Considering the heat transfer and charge accumulation process in DC GIL comprehensively, we established an electro-thermal multi-physics field coupling model of DC GIL. On the basis of this model, the effect of the volume conductivity of insulating materials on the surface charge accumulation of basin type insulator was simulated and calculated under the coupling action of DC electric stress and thermal stress. The results show that the surface charge accumulation of insulator can be inhibited effectively by decreasing the volume conductivity of typical insulating materials for current AC basin type insulator by two orders of magnitude. However, if the volume conductivity of insulating materials decreases excessively, the surface charge accumulation of basin insulator will be aggravated.

First of all, hexagonal boron nitride (h-BN) micro-powder and sericite micro-powder (Mica) were used as raw materials, boron nitride nanosheets (BNNSs) and mica nanosheets (MNS) were exfoliated by freeze-thaw cycle combined with ultrasonic technology. Then the BNNSs and MNS were used as insulating thermal conductive fillers, mica/boron nitride nanohybrid polyimide films (MNS/BNNS nanohybrid PI films) were prepared by in-situ polymerization and two-step water-based polyimide (PI) process. The influence of different MNS/BNNS filling amounts on the performance of PI composite films was studied. The morphology and structure of BN, BNNS, Mica, and MNS were characterized by XRD, TEM, and AFM, and the thermal conductivity, dielectric constant and electric strength of the MNS/BNNS nanohybrid PI films were measured. The results show that when the ratio between MNS and BNNSs is 1∶2, the MNS/BNNS nanohybrid PI films have better comprehensive properties, and the thermal conductivity is significantly improved compared with pure PI. The thermal conductivity is 0.743 W/(m·K), the electric strength is 246 MV/m, and the dielectric constant is 5.28.

PTC resistance device, which made by positive temperature coefficient (PTC) material, can be used as a passive component to prevent overcurrent fault. In this paper, four kinds of polymer-based PTC materials were prepared by melting blending method, and the effects of conductive filler concentration, coupling agent, and supplementary conductive filler on their properties were studied. According to the temperature-resistance characteristics and heat transfer equation of polymer PTC composite, its current limiting process was simulated. The experimental results show that increasing the concentration of conductive filler will lead to the decrease of the resistivity of composite at room temperature. The PTC properties of the composites can be improved by using silane coupling agent to modify CB and adjusted by the interaction of various fillers. The simulation results show that under certain assumptions, the PTC resis-tor, as a passive component to prevent overcurrent fault, can limit the short-circuit current of power system in a short time.

In order to study the effect of micron particle fillers on the thermal conductivity of filled type high thermal conductive composites, we constructed a finite element model of composites with randomly distributed particle fillers in this study. The effects of filling ratio, particle size, thermal conductivity, particle shape of filler on the thermal conductivity of the composites were calculated and discussed, respectively. The results show that with the increase of filling ratio and length-to-diameter ratio of filler particle, the thermal conductivity of the composites increases significantly. The particle filler size has little effect on the thermal conductivity without considering the interface thermal resistance and particle agglomeration. The thermal conductivity of filler has little effect on the thermal conductivity of the composites. Without considering the interface thermal resistance, whether the heat conduction channel can be formed effectively is the key to determine the thermal conductivity of the filled type composites.

The thermal conductive and insulating composite material with polymer matrix and high thermal conductive filler is an ideal solution to settle insulation protection of live working equipment and heat dissipation problem of electrical and electronic equipment. In this study, micron alumina (Al₂O₃), surface modified by silane coupling agent KH550, mixed with high thermal conductive carbon nanotubes (CNT) as thermal conductive filler, silicone rubber (SR) with wide temperature range resistant and corrosion resistant was selected as polymer matrix, an SR composite material was prepared, and its performance was tested. The results show that when the total content of Al₂O₃/CNT mixed filler is 10%, the proportion of carbon nanotubes is 0.2%, the thermal conductivity of the SR composite is as high as 0.268 W/(m·K), which is improved by 103.1% compared with SR, the resistivity is 10.5×10¹² Ω·cm, the relative dielectric constant is almost unchanged, and the Shore hardness A and Young’s modulus increase slightly .

A silicon carbide/organic montmorillonite/epoxy resin micro-nano non-linear corona resistant composite material was prepared. The influence of silicon carbide and organic montmorillonite content on the dielectric properties of the corona resistant material was studied. Bars were prepared using the corona resistant material, and their corona resistance and surface temperature were tested. The results show that the addition of a certain amount of nano organic montmorillonite could effectively improve the non-linear characteristic of the corona resistant composite, reduce the surface temperature of anti-corona area, and improve the corona resistance of bars.

In order to improve the thermal conductivity and environmental resistance of motor insulation system, we analyzed the conventional properties, heat resistance, thermal conductivity, and environmental resistance of a high thermal conductive and high temperature resistant epoxy encapsulating resin. A prototype was made, and the application performance of the epoxy encapsulating resin in low voltage motor was tested. The results show that the epoxy encapsulating resin has excellent mechanical and electrical properties, excellent low temperature and thermal shock resistance, and good compatibility with enameled wire, and the thermal conductivity and temperature index reach 1.18 W/(m·K) and 187.5℃, respectively. The application of high thermal conductive insulating resin could effectively improve the thermal conductivity of the motor insulation system, under the same conditions, the temperature rise of motor decreases by 20.7℃ compared to the motor with ordinary high temperature resistant insulating varnish. At the same time, compared with the vacuum pressure impregnation process, the insulation system of the motor made by the vacuum encapsulation process has better integrity, electrical properties, and humidity resistance, and the disadvantage of low paint hanging at the groove is avoided.

In order to develop a high thermal conductive epoxy potting adhesive for dry-type transformer, we prepared a potting adhesive by adding self-made modified silica to epoxy anhydride system. The thermal conductivity and electrical insulation performance were tested, and the suitable pouring temperature and best curing process of the potting adhesive were studied. The results show that when the filling content is 75%, the potting adhesive has high thermal conductivity and excellent electrical insulation performance, the thermal conductivity is 1.494 W/(m·K), the dielectric loss factor is only 0.41%. When the pouring temperature is 70℃, the potting adhesive has good pouring process, the viscosity is low than 2 800 MPa·s within 2 h. The best pouring process for potting adhesive is 80℃ vacuum/0.5 h + 80℃/4 h + 90℃/3 h + 110℃/2 h + 140℃/5 h. Under the condition, the deposition of powder in potting adhesive is small, and the cured product has the best comprehensive performance.

In this paper, the current fire protection standards of transformer oil for rail transit were introduced in detail. The necessity of synthetic ester as transformer oil for rail transit was described mainly from the aspects of fire safety, environmental protection, moisture resistance, and later oil change maintenance.

Polymer materials such as epoxy resin have hidden dangers of thermal failure and insulation failure during long-term service since its low thermal conductivity. In this study, a high thermal conductive composite insulating material was prepared by filling micron boron nitride and nano alumina with high thermal conductivity and high insulation properties to epoxy resin, and the effect of filling amount and ratio of fillers on the thermal conductivity and insulation properties of composite materials were studied. The results show that when the total filling content is 30% and the mass ratio of micron boron nitride to nano alumina is 3∶1, the thermal conductivity, breakdown time, and imaginary part of complex permittivity (ε″) of the composite materials is 1.182 0 W/(m·K), 31.9 s, and 0.034, respectively, which is improved by 697%, 21.7%, and 406% compared with epoxy resin, respectively. The composite material has good resistance performance under high frequency and high electric field.