The liquid crystal epoxy monomer was cured to obtain liquid crystal epoxy resin prepolymer, and liquid crystal epoxy resin fiber films with different fiber diameters were obtained by electrospinning technique. The birefringence of the samples was observed by polarizing microscopy and removable hot stage, and the mechanical properties, dielectric properties, and insulation properties of the liquid crystal epoxy resin fiber films with different fiber diameters were systematically evaluated. The results show that the liquid crystal epoxy resin prepared by electrospinning method can form and maintain an ordered liquid crystal phase. The finer the fiber diameter, the higher the degree of orientation arrangement, and when the fiber diameter is 280 nm, the tensile strength (7.53 MPa) of the liquid crystal epoxy resin fiber film is the largest. Under the test frequency ranging from 10^-1 Hz to 10⁶ Hz, the dielectric constant of the liquid crystal epoxy resin reaches to the highest value of 2.34, and the dissipation factor is only 0.002 at industrial frequency. In addition, the liquid crystal epoxy resin fiber film has high resistivity, and when the fiber diameter is 280 nm, the volume resistivity of the liquid crystal epoxy resin fiber film can reach to 5.49×10¹⁵ Ω·cm.

In order to research the insulation ageing characteristics of cross-linked polyethylene (XLPE) cables, it is necessary to perform ageing tests under laboratory conditions. In this paper, the current research progress on insulation ageing tests and detection techniques of XLPE cables was reviewed. Firstly, the common ageing types and phenomena of XLPE cables were introduced, and the current research results on the growth mechanism and influencing factors of water tree ageing and electrical tree ageing were elaborated. Secondly, the accelerated ageing test methods for XLPE cables under laboratory conditions and their effect on cables were introduced. Then, the current detection methods of cable insulation ageing were briefly classified, the principle, applicable conditions, and advantages and disadvantages of each methods and the characteristics and application method of each insulation detection stage were introduced. Finally, the problems related to cable insulation ageing and their future research directions were discussed.

Considering the equivalence between sequential stress test and constant stress test, we proposed a mixed stress test method that the sample was applied voltage in the order of sequential advance stress-constant stress-sequential advance stress, and then the voltage withstand index n of XLPE flake sample was evaluated by this method combined with Weibull statistical analysis. The results show that the voltage tolerance index n calculated by the mixed stress test is 16.11, the deviation between it and the n evaluated by the constant stress test is 5.36%, and its total evaluation time is shortened by 98.04% than that of the constant stress test, which proves that this method can evaluate the voltage withstand index of XLPE insulation effectively.

In order to study the high temperature resistance of hydrophobic properties of PRTV coating and the difference of thermal ageing characteristics between epoxy resin coated with PRTV coating (EPTL) and epoxy resin uncoated with PRTV coating (EP). The EPTL and EP were conducted thermal ageing tests at 80, 100, 120℃, and their dielectric properties, internal microstructure, thermal stability, and hydrophobic properties were compared and analyzed. The results show that after the thermal ageing tests under different temperature, the dielectric properties and thermal stability of EPTL are better than that of EP, and the internal microstructure is more complete. Although EPTL still shows strong hydrophobic properties after ageing, the contact angle decreases rapidly, which indicates that the hydrophobicity of PRTV coating is affected by high temperature greatly.

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.

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.

A 500 kV decay-like composite insulator was conducted infrared temperature rise tests under dry conditions, 55%, 75%, 95% of ambient humidity and 3, 5, 7 m of observation distances to study the temperature rise characteristics of the decay-like composite insulator under different humidity and observation distance. The results show that the temperature rise of the decay-like composite insulator increases with the increase of ambient humidity, its temperature rise in 95% of humidity environment increase by 22%-40% compared with that under dry environment. When the humidity is constant, the temperature rise decreases with the increase of observation distance. The deteriorating section length of the core rod can be judged by the temperature rise distribution curve characteristics on the axis of decay-like composite insulator, which can realize the non-destructive detection of the deteriorating section length of decay-like insulator.

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.

With the development of power capacitors towards lightweight and miniaturization, dielectric materials with high energy storage density have broad application prospects in the field of capacitors, among them, nanocomposite dielectrics with core-shell structure have attracted extensive attention due to their excellent energy storage properties. In this paper, the latest progress of nanocomposite dielectrics with core-shell structure were introduced, the preparation methods of nanofillers with core-shell structure were introduced, including organic surface modification and inorganic shell covering. Then the effect mechanism of nanofillers with core-shell structure on the electric strength, dielectric constant, and dielectric loss of nanocomposite dielectrics were discussed, and the construction strategies of nanocomposite dielectrics with core-shell structure were provided. At last, the existing problems in the design of high energy storage density nanocomposite dielectrics with core-shell structure were summarized, and their future development direction was prospected.

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.