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.

Multi-scale mining of the spatio-temporal coupling relationship of dissolved gases in oil is helpful to improve the prediction accuracy of dissolved gases in oil and provide a reliable theoretical basis for transformer operation and maintenance decisions. Thereby, a multi-scale fusion prediction method for dissolved gases in transformer oil considering spatio-temporal coupling information was proposed in this study. Firstly, the Res2Net was used to extract the multi-scale time characteristics of the dissolved gas data in oil, and the periodic time feature information of the characteristic gas under different frequencies was captured. Secondly, the implicit relationship between characteristic gases was captured by calculating mutual information, the correlation between different gases was described in the form of topological graphs, and the spatial information features were extracted by using graph convolutional neural network (GCN). Finally, multi-scale temporal information and spatial information were fused and spliced, and temporal convolution network (TCN) was used to predict the dissolved gas in oil. The proposed method was validated using online oil chromatography monitoring data from a 500 kV transformer. The results show that compared with the traditional prediction method, the Res2Net-GCN-TCN model can effectively improve the prediction accuracy of dissolved gas content in oil, and the average prediction accuracy is 98.68%.

Bushing is an important component of oil-immersed transformers, and its internal insulation moisture, ageing, and development of some defects after long-term operation will cause distortion of local electric field, which seriously threatens the safe operation of bushing. In this paper, the variation patterns of dielectric parameters of the aged and damped oil-immersed paper under different test temperature environment were obtained, and a dynamic dielectric parameter calculation model was established. Meanwhile, a simulation model was established on the basis of actual structure of a 252 kV/1 250 A bushing. Electro-magnetic-thermal coupling multiphysics were used to conduct simulation analysis, and the transient electric field distribution and distortion severity inside the bushing under three typical defect conditions were obtained. The results indicate that when the end screen of bushing is unreliable grounding (resulting in floating potential), electric field distortion occurs at the contact side of bushing and end screen, and the voltage grading effectiveness of capacitive core is weakened. When there is wrinkle on the capacitance screen of bushing, the maximum electric field intensity at the wrinkle regions increases proportionally with the bending curvature. Notably, the field strength inversion phenomena are observed at the distortion zones when the capacitance screen reach specific bending curvature. The bubbles attached on the end screen surface have greater influence on the electric field distribution than bubbles dispersed in transformer oil. Such surface-attached bubbles are prone to produce partial discharge.

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.

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.

Electrical laminated wood is widely used in the field of transformer insulation due to its high mechanical strength, low dielectric loss factor, and dielectric constant close to transformer oil. However, its insulation performance is lower than that of laminated paperboard, and there is a significant risk of insulation accidents when it is used in high field strength area of transformer. In this paper, the raw material selection, processing technology, and current problems of electrical laminated wood were discussed and analyzed, and the influencing factors of its insulation performance were analyzed, providing references for improving the product quality of electrical laminated wood.

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%.

To achieve the healability and reprocessability of silicone rubber insulating materials, it is feasible to introduce healable functional groups into the structural network of silicone rubber to extend its service life and reduce the safety hazards of power system operation. This paper used silane coupling agents to introduce amino groups into the main chain of silicone rubber, and then introduced dynamic hindered urea bonds into the silicone rubber network through the reversible reaction of isocyanates and hindered amines. A healable silicone rubber material was prepared, and the mechanical, electrical, healable, and reprocessable properties of silicone rubber were studied. The results show that the insulation performance of silicone rubber containing dynamically hindered urea bonds meets the application standards. Under certain temperature and pressure, silicone rubber samples can heal mechanical damage and electrical breakdown damage with high healing efficiency. The sample can be reprocessed through the cutting-hot pressing process, and the reprocessed sample can still retain certain mechanical and electrical insulation properties.

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.

A flame retardant monomer 6-(2,5-bis ((4-vinylbenzyl) oxy) phenyl) dibenzo [c,e][1,2] phosphono-6-oxide (DOPVB) was synthesized by using 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxy-10-phosphophenanthrene-10-oxide (DOPO-HQ) and 4-chloromethyl styrene (VBC) as raw materials. The DOPVB flame retardant was compounded with epoxy resin (EP) to prepare EP/DOPVB composites with different phosphorus contents, and their thermal, flame retardant, and dielectric properties were tested. The results show that the optimal synthesis conditions for DOPVB is that the molar ratio of reactants DOPO-HQ, VBC, and K₂CO₃ is 1∶2.2∶3.0, and the reaction time is 6 hours, then the yield is 74.55%. The EP/DOPVB cured material with a phosphorus content of 2.5% has the best comprehensive performance, its glass transition temperature is 130.4℃, which is 45.21% higher than that of pure EP. The dielectric constant is 2.98 and the dielectric loss factor is 0.005 03, which is 21.99% and 72.16% lower than that of pure EP, respectively. The vertical combustion test of the composite material prepared from the cured material reaches V-0 level, with a limit oxygen index of 67.4%.