Under the background of “carbon peaking and carbon neutrality” development strategy goal, in order to explore the application prospects of green and environment friendly bio-based epoxy resins in electrical equipment, a bio-based resin of maleopimaric-based epoxy resin (MPAER) was prepared using a renewable resource of rosin as raw material. Taking methylhexahydrophthalic anhydride (MHHPA) as the curing agent, we systematically studied the curing characteristics, as well as the thermal, mechanical, and electrical properties of the MPAER/MHHPA system, and the MPAER/MHHPA system was compared with the DGEBA/MHHPA system composed of commercial diglycidyl ether of bisphenol A (DGEBA). The results show that the MPAER/MHHPA system and DGEBA/MHHPA system have equivalent curing reaction activity. The glass transition temperature of the MPAER/MHHPA system is 112.8℃, its mechanical and electrical properties are slightly weaker than those of the DGEBA/MHHPA system, and its electric strength is 9.4% lower than that of the DGEBA/MHHPA system. However, the comprehensive performance of the MPAER/MHHPA system is still good, and its performance can be further improved by optimizing the structure of MPAER or blending with other types of epoxy resins.

Thermosetting epoxy resin is widely used in electrical equipment field due to its excellent thermal conductivity and insulating properties. Due to the stable three-dimensional network structure and insolubility of the thermosetting epoxy resin, its recycling and reuse pose challenges. In this paper, we added different mass fractions of boron nitride (BN) into the epoxy (EP)/4-methylhexahydrophthalic anhydride degradation system to prepare high thermal conductivity, high insulating, and degradable BN/EP composites, and studied their thermal conductivity, dielectric properties, and degradability. The results show that taking 2,4,6-tris(dimethylaminomethyl) phenol as the catalyst, the EP/BN composites can achieve atmospheric pressure degradation at 200℃ under the action of ethylene glycol. The thermal conductivity of BN/EP composite with 15% mass fraction of BN is 0.335 W/(m·K), which is 34% higher than that of pure EP resin; the AC electric strength is 101.7 kV/mm, which is 13% higher than that of pure EP resin. BN/EP composites can be degraded through transesterification to obtain EP degradation products (EDP). After the BN/EP composites are compounded with EDP, the thermal conductivity and electric strength of the BN/EP composites is basically unchanged.

The mechanical properties of insulation pressboard are key factors in modeling the structure of transformer windings. The operating transformer winding is subjected to periodic electromagnetic forces, and the static stress-strain test results cannot characterize the dynamic mechanical properties of insulation pressboard. In this paper, an asymmetric hysteresis model was proposed to study the dynamic mechanical properties of the insulation pressboard under periodic electromagnetic forces, and the model includes not only linear damping and stiffness coefficients, but also nonlinear dynamic stiffness. In the experiment, a pneumatic vibration exciter was used to simulate the amplitude and frequency of the electromagnetic force, and the stress-strain data of the insulation pressboards under different clamping forces was obtained. A multi-objective optimization algorithm based on NSGA-II algorithm was used to train the model parameters. The results show that the stiffness and damping of the insulation pressboard are closely related to the clamping force, and the oil-immersed pressboard has obvious damping characteristics. As the clamping force increases, the dynamic stiffness of the insulation pressboard decreases during the loading and unloading processes. Compared with the amplitude of periodic electromagnetic force, the frequency of periodic electromagnetic force has more significant effect on the mechanical characteristics of insulation pressboard.

Natural ester and synthetic ester insulating oils are getting more and more application in transformer industry because of their eco-friendly and excellent fire resistance characteristics. At present, there is no precedent in China for the application of environment friendly ester insulating oil in 220 kV power transformers for offshore substation. According to the characteristics and requirements of offshore substation, the selection of transformer ester oil types and insulation system types were studied in this paper. Taking SZ-150000/220 type transformer as the object, an improved model of the transformer body structure was established for simulation analysis, and the simulation results show that the ester insulating oil meet the requirements of insulation and temperature rise of 220 kV power transformer. The feasibility of ester insulating oil applied in 220 kV power transformer for offshore substation was discussed through comparative analysis and simulation calculation, and an optimized design scheme was proposed to make the equipment adapt the requirements of offshore operating environment, which provides a reference for the application of ester oil transformer in offshore substation.

In this paper, the modeling methods of three-capacitance model, conductance model, and plasma model for the numerical simulation of partial discharges under DC voltage and their advantages and disadvantages were introduced, and the recent research achievements of experts and scholars at home and abroad using these models were reviewed. The researches on partial discharge testing under DC voltage in the recent years was summarized, and the impacts of temperature, insulation material, voltage harmonics, atmospheric pressure, and defect on the partial discharge charactristic under DC voltage were summarized. Finally, the limitations of current numerical simulation studies were discussed, and the potential areas for further research were prospected.

To explore the moisture characteristics of the cold shrink intermediate joint for distribution cables at the current stage, undamped joints samples were made firstly in this paper. Accelerated moisture ageing platform was used to treat the samples with moisture. Then the polarization and depolarization current (PDC) test system was used to test the polarization and depolarization currents of the samples which damped for 0, 2, 4, 6, and 8 weeks. At last, their DC conductivity was calculated, and the time constant of three branches was obatined by branch identification. The experimental results show that the DC conductivity of intermediate joint will change only after the joint has damped to a certain extent. The third branch time constant decreases with the increase of moisture degree. This is because the moisture reduces the interface charge migration resistance, which would reduce the interface polarization time. Therefore, the third branch time constant can sensitively reflect the moisture degree of the cable intermediate joint, which can be used as the characteristic parameter to judge the moisture degree of the cable intermediate joint.

A high-performance organsilicone encapsulant was prepared with vinyl silicone oil interchange as base polymer, hydrogen-containing silicone oil as crosslinker agent, fumed silica and MQ silicone resin as reinfocing materials, magnesium hydroxide and FCA107 as flame-retardant filler. The effects of the ratio of between Vi-PDMS and Vi-PMVS and filler content on the properties of organsilicone encapsulant were discussed. The results show that when the ratio of between Vi-PDMS and Vi-PMVS is 5:5, the mass fraction of vinyl silane coupling agent is 4%, the mass fraction of MQ silicone resin is 30%, the mass fraction of compound flame retardant is 20%, the organsilicone encapsulant has optimum comprehensive performance. The mixed viscosity is 1 842 mPa·s, the tensile strength is 2.83 MPa, the elongation at break is 51.3%, the shear strength is 2.12 MPa, the flammability rating is UL 94 V-0, the dielectric strength is 24.3 kV/mm, and the volume resistivity is 3.8×10¹⁵ Ω·cm. The prepared organsilicone encapsulant could satisfy the development demands of electronic components.

The frequent faults caused by buffer layer defects in high-voltage cross-linked polyethylene cables have seriously threatened the safe operation of power system. In this paper, the basic structure and function of buffer layers was introduced at first, and the relevant research on buffer layer failure at home and abroad were summarized. Secondly, the main reason of buffer layer defects was analyzed through electric field simulation from the material characteristic and internal structure of buffer layers, and the insulating properties and physicochemical characteristics of the white powder in buffer layer were summarized to propose its formation mechanism. Finally, the detection methods of buffer layer defects were summarized, it is proposed to use computer tomography technology to detect cable buffer layer defects to make up for the shortcomings of existing detection methods, and it is recommended to optimize the materials or structures of aluminum sheaths and buffer layers to prevent the generation of buffer layer defects.

In order to improve the toughness and solubility of bismaleimide resin and improve its application in the field of high frequency and high speed copper clad laminate, a silicone modified bismaleimide resin (Si-D936) was designed and synthesized from silicone and D936 type bismaleimide in this paper. The characteristic structure of Si-D936 and silicon-D936 monomer were characterized by IR, NMR, and gel permeation chromatography. Additionally, the effects of different silicon contents on the solubility, heat resistance, mechanical properties, and dielectric properties at 10 GHz of the Si-D936 were explored. The results show that compared with the modified D936, the solubility of Si-D936 in butanone is obviously improved, and the highest solubility can reach 30% (at room temperature). However, with the increase of Si content, the molecular weight of Si-D936 increases, and the solubility decreases slightly. The Si-D936 modified resin has good thermal properties after curing, but the heat resistance and residual carbon rate decrease gradually with the increase of Si content. The silicone modification can improve the mechanical properties of D936 resin, in which the impact strength and tensile strength of Si-D936-1 (the molar ratio of D936 to HMM is 3:1) increase by 35% and 24.6%, respectively. However, with the further increase of Si content, the cross-linking degree of the modified resin is affected, and the impact strength, bending strength, and tensile strength of the modified resin decrease. After silicone modification, the dielectric properties of the modified resin are improved, and the dielectric loss is reduced from 0.009 4 to 0.007 2 (10 GHz).

High-temperature-vulcanized (HTV) silicone rubber has poor resistance to ultraviolet (UV) ageing, and its hydrophobicity would gradually lost, tensile strength decrease, and hardness significantly increase after ultraviolet irradiation. In order to improve the hydrophobicity and UV resistance of HTV silicone rubber, the permanent-room-temperature-vulcanized (PRTV) silicone rubber and four needle-like zinc oxide/nano-zinc oxide (tZnO/nZnO) particles with different structures were introduced onto the surface of HTV silicone rubber by embedding-curing method to prepare the hydrophobic and anti-UV composite coatings with different morphologic morphology. The effects of the composition of composite coating on the microstructure and anti-ageing properties of HTV silicone rubber were studied by the ageing experiment and water contact angle, surface hardness, and mechanical properties tests. The results show that the surface holes of HTV silicone rubber are covered, its hydrophobicity increases, and water content and water absorption decrease after the introduction of PRTV silicone rubber on the surface of HTV silicone rubber. The further introduction of ZnO particles greatly improves the hydrophobicity, UV resistance, and thermal stability of HTV silicone rubber materials. The PRTV silicone rubber-tZnO/nZnO composite coating introduced by stepwise embedding-curing method can effectively construct a micro-nano mastoid structure and UV shielding layer on the HTV silicone rubber surface, and its enhancing effect on the hydrophobicity and UV ageing resistance are more obvious than that of single embedding of tZnO or nZnO particles.