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 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.

In order to deeply grasp the breakdown characteristics of AC 500 kV cross-linked polyethylene (XLPE) submarine cable insulation materials under electrical-thermal stress and establish an electrical-thermal combined lifetime model, we conducted electrical-thermal breakdown experiments on the XLPE material at 25, 40, 55, 70℃ under step stress firstly. The AC electric strength and voltage duration time were analyzed by Weibull distribution to obtain the equivalent AC electric strength and voltage duration time at different temperatures. Then the FALLOU, SIMONI, CRINE models were established by multiple linear regression method, and their error was analyzed. Finally, an E-T lifetime model for the AC 500 kV XLPE material was constructed. The results show that at the same temperature, the equivalent electric strength decreases with the increase of voltage duration time of each voltage stage. At the same voltage duration time of each stage, with the increase of temperature, the equivalent AC electric strength and voltage duration time both firstly increase and then decrease. The analysis on the electrical-thermal lifetime models indicate that the fitting error of FALLOU, SIMONI, CRINE models is large, and their fitting goodness do not meet the accuracy requirements. An improved electric-thermal combined ageing lifetime model is obtained by using stepwise regression to calculate the significance and correlation between electric-thermal variables and lifetime, and the error analysis show that it has better fitting accuracy.

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.

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.

A polyacrylonitrile (PAN)/styrene-isoprene-styrene (SIS) composite fiber membrane was prepared by electrospinning method. The effects of different PAN/SIS ratios on its porosity, liquid absorption, thermal stability, mechanical properties were studied. The results show that when the ratio of PAN to SIS is 8∶2, the SIS/PAN composite membrane fiber prepared has the most cross-linked structures, uniform size, and the best mechanical properties. The tensile strength is 20.29 MPa, the porosity and absorption rate reach 47.8% and 310.7%, respectively, and the ionic conductivity is 2.03×10^-4 mS/cm. Under the condition of 0.2 C multiplier, the initial discharge specific capacity of Li-ion battery assembled by the composite fiber membrane is 146.4 mAh/g, the discharge specific capacity fluctuates little after 50 cycles, and the capacity retention rate is as high as 98.02%, showing good cycle stability.

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 .

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.

Spherical alumina was introduced in drawing and filtering process of graphene nanosheets to build a binary porous structure of “pea-pod-like” alumina-graphene, and an alumina-graphene binary structure reinforced epoxy resin composite was prepared. Its thermal conductivity was tested, and the mechanism of “pea-pod-like” alumina-graphene binary structure enhancing the thermal conductivity of epoxy resin was analyzed. The results show that the horizontal arranged graphene generates partial orientation transformation under the action of spherical alumina, showing a “pea-pod-like” structure, in which graphene provides an efficient heat transfer channel for epoxy composites in plane and out of plane directions and greatly enhances the thermal conductivity of epoxy composites. The thermal conductivity of “pea-pod-like” binary alumina-graphene reinforced epoxy composite is up to 13.3 W/(m·K) and 33.4 W/(m·K) in plane and out of plane directions, respectively with 12.1% of graphene and 42.4% of alumina loading. The “pea-pod-like” alumina-graphene binary structure has a significant effect in improving the thermal conductivity of epoxy resin, which has potential application prospects in the field of electrical packaging.