The frequent disconnection of inverter power devices and load characteristics of motor can lead to high-frequency pulse overvoltage, which would lead to premature failure of generator insulation and bring challenges to the stability and reliability of system. From the failure mechanism of inverter motor insulation, the different stress failure forms of inverter motor insulation were investigated firstly, and the main factors affecting the failure of the insulation system were sorted out. Then the state detection methods of inverter motor insulation and the delay measures were comprehensively reviewed. Finally, the major challenges and future research direction currently faced by inverter motor insulation were emphasized.

Epoxy resin has been widely used in the field of insulating materials due to its excellent mechanical properties, thermal stability, chemical stability, and electrical insulation. The stable three-dimensional cross-linked network structure not only gives epoxy resin excellent properties, but also brings great difficulties to its reprocessing, degradation, and recycling. At this stage, more and more researches have begun to focus on the environmentally friendly epoxy resin materials to solve problems such as reprocessing and degradation. In this paper, several typical design ideas and methods of epoxy resin based on dynamic covalent bonds were reviewed, and the environmentally friendly epoxy resin materials through introducting ester bonds, disulfide bonds, silicon-oxygen bonds, imine bonds, D-A structure, acetal bonds, host-guest interaction, and multiple dynamic bonds into the epoxy resin were introduced emphatically. Meanwhile, it is introduced that the topology structure of epoxy resin cross-linked network can be reversibly changed by dynamic covalent bonds under certain stimuli to realize the function of remodeling, reprocessing, self-repairing, and degradation. Finally, the application prospects of insulating materials based on dynamic covalent bonds were summarized and prospected.

Post insulator is an important supporting component in gas insulated metal enclosed switchgear (GIS), its insulating properties affects the reliability and stability of GIS. Taking the post insulator for engineering GIS as research object, we selected the surface tangential electric field strength of the insulator as the insulating properties index, and analyzed the influence of the umbrella skirts number, starting position, root radius, top radius parameters of the insulator as well as the shrinkage umbrella skirt structure on the insulating properties. The results show that the tangential electric field of insulator shows wave peaks and troughs oscillation distribution by increasing the umbrella skirt number, which is conducive to hinder the development of insulator surface discharge. The maximum tangential electric field strength increases with the increase of umbrella skirts number, and decreases with the increase of the distance between the starting position of umbrella skirt and the high-voltage electrode. The location of the maximum tangential electric field value shifts with the radius at the base of umbrella skirt. Compared with the original structure, the maximum tangential electric field strength along the surface of optimized structure decreases from 12.66 kV/mm to 9.69 kV/mm, and the decrease rate is 23.5%. It is found that the insulation margin is more than 1.3 times through the negative lightning impulse voltage test and margin test.

In this paper, tetracyano-benzoquinone dimethane organic small molecules with narrow band gap were introduced, and polyethylene/tetracyano-benzoquinone dimethane composites were prepared by solution blending. The effects of doping content of tetracyano-benzoquinone dimethane on DC breakdown properties, high field conductance and trap distribution properties of the composite were investigated. The results show that the electric strength of the composite increases first and then decreases with the increase of the doping content of tetracyano-benzoquinone dimethane, the addition of tetracyano-benzoquinone dimethane increases the electric strength of polyethylene by a maximum of about 54%, and effectively decreases its conductivity. Trap distribution measurement and quantum chemical simulation confirm that tetracyano-benzoquinone dimethane introduces charge deep traps, enhances the trapping effect of charge carriers, and improves the DC electric strength of polyethylene.

In the process of injection molding of the epoxy insulator on EMU roof, there will be two closing joints on the surface of the umbrella skirt along the vertical direction, the convex edges will distort the electric field near it. In this paper, the influence of the closing joint on the flashover path of the epoxy insulator on EMU roof under wet conditions was studied. Through the spray flashover test, the flashover probability between the closing joint and other parts of the umbrella skirt was compared, the motion characteristics of water droplets on the surface of the epoxy resin umbrella skirt were observed, and the effects of the closing joint on the formation of water band, electric field intensity, and current density distribution were analyzed by simulation. The results show that the flashover channel is easily form at the closing joint, and under the action of electric field, the water band near the closing joint will stretch or even bridge the adjacent skirt. The current density of water band at the closing joint of high voltage end umbrella skirt is more than one time higher than that at other parts of the umbrella skirt. The water band bridging skirt will distort the local electric field, decrease the creepage distance and increase the voltage value borne by the unit creepage distance.

COMSOL finite element simulation software was used to study the effect of bird droppings with different morphological characteristics on sulator flashover. By studying the influences of the length and viscosity of bird droppings on the flashover and the process of insulator flashover caused by the bird droppings falling, the calculation method of the combined air gap breakdown voltage composed of multiple sections bird droppings with different viscosities was obtained. The results show that the higher the viscosity of bird droppings, the better the continuity of bird droppings, the lower the breakdown voltage of the air gap, which is easy to cause the composite insulator flashover. Therefore, in order to improve the protection ability of anti-bird shield to high viscosity long bird droppings. the anti-bird shield must have the ability to reduce the length of bird droppings. In this study, a deflector groove was designed on the surface of anti-bird shield, and the high viscosity long bird droppings can be divided into several sections of short bird droppings through the deflector groove. By reducing the length of bird droppings, the air gap length increases, so as to increase the breakdown voltage and decrease the probability of bird droppings flashover.

The research on the pyrolysis gas generation law of cable can provide a basis for cable fire early warning. In this paper, a high temperature pyrolysis experiment platform was set up for common cables. The pyrolysis gas generation laws of PVC outer sheath of cables at 75, 100, 120, and 150℃, as well as the pyrolysis gas generation laws of cable internal materials at 185℃ and 225℃ were studied, respectively. The results show that PVC outer sheath of cables has been pyrolyzed at 75℃, and the pyrolysis gases are CO and CO₂. When the temperature is below 120℃, the pyrolysis gas components are only CO and CO₂, so CO and CO₂ are suitable as early characteristic gas components for commonly used cable fires. When the temperature is 150℃, gas components such as CH₄, C₂H₄, C₃H₆, and CH₃Cl appear in the pyrolysis gas, so the CH₄, C₂H₄, C₃H₆, and CH₃Cl can be used as the characteristic gas components of cable overheating faults.

In order to improve the cracking resistance of the encapsulating insulating material for dry-type air-core reactor, it is necessary to improve the toughness of the epoxy resin composite while ensuring the good electrical properties. In this paper, an epoxy glass fiber composite with good mechanical and electrical properties was obtained by adding different content of epoxy-terminated liquid nitrile butadiene rubber (ETBN), different content and partical size of Al₂O₃ powders to the epoxy glass fiber (EP/GF) composite, and its structure and morphology, mechanical and electrical properties were tested. The results show that when the mass fraction of ETBN, 5 μm Al₂O₃, and 100 nm Al₂O₃ is 10%, 30%, and 3%, respectively, the bending strength of the EP/GF composite reaches the highest of 291.0 MPa, which increases by 33.5% than that of the unmodified composite, and the electric strength is 24.3 kV/mm, the comprehensive properties are the best.

DC cable mainly uses oil-paper and crosslinked polyethylene (XLPE) as insulation, and the conductivity characteristics of the two materials are different, which has a significant effect on the electric field distributions in cable. In this paper, a finite element model was established based on the 500 kV typical DC cable structure, and the thermal-electrical coupled simulation analyses were performed on the oil-paper and XLPE insulated cables. The electric field distribution characteristics in the two insulation under different temperatures and temperature drops were studied, and the influences of the conductivity temperature and electric field coefficient on the field strength distribution were analyzed. The conductivity variations of oil-paper and XLPE insulations among the same temperature and field ranges were compared. The results show that the electric field distribution in oil-paper insulation is affected by the insulation temperature difference in the electric field strength range of 10-25 kV/mm and temperature range of 20-90℃, and hardly changes with the insulation temperature under definite temperature difference, while the electric field distribution in XLPE insulation is affected by both insulation temperature and temperature difference. In addition, the overall conductivity of oil-paper insulation is higher than that of XLPE insulation, and its change amplitude with temperature and field strength is larger, which may be the reason why the electric field inversion in oil-paper cable insulation occurs at a lower temperature difference. For the insulating materials used in HVDC cables, the conductivity temperature coefficient should to be controlled small so as to reduce the temperature sensitivity.

Polyvinylidene fluoride (PVDF)-based polymer has promising applications perspectives in the field of high energy storage density and high pulse energy storage. In this paper, barium titanate (BTO) nanoparticles were doped with polyvinylidene fluoride-chlorotrifluoroethylene (P(VDF-CTFE)) solution, and P(VDF-CTFE)/BTO composite films were prepared by solution casting method. The effects of different BTO doping contents on microstructure, dielectric properties, and energy storage characteristics of the composite films were investigated. Then the BTO was modified by dopamine (DA) to enhance the compatibility between BTO and polymer matrix and improve the dielectric constant and electric strength of composite films. At the same time, on the basis of the "breakdown blocking effect" between the films layers, the laminated composite films were prepared to enhance the energy storage properties. The results show that using the P(VDF-CTFE)/DA@BTO composite film with a DA modified BTO mass fraction of 10% as the interlayer, and the P(VDF-CTFE) as the outerlayer, the prepared PV-BT-PV laminated sandwich composite film has a dielectric constant of 10.44, a maximum electric strength of 362.25 kV/mm, and a charge discharge efficiency of 86.63% at an electric field strength of 500 kV/cm.