According to the sand parameters around the transmission line corridors in Tibet, Xinjiang, Qinghai and other high incidence of sandstorms regions and the relevant data of dust weather, the wind speed, particle size, concentration, charge/mass ratio and other specific parameters for sand simulation were determined, and a testing apparatus was built. The effect of simulated sand conditions on the power frequency discharge voltage of external insulation in the gap was tested by using this device at an altitude of 2 200 m. The results show that the simulated sand dust environment will decrease the power frequency discharge voltage of the short gap below 0.2 m, but will not reduce the power frequency discharge voltage of the long air gap above 0.2 m, and the charged dust in the air itself is not the cause of the gap trip discharge.

According to the characteristics of series resonance circuit, a new model for calculating the dielectric dissipation factor of high-voltage power cable was established, and a new dielectric loss factor calculating formula derived from the differential power of the series resonance circuit was proposed. On the basis of test model, the dielectric dissipation factor of XLPE power cable was calculated by the step-up or step-down process of the series resonance to solve the problem of dielectric dissipation measuring of high voltage and large capacity cable. The results show that the simulation calculating values of circuit parameters and field test results match with the actual values. Compared with conventional electric bridge method, the test method for calculating dielectric dissipation factor based on the resonance characteristic is more accurate to a certain extent. This provides a reference for testing the dielectric dissipation factor of high voltage and high capacity power cable.

The effects of doping micro-SiO₂ on the electrical tree resistance, thermal stability, thermal conductivity, and trap characteristics of epoxy resin under repetitive frequency bipolar square wave voltage were investigated. The results show that the electrical tree breakdown time of epoxy resin is prolonged by doping micro-SiO₂, and the prolong effect is the most obvious at 10 kHz, the electrical tree breakdown time is prolonged from 6 min to 44 min. Doping micro-SiO₂ can also increase the thermal conductivity of the epoxy resin and reduce the degradation of epoxy molecular chain at high temperature. The micro-SiO₂ filler can introduce more deep level traps, hinder the development of electrical tree channels, extend and even block the development path of electrical tree, which decreases the damage degree of molecular chain. Therefore, doping micro-SiO₂ can effectively improve the electrical tree resistance of epoxy resin under repetitive frequency bipolar square wave voltage.

A silicon-containing propargyl ether of bisphenol A (PSPE-A) was synthesized by the polycondensation of bisphenol A dipropargyl ether and chlorosilane, and a diacetylenic benzene end-capped silicon-containing propargyl ether of bisphenol A (DPSPE-A) was synthesized by two step method. Then the bis(triphenylphosphine) nickel dicarbonyl, octacarbonyl dicobalt, and bis(cyclopentadiene) cobalt were used to catalyze the curing of the PSPE-A and DPSPE-A resins, respectively, and a carbon fabric (T300CF) reinforced silicon-containing propargyl ether of bisphenol A resins was prepared. The thermal curing and thermal properties of PSPE-A and DPSPE-A were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic thermomechanical analysis (DMA), and the mechanical properties of the PSPE-A based composites were studied. The results show that end capping with diethynyl benzene can increase the thermal properties of PSPE-A resin. The three catalysts can all decrease the curing temperature of PSPE-A resin, and the initial curing temperature of PSAPE-A and DPSPE-A decreases by about 130℃ and 60℃ after using bis(cyclopentadiene) cobalt, respectively. The flexural strength of the cured PSPE-A and DPSPE-A is 35.8 MPa and 27.8 MPa, respectively. The flexural strength of T300 carbon fabric reinforced PSPE-A and DPSPE-A composites is 458.2 MPa and 287.6 MPa, respectively.

In order to improve the dispersion of carbon nanotubes (CNTs) in epoxy resin (EP) nanocomposites and the interface interaction between them, so as to prepare EP nanocomposites with excellent comprehensive properties, polyvinyl pyrrolidone (PVP) molecular chains were grafted to the surface of CNTs by covalent bonding under the action of Fenton reagent, and the dispersion of modified CNTs in ethanol and acetone was studied. Then the modified CNTs were compounded with EP to prepare nanocomposites, and their comprehensive properties were studied. The results show that the traditional physical coating modification of CNTs by PVP can be changed into chemical modification with covalent bond through the HO∙ with strong oxidation decomposed by Fenton reagent, and hydroxylation modification can be realized, which improves the grafting rate of PVP. After modification, the CNTs have good dispersion in ethanol and acetone. There is a strong interface interaction between the modified CNTs and EP, which can improve the mechanical properties of EP obviously. When the mass fraction of modified CNTs is 0.25%, the impact strength and flexural strength of the nanocomposites increase by 58.6% and 5.2%, respectively.

A medium-density aramid pressboard was prepared by using meta-aramid chopped fiber and precipitated fiber as raw materials, the effects of chopped fiber length, grammage of single pulp layer, and moisture content of paper billet on the properties of the aramid pressboard were studied. The conventional properties, compatibility, and processing performance of the aramid pressboard were studied. The results show that when the chopped fiber length is 7 mm, the grammage of single pulp layer is 64 g/m², and the moisture content of paper billet is 63%, the aramid pressboard has excellent electrical and mechanical properties, good compatibility with synthetic ester transformer oil and silicone transformer oil, and good processing performance, which meets the application requirements of traction transformer and offshore wind power oil-immersed transformer.

The surface of meta-aramid paper was coated with poly(m-phthaloyl-m-phenylenediamine) (PMIA) slurry with different solid contents, and the coated meta-aramid paper was dried. The morphology, mechanical properties, dielectric properties, and electric strength of the modified meta-aramid paper were characterized by cold field emission scanning electron microscope, universal testing machine, broadband dielectric impedance spectrometer, and electric strength testing instrument. The results show that the PMIA slurry can change the structure of aramid paper and decrease the internal void of aramid paper. When the solid content of PMIA slurry is 10%, the transverse and longitudinal tensile strength of meta-aramid paper increases to 51.3 MPa and 94.4 MPa, respectively, the dielectric constant of meta-aramid paper is 2.07, and the electric strength of meta-aramid paper increases to 29.83 kV/mm. The mechanical properties and electric strength of the meta-aramid paper coated with PMIA slurry are better than those of original aramid paper. After treated at 180℃, the mechanical properties and electric strength of the modified meta-aramid paper are still better than those of original meta aramid paper, which can meet the applications of aramid paper in higher electric field environment and further broaden the applications field of aramid paper.

A series of polypropylene/ethylene propylene copolymer (PP/EPC) cable materials were prepared by blending polypropylene (PP) with two kinds of ethylene propylene copolymer (EPC) with different ethylene content. The effects of EPC types and contents on the mechanical, thermal, and electrical properties of PP were investigated. The results show that the addition of EPC improves the toughness of PP significantly on the basis of maintaining the original excellent thermal and electrical properties of PP, and the toughening effect is more obvious by increasing the amount of EPC and the ethylene content in EPC.

In order to compare the discharge characteristics difference of metal particles and bubbles in flowing transformer oil, the flowing oils containing impurities were conducted partial discharge (PD) and breakdown experiments on a simulating experiment discharge platform. The waveforms of discharge signals were compared, and the phase resolved partial discharge (PRPD) maps were established. The results show that there are significant differences between the discharge characteristics of two defects in flowing oil. The metal particle PD can excite ultra high frequency signals, while the bubble PD can only excite very high frequency signals. The metal particle PD covers all the power frequency cycle, and the bubble PD distributes in the power frequency negative half cycle (236°-305°) mainly. Compared with metal particles, the effect of bubbles on the breakdown voltage of transformer oil is more serious.

In order to study the thermal conductivity of high thermal conductive (HTC) mica tape, the micro structure of different high thermal conductive VPI dry mica tapes were analyzed, and a thermal conductivity test method of HTC dry mica tape was proposed. A comprehensive evaluation method of thermal conductivity was discussed. The results show that under the existing VPI system, the thermal conductivity of the main insulation with high thermal conductive mica tape increase by up to 45% compared with the main insulation with conventional mica tape. Using the comprehensive thermal conductivity λ_s to measure the contribution of high thermal conductive mica tape is more objective and comprehensive, and the comprehensive thermal conductivity of the main insulation with high thermal conductive mica tape increase by up to 33% compared with the main insulation with conventional mica tape.