Under the effect of high temperature, the oil-immersed paper in operating transformer ages gradually, and its resistivity changes with ageing. To get a more complete understanding of the various factors except water that affect the resistivity of oil-immersed paper during the ageing process, at first, we conducted accelerated thermal ageing on the paperboards in vaccum to prepare samples with different degrees of polymerization (DP). Then the water content in the samples was controlled strictly, and their resistivity was measured in vacuum to explore the influence of DP on their resistivity. After that, the paperboards with different DP were immersed in mineral oil with different resistivity to explore the influence of the resistivity of oil on that of oil-immersed paperboard. Finally, the oil-immersed paperboards were accelerated aged, and the change of their resistivity after ageing was observed. The test results show that the resistivity of paperboard slightly increases after ageing, and the increasing trend is partially offset after inmmersing in oil, but there is no significant effect law of oil with different resistivity on resistivity of oil-immersed paperboard. When the water content is simmilar, the resistivity of oil-immersed paperboard decreases significantly with the increase of ageing products. It is concluded the decrease in resistivity of oil-immersed paperboard during ageing is caused by the gereration of polar substances such as water, acid, furfural, and so on. There is quantitative relationship between DP and the resistivity of oil-immersed paperboard.

When the typical insulation structure of 500 kV transformer based on mineral oil is directly applied to the natural ester insulating oil transformer, there are weak points of insulation that need to be improved. In this study, the safety margin of the insulation structure scheme for mineral oil was improved by increasing the main insulation distance, thickening the winding insulation, and optimizing the distribution of longitudinal capacitance of the winding. A designing scheme of insulation structure for 500 kV natural ester insulation oil transformer was formed, and simulation verification of the main insulation and longitudinal insulation of the new scheme was carried out. The results show that the scheme meets the insulation design requirements, the prototype of 500 kV natural ester insulating oil transformer developed with this scheme has successfully passed all the insulating tests.

When flashover and other accidents occur on the composite insulator in operation, the temperature rises steeply. Combined with the synergistic effect of electric field, the silicone rubber used for composite insulator will crack and destroy rapidly. In this paper, molecular model of silicone rubber was established, and then the mechanism and characteristics of electrothermal cracking of silicone rubber under steep temperature rise were studied based on the reactive force field simulation, in order to compensate for some limitations of macroscopic tests. The results show that in the flashover development stage, temperature and electric field have different mechanisms of action on the cracking of silicone rubber, temperature plays a dominant role, and electric field decreases the cracking temperature and accelerates the deterioration of material. The cracking process is triggered by the breakage of Si-C bonds, with CH₄, H₂, C₂H₄, C₂H₂, and H₂O as the main products at different stages. The number of Si-CH₃ bonds decreases by about 40% with a large number of methyl groups shed from the main chain of silicone rubber. With the further destruction of the main chain structure and the formation cross-linked structure, the number ratio of Si-O-Si bond to Si-C bond and the carbon hydrogen ratio increase continuously, the maximum is 2.93 times and 1.87 times higher than that of the pre-cracking level, respectively. The diffusion of impurity gas products dominated by H₂ generates voids in the material, leads to the structural reorganization, results in the insulation failure eventually.

During the operation of DC cable, the polarity reversal of voltage increases the space charge accumulated in the insulation, and it may damage the insulation . At the same time, the ionic charge generated by the dissociation of impurities such as cross-linking by-products introduced in the actual production process of insulating materials will aggravate the charge accumulation. Therefore, the traditional bipolar carrier transport model was improved in this paper. Considering the influence of impurity charged ions, the distribution of space charge in XLPE during the polarity reversal of voltage were simulated by using the improved transport model, and the influence mechanism of polarity reversal time and electric field intensity on charge distribution was studied. The results show that, on the basis of satisfying the mirror image distribution of space charge before and after the polarity reversal of voltage, the introduction of ionic charge increases the amount of heteropolar charge accumulated near the two electrodes in the steady state. Under the same polarity reversal time and different electric field intensity, the charge distribution law is basically the same, the higher the field strength, the more charge accumulates everywhere.

The interface charge characteristics of oil-paper insulation under DC voltage is a huge challenge in the design of the insulation structure of converter transformers. The traditional resistance-capacitance (RC) model only considers the interface polarization charges due to the different dielectric constants and electrical conductivity of oil and paper materials, ignoring other forms of charges and their effects on the space electric field. In this paper, based on Kerr electro-optic effect, a non-contact, real-time measurement platform for space electric field characteristics in oil of oil-paper insulation was built. Aimed at the composite insulation structure consist of transformer oil-electrical insulation paper and transformer oil-transformer paperboard, the space electric field characteristics in the oil under DC voltage with different polarity and different amlitude were obtained. The difference between the total interface charge density and the polarization charge density calculated by the RC model was analyzed. The results show that when the electric field intensity in the oil is low, the total interface charge is dominated by polarization charges. With the increase of the electri field intensity in the oil, the difference between the total interface charge density and the polarization charge density calsulated by RC model increases gradually, indicat other forms of charge accumulates and its proportion in total charge increases gradually, the effect of it on the electric field increases gradually.

In order to clarify the influence rule of flow velocity of transformer oil on the migration and distortion of suspended bubbles in oil under complex electric field, we analyzed the migration path and distortion degree of bubbles at different flow velocity by numerical simulation. The results show that when the oil flow velocity is lower than 0.24 m/s, the shape of bubble changes periodically, and the change frequency is about 100 Hz. The oil flow velocity is positively correlated with the offset distance form the high-pressure cone, the distortion rate, and the inner maximum electric field intensity of the bubble.

The existing detection and evaluation technology for composite insulator mainly relies on offline methods, which is difficult to assess the ageing degree of insulators in large-scale operation quickly and conveniently. This article proposes a rapid detection and rating method for surface ageing degree of composite insulators based on hyperspectral technology. At first, the Fourier infrared spectral absorption peaks of Si-O-Si and Si-CH₃ between the umbrella skirt and the substrate of aged composite insulator were compared, and then the ageing degree of insulator was rated. At last, the aging degree of insulator was classificated combining hyperspectral data with SVM algorithm models. The results show that the accuracy of the three classifications including slight, moderate, and severe is 71.8%, while the accuracy of the two classifications including sligh and severe is 97.3%. By using intensity threshold segmentation method, it is possible to remove contaminated areas from composite insulator images, and extract ageing areas.

Temperature is an important factor that affects the insulating property and the charging state of internal charging effect of insulating materials forspacecraft. In this paper, the change rule of bulk resistivity of substrate materials for satallite circuit board at different temperatures was measured by three-electrode method, on this basis, the effect of temperature on the surface charging potential and internal maximum electric field of insulating materials was simulated and analyzed by using DICTAT program. The results show that in the temperature range from -50℃to 60℃, the bulk resistivity of substrate material decreases with the increase of temperature, and its variation amplitude is more than two orders of magnitude. At the same time, the surface charging potential amplitude and internal electric field intensity of the substrate material increase with the decrease of temperature, and there is a great risk of electrostatic discharge when the temperature is lower than 0℃.

Aiming at the high risk factor of manual fault detection of strut insulators, this paper proposes a real-time fault diagnosis of strut insulators based on thermal imaging technology. The binarized segmentation of the infrared image of the strut insulator was taken as the feature extraction, and the grayscale median filter was introduced for preprocessing, then a Gaussian kernel support vector machine classification architecture was built. At last, the fault diagnosis of the strut insulator was realized. The results show that the diagnosis method can not only complete the fault monitoring of the strut insulator, but also improve the efficiency and accuracy.

In order to solve the problem that the current national standard can not fully meet the actual needs due to the imperfection and indeterminacy of the test method and judgment standard of partial discharge test of the electrical penetration assembly for reactor, on the basis of comprehensive consideration of various index requirements, we set a test scheme for partial discharge characteristics of electrical penetration assembly of medium voltage by pulse current method, and validation tests were carried out. The results show that it is reasonable to set the low value of partial discharge pulse parameter amplitude corresponding to the extinction voltage of the medium voltage electrical penetration as 15 pC, and partial discharge mainly occurs in the air gap between the multi-layer heat shrinkable tubes of its conductor components.