivity is 5 times bigger than that of pure epoxy resin, the surface potential decay rate decreases, the trap density and trap energy increase, but the improvement of electrical properties by the organic-inorganic co-modification do not superimpose compared with single modification. The flexural and impact strengths of the modified epoxy resin composites significantly increase, with exponential growth compared to the pure epoxy resin. The research results provide a reference for the performance improvement of modified epoxy resin composites in the field of power electronics insulation and encapsulation.

The stator winding insulation of 10 kV three-phase asynchronous motor will subject to thermal, electrical, environmental, and mechanical stresses during operation, which will generate insulation defects and lead to partial discharge (PD). It is very difficult to obtain the reference voltage waveform in on-line monitoring condition, and the loss of reference phase makes it impossible to use PRPD pattern in PD recognition. To solve these problems, three kinds of PD models, e.g. internal discharge, slot discharge, and corona discharge, were made in the laboratory conditions, and the PD signals were collected. The polar coordinate method was used to convert PRPD pattern into circular polar coordinate pattern to solve the problem of reference phase loss. The results indicate that different types of PDs have different polar coordinate pattern characteristic distributions, the internal discharge has symmetrical distribution in the first and third quadrants. Slot discharge and corona discharge have unsymmetrical distribution, and the amplitude of the third quadrant is much larger than that of the first quadrant. The slot discharge has larger point cluster discharge concentration range and wider discharge shape than corona discharge. The characteristic parameters such as skewness, kurtosis, and discharge proportion are obviously different in different discharge types. With the increase of voltage level, the distribution and characteristic parameters of polar coordinate pattern will change obviously.

To solve the problem that it is difficult to diagnose the moisture defects of cable joints with the existing methods, this paper proposes a method for diagnosing the moisture defects of cable joints based on frequency modulated continuous wave (FMCW) and time reversal (TR). Firstly, a distributed parameter model of cable was established. The FMCW method was employed to capture multi-frequency reflected signals from impedance mismatches at defects and joints. These inversion signals were injected into a test cable model to derive an energy curve, and the energy curve is served as a diagnostic spectrum for cable defects. Subsequently, the impedance discontinuity point detection was carried out for the simulation cable models with different end-loads and intermediate joints. Finally, joint defect diagnosis was carried out for the real 750 m 10 kV power cable and 2 km 10 kV power cable. The results show that the method proposed in this paper can not only accurately determine the location and characteristic of the impedance discontinuity points in cable, but also improve the distance resolution of the defect location peak. The joint positioning peaks of "positive first and then negative" and "negative first and then positive" can respectively represent normal and damp cable joints. Therefore, the method proposed in this paper can accurately detect the moisture defects of cable joints and has a good engineering application prospect.

There are many types of insulating oils and insulating papers with different compositions, which will have different moisture equilibrium curves when they are used in conjunction. To obtain the moisture equilibrium curves of different oil-paper insulation systems, this research constructed a moisture equilibrium curve model applicable to new oil-paper insulation systems based on the relative moisture content relationship between oil and paper at moisture equilibrium, and verified the model by combining with the measured results of moisture equilibrium experiments. The results show that under typical operating temperature of transformer, the prediction accuracy of the moisture equilibrium curve model for different oil-paper insulation systems is higher than 90%, confirming the effectiveness of the model.

The disadvantages of poor thermal conductivity and mechanical properties severely restrict the further application of epoxy resin in electrical equipment insulation. Therefore, Epoxy composite dielectrics (EP/BNNS) with different BNNS contents were prepared by using nitride nanosheets (BNNS) as fillers. The phonon transport, stress distribution, polarization relaxation, trap distribution, and other conditions inside the epoxy composites dielectric were analyzed, and then the mechanisms of BNNS improving the thermal, mechanical, and electrical properties of the epoxy composite dielectric were systematically explored. The results show that when the BNNS filling mass fraction is 5.0%, the thermal conductivity of the epoxy composite dielectric reaches 0.36 W/(m·K), the bending strength and tensile strength reach 120 MPa and 57.4 MPa, respectively, and the electric strength reaches 96.9 kV/mm, while the composites dielectric also have good dielectric properties. The introduction of BNNS can optimize the thermal and mechanical properties of the epoxy composite dielectric without compromising their electrical performance.

Basin insulators in GIS are prone to surface electric field distortion due to charge accumulation, which can lead to surface flashover. To improve the surface voltage resistance performance of insulators, this paper refers to the design concept of surface functional gradient materials and utilizes the uniform treatment characteristics of titanium deposition by atmospheric pressure plasma jet (APPJ). By controlling the treatment time at different radial distances, a basin insulator with continuous conductivity gradient were prepared. At the same time, a fast electric field calculation method based on surface conductivity was established by coupling DC electric field simulation calculations with an attention mechanism-enhanced long short-term memory network (LSTM). The surface conductivity of the basin insulator was continuously gradient optimized using the artificial bee colony (ABC) algorithm. And the electrical performance of the insulator before and after optimization was evaluated and compared using simulation models and flashover tests. The result show that the density and bonding structure of the plasma titanium deposition layer are related to the treatment time, and the optimal treatment time is 3 minutes, at which the surface conductivity of the insulator is the highest. The surface functional gradient modification significantly improves the uniformity of the electric field distribution on the insulator surface. The maximum field strength on the lower surface of the insulator decreases by 70.3%, the electric field distortion rate decreases by 24.69%, and the flashover voltage is 31.34 kV, which is 14.3% higher than that of unmodified insulators.

The heat resistance of ethylene propylene diene monomer (EPDM) decreases significantly after thermo-oxidative ageing, resulting in poorer performance and shorter service life of products made from it. This paper reviews the research progress on improving the thermo-oxidative ageing resistance of EPDM at home and abroad. It introduces three main methods for improving the thermo-oxidative ageing resistance of EPDM, including selecting high thermal-resistant EPDM matrix, compounding with thermal-resistant rubber, and adding antioxidants. And it provides a brief outlook on future research directions for improving the thermo-oxidative ageing resistance of EPDM.

The crystallinity of chopped fibers has an important impact on the mechanical strength, thermal shrinkage resistance, toughness, and other properties of aramid paper. To investigate the influence and mechanism of chopped fibers crystallinity on the properties of meta-aramid paper, meta-aramid papers with different crystallinity of chopped fibers were prepared by controlled variable method, and their mechanical properties, electrical properties, and thermodynamic properties were tested. The results show that the electric strength of meta-aramid papers is not significantly affected by the crystallinity of chopped fibers, it is mainly determined by precipitated fibers. The tensile index of meta-aramid papers is almost not affected by the crystallinity of chopped fibers before hot-pressing, but increases with the increase of the crystallinity of chopped fibers after hot-pressing. When the crystallinity of chopped fibers increases from 27.19% to 47.91%, the tensile index of papers enhances from 46.2 N·m/g to 58.0 N·m/g. In addition, the thermal shrinkage resistance of papers is closely related to the crystallinity of chopped fibers. When the crystallinity of chopped fibers increases from 27.19% to 47.91%, the thermal shrinkage rate of papers decreases from 4.8% to 1.3%.

The vacuum surface insulation performance of insulation material used in radiation environment simulation devices will be significantly affected by long-term radiation exposure. By conducting irradiation ageing experiments of different doses of gamma ray on polymethyl methacrylate (PMMA) materials, the variation law of surface microstructure and electrical performance parameters of PMMA materials with gamma ray irradiation dose was studied. The results show that when irradiated under a low-dose (0.1 kGy) gamma rays, the distribution of surface traps on the material is the main factor affecting the vacuum surface withstand voltage characteristics of PMMA the vacuum surface ageing voltage of PMMA increases by 11.7% compared to the unirradiated sample. When irradiated with high doses (greater than 1.0 kGy) of gamma rays, holes appear on the surface of PMMA material, and the local electric field intensity is distorted, becoming a "weak area" of vacuum surface insulation. Appropriate doses of gamma ray irradiation is helpful to improve the vacuum surface insulation performance of PMMA.