Nuclear grade medium voltage cables were conducted thermal-water tree and irradiation-water tree ageing tests. The nuclear grade medium voltage cables with different ageing time were tested by PDC method to obtain the conductivity under different voltages, and the nonlinear coefficients under different ageing conditions were obtained through the conductivity. The results show that with the increase of ageing time, the nonlinear coefficients of the cable samples under two ageing conditions increase gradually. Under the condition of heat-water tree combined ageing, with the increase of ageing time, the absorption peak intensity of O-H bond increases, indicating that the cable samples are water tree aged more seriously. In the irradiation-water tree ageing test, the absorption peak intensity of O-H bond increases slightly, indicating that the ageing degree of water tree increases. At the same time, although the characteristic peak of O-H bond appears near 1 640 cm^-1 in the infrared spectra of water tree aged cable sample, the peak value changes little with the increase of irradiation dose. Therefore, the results of O-H bond absorption peak in infrared spectrum test can not well reflect the radiation ageing state of cable, but can only reflect the ageing state of water tree.

The dielectric constant and dielectric loss of composite insulating paper can be reduced by doping different content of aramid 1313 (PMTA) in the natural cellulose pulp, but the mechanical properties of composite insulating paper are greatly reduced due to the poor combining ability of two fibers. In order to solve this problem, we studied the improvement effect of low-temperature plasma treatment on the binding capacity of two kinds of cellulose emphatically, and tested and analyzed the properties of the prepared composite insulating paper. The results show that the low-temperature plasma treatment can effectively improve the binding force between the two kinds of fibers, so as to make up for the loss of mechanical properties, and it has little influence on the dielectric and breakdown characteristics of the composite insulating paper. The results of SEM and XPS show that the surface of PMTA fiber after low temperature plasma treatment become rough, the polarity functional group increases, the binding force with cellulose matrix increases, and the voids of composite insulating paper sample decreases significantly. The power frequency relative permittivity of the composite insulating paper prepared by doping low temperature plasma treated PMTA in natural cellulose pulp is reduced, while the AC/DC electric strength and volume resistivity remain unchanged, and the tensile strength and elongation at break are compensated to the maximum.

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 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 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.

A derived diamine monomer of 1,3-bis(4-aminobenzoyoloxymethyl)-1,2,2-trimethylcyclopentane (BABMT) was synthesized from a biomass small molecule natural-(D)-camphor. It was polymerized with aromatic structure dianhydrides (BPDA and ODPA) to prepare semi-alicyclic structure polyimide (PI) films, respectively, and their thermal properties, mechanical properties, optical properties, and solubility were compared with that of the wholly aromatic structure PI films prepared by alicyclic structure diamine (DMB) polymerizing with alicyclic structure dianhydrides (BPDA and ODPA), respectively. The results show that the semi-alicyclic structure PI films have good thermal properties, the glass transition temperature (T_g) is 281℃ and 236℃, respectively, and the 5% weight loss temperatures (T_d5) is not lower than 390℃. At the same time, the semi-alicyclic structure PI films retain good mechanical properties, the tensile modulus is 2.13 GPa and 2.41 GPa, respectively, the tensile strength is 109 MPa and 97.9 MPa, respectively, and the elongation at break is 7.7% and 11%, respectively. Compared with the wholly aromatic structure PI films, the semi-alicyclic structure PI films show better transparency with the transmittance at 500 nm (T₅₀₀) over 78%, and better solubility in common organic solvents. Wide-angle X-ray diffraction results show that all the semi-alicyclic structure PI films present amorphous structure, and their interchain spacing (d) are larger than that of the wholly aromatic PI films.

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 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.

The partial discharge inception voltage (PDIV) of the turn-to-turn insulation for low-voltage random-wound inverter-fed motor changes with the rise time of pulse voltage, resulting in that it is difficult to find the vulnerable spot of the insulation system when the rise time changes. Therefore, considering the rise time of pulse width modulation, we proposed a three-curve method to determine the insulation vulnerable spot of inverter-fed motors by combining the PDIV test technology under repetitive pulse and sinusoidal voltages. At first, the minimum PDIV distributions of main insulation and phase-to-phase insulation were obtained by testing their PDIV under the sinusoidal voltage. Then, the turn-to-turn insulation of inverter-fed motor was conducted PDIV tests using the repetitive pulse voltage with 50-200 ns of rising time, and the fitting curves of PDIV with rising time were obtained. At last, according to the three-curve diagrams, considering the rise time of motor, the vulnerable spot of insulation system was determined, and the feasibility of three-curve method was verified by breakdown experiment. The results show that the insulation vulnerable spot of low-voltage random-wound inverter-fed motor can be judged by the three-curve method, and the feasibility of the three-curve method is verified by breakdown test.

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.