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).

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.

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.

Low-frequency cable is a key equipment in the flexible low-frequency AC transmission system, and the characteristics of insulation medium under low-frequency voltage are of great significance to the design and operation of cable. In order to study the growth and partial discharge characteristics of electrical tree in cross-linked polyethylene under low-frequency voltage, a real-time observation system for electrical tree growth at different frequencies and a synchronous measurement system for partial discharge were designed and constructed. The initiation, growth, and partial discharge characteristics of electrical tree in XLPE samples were investigated at four frequencies of 20, 30, 40, and 50 Hz. The results show that the influence of voltage frequency on the growth and partial discharge characteristics of electrical tree in XLPE has obvious rules. In the range of 20-50 Hz, with the decrease of voltage frequency, the tree starting voltage of XLPE increases slightly, but the growth rate of electrical tree is accelerated, the damage area increases, the amount and number of partial discharge increase, and the partial discharge phase is basically unchanged.

In hot and humid environment, composite insulators with interface defects are more prone to occur serious accidents such as decay-like breakage and interface breakdown. However, there is a lack of studies on the interface ageing mechanisms of composite insulators with core-sheath interface defects under hygrothermal environment. In this paper, composite insulator short samples with different interface defects were subjected to hygrothermal ageing. The temperature rise and discharge results of each sample were compared under conditions of moisture absorption and dry condition. The influence of hygrothermal environment on the performance of composite insulators with interface defects was studied through dissection observation, microscopic morphology observation, and surface elements and functional groups analysis. The results show that the insulator interface defects will expand into interface failures under the action of heat and humidity. Partial discharge and polarization loss of moisture at the interface will trigger abnormal heating faults, and the temperature rise caused by metal defects is significantly higher than that of other defects. As the interface defects gradually expand, epoxy resin undergoes oxidation and decomposition from interface to interior, and the glass fibers exposes and deteriorates.

In order to solve the problem of turn-to-turn insulation for oxygen-free copper coils in radio frequency plasma of antenna built-in type, a process capable of sintering a glass insulating layer on the surface of oxygen-free copper was studied, and the effects of factors such as different surface treatment method, binder, and sintering temperature of the process on the performance of glass insulating layer were investigated in detail. The results show that the oxygen-free copper surface after acid washing pretreatment can significantly improve the wettability of low-temperature glaze on the copper surface compare to alkali washing, and reducing the "porosity" on the insulating layer surface. At the same time, an appropriate adding amount of Na₂SiO₃-5H₂O binder can improve the interface combination effect between the glass insulating layer and the copper surface, and improve the hardness of glass insulating layer surface. In addition, the surface hardness of the insulating layer increases with the increase of the sintering temperature, and the number of "porosity" on the insulating layer surface is gradually reduced. An oxygen-free copper coil antenna with a glass insulating layer on the surface was finally prepared according to this process, which achieved a long-time discharge maintenance and effectively solved the turn-to-turn insulation problem during discharge process.

The use of silicon carbide (SiC) inverters for power supply can reduce the size, weight, and temperature rise of traction inverter motors and improve the motor efficiency. However, the high frequency and short rise time of the inverter output voltage would bring challenges to the insulation of traction inverter motors. The turn-to-turn insulation will be subjected to higher voltage loads, which will lead to premature insulation failure. In this paper, the voltage waveforms of turn-to-turn insulation of high-voltage inverter traction motor were firstly simulated when the SiC inverter is at the maximum switching frequency and the actual cable length. The partial discharge inception voltage (PDIV) test and endurance life test were conducted on the electromagnetic wire of high-voltage inverter motor under different voltage parameters (frequency, voltage level, rise time), different temperatures, and different thicknesses of turn-to-turn insulation (0.23 mm, 0.30 mm). Then according to the actual operating conditions of traction motor and the electrical load failure mechanism of insulation system, the change mechanism of PDIV, partial discharge characteristics, and life was analyzed. The PDIV test results show that the change of frequency and rise time has no influence on the PDIV. The PDIV derceases with the increase of temperature. However, due to the fabrication process, the PDIV increases at some temperatures. The increase in thickness has a greater increase in PDIV. Under the premise of controllable cost and efficiency, increasing the thickness can effectively improve the turn-to-turn insulation performance of inverter motors. Endurance test results show that the changes in temperature and rise time would cause large changes in insulation life. The effect of frequency and voltage level on insulation life is non-linear, and it can be expressed by the inverse power model. In industrial applications, the effect of frequency on the insulation life can be directly converted through a proportional relationship.

Cross-linked polyethylene (XLPE) is subject to various environmental or human factors during production, laying, and operation, which can generate structural defects at different scales and affect the electrical performance of XLPE. In this paper, the molecular defects, aggregated structural defects, and macroscopic air gap defects in XLPE power cables were reconstructed and characterized by X-ray Diffraction (XRD) and transmission and reflection modules of terahertz time-domain spectroscopy (THz-TDS). The results show that the amplitude and phase information of terahertz time-domain spectroscopy exhibit sensitive to the structural changes of polar molecules and aggregates, respectively. The location and size of hidden air gap defects can be accurately identified and calculated by the combined technique of transmission and reflection modules of terahertz time-domain spectroscopy, realizing the nondestructive detection of defects at different scales.

The stable operation of dry-type reactors affects the transmission reliability of new power system. The encapsulating material of dry-type reactor is made of glass fiber filament impregnated epoxy resin cured at high temperature. In this paper, a multiphysics coupled finite element method was used to consider the influence of thermal conductivity of the encapsulating material for dry-type reactor on its hot spot temperature rise, and a COMSOL microscopic simulation model of epoxy composites and an electro-magnetic and flow-thermal coupling calculation model of dry-type reactor under the constraints of external circuits were established. The temperature field and flow field distribution were calculated by using the loss under electromagnetic field as the heat source, and the influence of conventional/high thermal conductive epoxy composites on the hot spot temperature rise of the dry-type reactor at 25℃ of ambient temperature was studied. The results show that the high thermal conductive epoxy resin has a significant improving effect on the thermal conductivity of composites. The maximum hot spot temperature rise in the temperature field area of the encapsulating material body and the surrounding air is 103.75℃, which appears at the upper end of the fourth layer of encapsulating material. The epoxy resin composite with different thermal conductivity has obvious difference on decreasing the hot spot temperature of dry-type reactor, and the hot spot temperature of the dry-type reactor with high thermal conductive epoxy resin composite is reduced by 7.55℃.

In oil-immersed systems, the rapid development of discharge faults has the characteristic of high gas production and fast gas generation rates. As a result, the generated characteristic gases may not have enough time to dissolve in oil. The majority of these gases escape to the oil surface and enter the gas relay, leading to that a large amount of effective gas for transformer diagnosis and early warning is unable to reach dissolution equilibrium in time, which makes the commonly used dissolved gas analysis method in power industry unable to accurately diagnose faults. Based on this, an experimental platform for studying the gas production law on the oil surface under fast-developing discharge faults of oil-immersed insulation system was constructed. The characteristic gas information on the oil surface of the oil-immersed insulation system during fast-developing discharge faults was obtained. The results show that the concentration of characteristic gases in the liquid phase does not increase significantly in the short period after fault occurred, while there is a large amount of characteristic gases in the gas phase at this time. When there is high-energy discharge in the system, CO, CO₂, CH₄, and H₂ will accumulate on the oil surface, and these four gases can be used as characterization basis for high-energy discharge faults. On this basis, C₂H₆, C₂H₄, and C₂H₂ will also accumulate on the oil surface when there is spark discharge, and these three gases can be used as diagnostic basis for spark discharge.