On the basis of a new equivalent topology of oil-paper insulation—hybrid model, a variety of model characteristic parameters were extracted to realize the quantitative evaluation of water content in oil-paper insulation. At first, the polarization branch value range of the hybrid model was determined on the basis of parameter coincidence degree by using the measured frequency domain spectrum of oil-paper insulation equipment. And then, the difference between the hybrid model and extended Debye model in reflecting the damp information of oil-paper insulation was compared combined the experimental data and measured data. At last, the effects of water content in oil-paper insulation on the different branch parameters were studied on the basis of hybrid model, and the quantitative relation expression between the parameters and the damp state of oil-paper insulation were established. The results show that when the total number of polarization branch is 5-7, the identification effect of model parameter is better. The hybrid model can express the dielectric response information of oil-paper insulation system more accurately. The extracted model characteristic parameters can realize the quantitative evaluation of water content in insulating paper preliminarily.

In this paper, a series of preparation and modification researches of polyphenylene oxide resin in the field of super high-frequency and low dielectric were reviewed, including the preparation of low molecular weight polyphenylene oxide, chemical structure modification, composite with other resins, organic/inorganic hybrid. Then the existing problems of low dielectric polyphenylene oxide resin were summarized, and its future development trend was prospected.

Firstly, the actual flashover test of large fittings-composite insulator-metal grounding body was carried out in the laboratory environment, the quantitative relationship curve between flashover voltage and space net distance was obtained. Further more, the three-dimensional finite element models of two typical structure of high voltage bushing composite insulators for capacitive core converter transformer and double-layer metal shield through wall were established, and their distribution characteristics of typical voltage and electric field under operating state were obtained, the relationships between local high field strength and corona, flashover phenomena of composite insulators for bushing were analyzed. On the basis of the above theoretical analysis and test data, the size altitude correction and umbrella skirt contour topology optimization of composite insulator for UHV AC/DC bushing were carried out. Finally, all the electric field strength of key parts can meet the control requirements, which proves that the rationality and effectiveness of the design of composite insulator for bushing at UHV level.

In order to improve the capacitance and energy density of polypropylene film, the mixed slurry of high dielectric constant nanoparticles and acrylate binder was used to modify the surface of polypropylene film. By comparing with the properties of polypropylene film before modification, the effects of base film stretching technology, surface modification temperature, and high dielectric nanoparticles size on the properties of the modified polypropylene film were discussed. The results show that after modification, the dielectric constant of polypropylene film increases from 2.20 to 2.89 at 1 kHz, and the energy storage density increases from 2.56 J/cm³ to 3.29 J/cm³ under 500 kV/mm of electric field, which increases by 28.5%. At the same time, the modified polypropylene film maintains stable dielectric properties in the range of 20-120℃, and the variation range of dielectric constant is less than 6.9% under 1 kHz. The solution method used to modify polypropylene film in this study is simple and easy, and is feasible for large-scale preparation, which has a certain reference value for the large-scale preparation of dielectric materials with high energy storage density.

In order to study the influence of winding heat release during actual transformer operation process at extremely low temperature on the breakdown characteristics of transformer oil, the 45^# transformer oil was selected as the research object, and the saturated moisture content of the transformer oil with different temperature under extremely low temperature were tested. A breakdown test platform under low temperature environment was built, and the electric strength of the transformer oil was measured under uniform temperature and gradient temperature conditions. The results show that the relationship between saturated moisture content of the transformer and temperature satisfies Arrhenius equation under low temperature. After fully standing at low temperature, the electric strength of uniform temperature transformer oil increases to a certain extent in low temperature range, and the electric strength at -10℃ increases most obvious where the electric strength is the minimum, which is 51.5% higher than that before standing. The electric strength change curve of gradient temperature transformer oil with temperature is similar to that of the uniform temperature transformer oil, showing a “U” shape distribution as a whole. The minimum electric strength of gradient temperature transformer oil does not decrease compared with that of uniform temperature transformer oil, but slightly increases, and the temperature reaching the electric strength minimum value increases.

In order to study the ageing characteristics of cross-linked polyethylene (XLPE) cable and explore the microscopic factors affecting the dielectric properties of materials, the XLPE cables with different ageing states were conducted isothermal relaxation current (IRC) and partial discharge (PD) tests. A pure polyethylene molecular chain P₁, an aged polyethylene molecular chain P₂ containing hydroxyl groups, and a further thermal-oxidative aged polyethylene molecular chain P₃ containing carboxyl groups were established, and polyethylene molecules with different ageing states were carried out quantum chemical calculation. The results show that with the increase of ageing time, the time constant of depolarization current and ageing factor A increase, and the trap number and energy level depth in insulating medium increase. Besides, there are more partial discharges with higher magnitude occurring in the aged cable. The carbon-oxygen group generated by thermal oxygen ageing in polyethylene molecular chain is an important reason for the increase of trap number and energy level depth, and the type of functional group will affect the distribution of trap energy level directly. Under the effect of electric field, the stability of the aged polyethylene molecular chain becomes worse, the dipole moment is larger, and the charge transfer is more obvious, which make the charges in the aged cable insulation more likely to be trapped and accumulate, resulting in electric field concentration and increase of partial discharge level.

The aromatic ketone polymer 4-allyloxy-2-hydroxybenzophenone (AOHBP) was selected as voltage stabilizer. In order to inhibit the migration and precipitation of voltage stabilizer in polymer, dicumyl peroxide (DCP) was used as initiator to graft AOHBP on PP, and an anti-degradation additive styrene derivative (St) was added to inhibit the material degradation caused by the grafting process of voltage stabilizer. The physical and chemical properties of the modified material were characterized, and the electrical treeing initiation characteristics and DC breakdown characteristics of the modified material were studied. The results show that the AOHBP can graft on the PP matrix by the free radical reaction initiated by DCP, and the St and AOHBP can inhibit the macromolecular degradation of PP during the grafting reaction process synergistically. The grafting modified PP insulating material can inhibit the initiation of electrical tree and improve the DC electric strength significantly.

The fluidity of granular dry unsaturated polyester molding compound was tested at different pressure and temperature by using capillaries of different specifications, and the fluidity and curing behavior during the molding process of the granular dry unsaturated polyester molding compound were studied. The results show that the best conditions for testing the fluidity of dry unsaturated polyester molding compounds by Rasig method are as follows: the test temperature is 160℃, the load pressure is 50 kg, the capillary template pore size is 1.0 mm, and the remaining ingot height is greater than 1.5 mm.

In order to study the design and selection of the composite insulated cross arm for 35 kV transmission line, the feasibility analysis was conducted from material technology, electrical scheme, and structural scheme, the finite element stress analysis was conducted on the tension and compression rods of composite insulated cross arm, and the practical application of the composite insulated cross arm was verified. The results show that the composite insulated cross arm of 35 kV transmission line, which adopts the winding forming E-glass fiber/epoxy resin composite and the single strut and single cable-stayed structure, can meet the requirements of mechanical properties. The composite insulated cross arm has been in good operation since it is applied in the pilot project.

In order to analyze the technological factors affecting the dielectric loss factor of low-voltage forming winding motor stator, the influence rules of four factors including uneven core, oil contamination, insulation moisture, and insulation paint loss on the dielectric loss factor of stator and the corresponding disposal measures were studied. The results show that uneven core, oil contamination, and insulation paint loss lead to the increase of dielectric loss factor of the stator insulation, and the dielectric loss factor of the motor insulation increases significantly when the insulation gets damp. The rise of dielectric loss factor caused by insulation paint loss can be decreased by secondary impregnation.