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.

Two kinds of modified magnesium hydroxide (MH) were used as flame retardant, and then compounded with low density polyethylene (LDPE) to prepare LDPE/MH flame retardant materials. The effects of the flame retardants on the mechanical properties, flame retardant properties, thermal stability, and electrical properties of the materials were studied. The results show that the flame retardant properties of the materials increase significantly after adding the modified magnesium hydroxide flame retardant, but the mechanical properties, thermal stability, and electrical properties decrease. The flame retardant of the LDPE with amino silane coupling agent modified magnesium hydroxide is better than that of the LDPE with alkyl silane coupling agent modified magnesium hydroxide, but its adverse effects on mechanical properties and electrical properties of materials are more obvious. When the addition amount of alkyl silane coupling agent modified magnesium hydroxide is 70 phr, the comprehensive properties of the material are better.

The thermal conductivity of insulating varnish could be improved by adding inorganic oxide thermal conductive material into the epoxy modified unsaturated polyester resin. The effect of particle size and surface modification of fillers on the sedimentation of insulating varnish and effect of different filler content on the thermal conductivity and viscosity of insulating varnish were studied. A high thermal conductive and solvent-free insulating varnish was prepared, and its performance was characterized. The results show that the surface modification of filler could reduce its sedimentation rate. When the filler content is 40%, the viscosity of insulating varnish is 72 s, the thermal conductivity reaches 0.46 W/(m·K), and the insulating varnish exhibit no sedimentation at 40℃ after 6 days, which indicates that it has practical application value.

The effects of electric field and temperature on the diffusion behavior of water molecules in nano-SiO₂ modified insulating oil were studied by molecular simulation technology. The results show that the water molecules are polarized under electric field, and the water molecules would change from an original disordered arrangement to an ordered arrangement along the direction of electric field. Therefore, under the action of electric field, the Brownian motion of water molecules weakens, and the diffusion ability of water molecules in oil decreases. The electrostatic force between water molecules and oil medium was enhanced by electric field, which is 2‒3 times bigger than that without electric field. This is also the main reason for the increase of interaction energy between water molecules and oil medium under electric field. In addition, under the action of electric field, the free volume fraction of the model decreases, and the effect of temperature on the hydrogen bond between O and H atoms in the model weakens.

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.

DGEBA/OSC cross-linked epoxy resin blend systems with different proportions were constructed by molecular dynamics (MD) simulation using methyl tetrahydrophthalic anhydride (MTHPA) as curing agent, and the blend system samples were prepared. The thermodynamic properties of the blending systems were studied by simulation and experiment. The simulation and test results show that with the increase of the OSC proportion, the glass transition temperature (T_g) of the blend systems increases, when the molar ratio of DGEBA to OSC is 6∶4, the T_g increases by 30.7 K. The elastic modulus and strength of the systems increase at first and then decrease, and reach the optimum at 8∶2 of molar ratio. The addition of OSC can reduce the fractional free volume (FFV) and mean square displacement (MSD) of the systems, and weak the molecular segment movement ability. The calculation results of synergy rotational energy barrier and cohesive energy density (CED) show that the blend system with stronger molecular segment rigidity and larger interaction force between segments has better thermodynamic properties.

The high thermal conductive insulation structure applied in H-class AC high voltage motor was studied. The coil samples with the insulation structure were conducted turn-to-turn impulse, withstand voltage to ground, dielectric loss factor, breakdown voltage, voltage durability (electrical ageing), thermal evaluation and classification (thermal ageing) experiments, and the thermal conductivity of several dry mica tapes were tested and analysed. The results show that the application of dry mica tape with high thermal conductivity could improve the thermal conductivity of insulation structure for motor, and the temperature rise reduces effectively. The insulation structure also show good electrical performance, and the temperature index reaches 181℃, which can meet the requirements of the insulation structure for H-class motor.

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.

The increasingly developed microelectronic devices have put forward higher requirements on thermal conductive and electrical insulating thermal interface materials, and the silicone rubber composites with high thermal conductivity and electrical insulating can be prepared through construction of micro-nano hybrid heat conduction network. First, a nano-alumina coated graphene oxide was prepared by a simple and green self-assembly strategy, and it was reduced into TRGO@Al₂O₃ nano-hybrid filler by high temperature treatment. Then it was mixed with micron alumina and filled into liquid silicone rubber. The influence of different nano alumina coated amounts on the thermal conductivity and volume resistance of the system was studied by adjusting the ratio of nano alumina to graphene oxide. The synergistic thermal conductive effect of the micro-nano hybrid system was studied by controlling the ratio of nano-hybrid filler to micron alumina. The results show that when the 3% of TRGO@Al₂O₃ and 54% of micron alumina are compounded, the thermal conductivity of the composite reaches about 2.5 W/(m·K), and the volume resistance is greater than or equal to 10⁹ Ω·cm.

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.