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.

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.

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.

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.

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.

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.

Compared with mineral insulating oil, natural ester has the advantages of higher ignition point, better degradability, and can delay the thermal ageing rate of insulating paper, so natural esters are receving extensive attention as liquid insulating medium for extending the life of transformers or improving short term overload capacity. In this paper, we used rapeseed oil, which accounted for a large proportion of cooking oil in China, to prepare rapeseed oil based natural esters, and the accelerated thermal ageing characteristics of insulating paper with different water contents in rapeseed oil based natural ester and mineral oil were investigated. The effect of oxygen on the accelerated thermal ageing characteristics of insulating paper in the two different insulating liquids was studied. The experimental results show that at the same temperature, water content is the main factor affecting the thermal ageing rate of insulating paper, and oxygen will reduce the inhibitory effect of rapeseed oil based natural esters on the thermal ageing rate of insulating paper with low water content. Combined with the measured data of specific strength and degree of polymerization of insulating paper during thermal ageing in insulating liquid, a kinetic model of cellulose decomposition reaction rate of insulating paper considering the influence of water content and oxygen was established. The model can be used to predict the thermal ageing process of insulating paper in insulating liquids.

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.

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℃.