Ethylene-vinyl acetate copolymer/ethylene-α-olefin copolymer (EVA/POE) was used as the base material, and phosphorus-nitrogen halogen-free flame retardant (HF-601AE) compounded with surface modified aluminum hydroxide (ATH) was used as the flame retardant system, a halogen-free flame retardant polyolefin material for heat shrinkable tube was prepared by melt mixing method. The variation of limiting oxygen index, electrical properties, and mechanical properties of the composites under different ratios were studied, and the flame retardant mechanism of composites was investigated by thermo-gravimetric analysis (TGA) and the morphology characterization of combustion residue carbon. The results show that and the 2^# sample prepared with 50 phr polyolefin materials, 35 phr flame retardant HF-601AE, and 20 phr ATH has the best mechanical properties, and the tensile strength is 7.1 MPa, the elongation at break is 502.86%. The limiting oxygen index is 37.2%, which meets the requirements of EN45545-2 R22 HL3 flame retardant grade. The thermogravimetric rate at 371.5℃ reaches -18.11%/min, the carbon residue is low after combustion, and there are no holes and pores in the carbon layer, which indicate that the comprehensive properties are the best.

In order to improve the upper limit temperature and high temperature stability of BaTiO₃ for MLCC insulating dielectric material, a Ba_1-xCa_xTiO₃ nano-powder was prepared by using BaCl₂·H₂O, CaCl₂, and H₂TiO₃ as raw materials and KOH as mineralizer under the condition of 210℃/22 h hydrothermal reaction. The phase structure, microstructure, and dielectric properties of the samples were characterized and analyzed by XRD, SEM, LCR detection methods. The results show that the obtained powders are uniformly dispersed and the particle size is (110±20) nm. The doping of Ca²⁺ increases the Curie temperature of BaTiO₃, and a Ba_0.91Ca_0.09TiO₃ ceramics with 136.2℃of Curie temperature, 1 882 of dielectric constant, and 0.02 of dielectric loss factor are obtained at 1 250℃/2 h. The preparation of MLCC insulating dielectric materials with small particle size, narrow distribution, low agglomeration, and high performance is realized.

In order to effectively adsorb the corrosive sulfur in transformer oil, XDK was used as adsorption material, and dibenzyl disulfide (DBDS) was used as the experimental object. The test oil was prepared by adding DBDS to new transformer oil. The removal effect of XDK on DBDS in test oil was studied under different adsorption conditions and regeneration conditions. The structure of XDK was characterized by scanning electron microscopy (SEM), thermogravimetry (TG), and specific surface area analyzers (BET). The results show that the optimal regeneration temperature of XDK is 600℃, and the regeneration XDK still has good adsorption effect after four times. When the XDK mass fraction is 10%, the adsorption times are two times, the adsorption temperature is 10℃, and the adsorption times is 2 h, the DBDS removal rate reaches 96.9%, the dielectric constant, breakdown voltage, and volume resistivity of the insulating oil after treated increases by 0.31%, 5.3 kV, and 0.23 Ω·m, respectively, and the dielectric loss factor decreases by 0.21%.

In this paper, the performance and characteristics of low smoke halogen-free flame retardant cable material was reviewed. The advantage and disadvantage of ethylene-vinyl acetate copolymer (EVA) as the base material was introduced.The types and flame retardant mechanism of halogen-free flame retardant were reviewed. Finally, the development direction of low smoke halogen-free flame retardant cable material was prospected.

In order to obtain carbon-ceramic linear resistor with stable performance, the preparation of high resistance layer glaze slurry used in the manufacturing of carbon-ceramic resistor was studied systematically in this paper. Firstly, the glazing technology of glaze slurry prepared by different binders was compared, then the mixing time and water material ratio of slurry were systematically studied to obtain the influence of mixing time and water material ratio on the viscosity of glaze slurry, and finally the optimal mixing process parameters were determined. The results show that the glaze slurry has good suspension and coating properties when the Zuoyun clay is used as binder. When the mass fraction of Zuoyun clay is 15%, the glaze slurry has good processability and adhesion. The optimum mixing process parameters of high resistance glaze and binder is as below: Zuoyun clay is used as binder, the mass fraction of clay is 15%, the ratio of water and material is 0.6∶1, and the mixing time of ball glaze is 1 h. The breakdown strength of carbon-ceramic resistors coated with high resistance layer is 78% higher than that of the uncoated resistors, and the dispersion is smaller.

Medium frequency transformers have high power density, small volume, complex winding structure, and strong local electrical stress, so the design of transformer must fully consider the electro-thermal stress margin to ensure reliability. In this paper, the method of adding electrostatic ring and angle ring were proposed to suppress the electric field strength at the end of primary winding, and the electric field strength distribution of multi-winding transformer was calculated by electrostatic field finite element analysis method. Combined with the sensitivity analysis method, the influence of the size parameters of electrostatic ring and angle ring on the electric field strength was studied to determine the decisive factors of the maximum electric field strength. The response surface function related to electric field strength was constructed by response surface method to optimize the insulation structure of transformer. The results show that the optimal sizes of electrostatic ring and angle ring are obtained by the above response surface function through taking a 50 kW, 10 kHz multi-winding medium-frequency transformer as an example, which can reduce the maximum electric field strength by 15.4% and 17.49% under short-term power frequency withstand voltage test and rated operating conditions, respectively. It is proved that the response surface method can be applied to the insulation structure design of multi-winding transformer.

Partial discharge type is closely related to the early insulation deterioration degree of power capacitor film. The accurate identification of partial discharge type will effectively improve the operation state of capacitor and guarantee the safety of power grid. In this paper, the models of inter-film tip defects, air gap defects, and surface defects generated easily in metallic film capacitor were designed. The time series and phase distribution spectra characteristics of partial discharge in capacitor film and the development of average discharge quantity Q and discharge repetition rate F were analyzed. The curves of Q and F were fitted with points, and the correlation between them and partial discharge signal was analyzed. The correlation coefficient was taken as the characteristic parameter of time domain. The skew, steepness, and asymmetry of partial discharge phase distribution spectra were extracted as phase characteristic parameters. A partial discharge pattern recognition method of power capacitor film based on time-phase synthetic radar spectrum was proposed. The barycentric coordinates of the enclosed rectangle of characteristic parameters closed graph in the synthesis spectrogram were conducted cluster analysis, and the distribution quadrants of barycentric coordinates were used to recognize the partial discharge pattern of film. The results show that the method has more pattern recognition accuracy than the traditional single spectrum, which provides a theoretical basis for online monitoring and fault diagnosis of capacitor equipment.

Partial discharge (PD) phenomenon in power transformer is not only the main cause of insulation deterioration, but also the characteristic parameter to characterize the insulation condition. It is of great significance to accurately recognize the type of PD for the diagnosis of transformer insulation condition. A new method for identifying the type of multi-source PD spectrum based on Faster-RCNN algorithm was proposed in this paper, which can detect different types of PD clusters from multi-source spectrum. The results show that the average recognition accuracy of multi-source PD reaches 72.1% when the proposed algorithm was applied to the PD spectrum obtained from 35 kV transformer. Because the air gap defect has dense PD points and obvious characteristics, its missed and false detection rates are lower than other defects, leading to there be good discrimination for the air gap defect. Because the tip defect has the characteristics of intermittent discharge and high initial discharge voltage, its missed detection rate is high.

To investigate influence of high-altitude environment on the electrical ageing performance of the main insulating material of new energy vehicle (NEV) drive motor, NHN insulating paper was selected as the main research object. According to the actual working conditions of NEV, the NHN insulating paper was applied bipolar repeated square waves, and its partial discharge inception voltage (PDIV) under different air pressures was measured. The PDIV value under standard atmospheric pressure was used as standard voltage, and 1.5 times of standard voltage was applied to the samples under different air pressures. The physical and electrical parameters of the samples under the condition of electrical ageing for 30 minutes and ageing to breakdown were measured, and the ozone content generated during the electrical ageing process was detected. The results show that the PDIV value of the main insulation sample decreases significantly under low pressure, and when the applied voltage is greater than the PDIV, the sample surface is corroded more severely compared with the plain area, leading to the sample break down easier. During the electrical ageing process with the same time and voltage, the electrical parameters of the samples under low pressure have bigger change, the ozone production rate of partial discharge is faster, the corrosion of the material is intensified, and the deterioration of insulating properties is more serious. Based on above studies, the influence of altitude factors on the corona resistance performance of insulating materials should be fully considered when designing the insulation system of motor for NEV.

Inter-turn short circuit is the main fault type of dry-type air-core reactors. At present, there is a lack of effective offline detection method to discover potential faults in time before dry-type reactors put into operation. Based on the theory of multiconductor transmission line, a distributed parameter model of dry-type air-core reactor winding was built to simulate the refraction and reflection processes after pulse signal injection, and the influence law of inter-turn short circuit on the response signal at the head and end of winding was discussed. On this basis, a characteristic waveform was constructed by the integral value of response signal absolute value, and a characteristic value was extracted to diagnose the inter-turn insulation state of winding. The results show that the test results of four-eigenvalue method proposed in this paper based on the wave process and multiconductor transmission line theory are consistent with the simulation results. Through the simulation calculation of different structural reactor models, it is found that the eigenvalue change trend of different structural reactor is also consistent when the inter-turn short circuit fault occurs. Therefore, the above method can be applied to diagnoze the inter-turn short circuit fault of reactors with different structures. The research results can provide guidance for the diagnosis of the severity and regional localization of inter-turn short circuit in dry-type air-core reactor.