The effect of thermal oxygen ageing on the properties of irradiated ethylene propylene diene rubber (EPDM) materials were analyzed, and its theoretical service life was evaluated by analyzing the change rule of compression permanent deformation rate with time. The results show that with the increase of ageing time and ageing temperature, the irradiated EPDM is aged more and more serious, the carbonyl content becomes higher and higher, and the compression set and compression stress relaxation become greater and greater. The SEM results show that the EPDM degrade seriously during ageing process. According to Arrhenius equation, the theoretical life of the irradiated EPDM is 7.58 years at 50℃.

On the basis of laser ultrasonic technology, a peak reconstruction algorithm of surface wave was studied, and an experimental platform of two-dimensional laser excitation scanning laser ultrasonic detection for basin insulators was built. Then the artificial bubble, impurity, and crack defects were detected and studied, and the basin insulator with crack fault in practical field application was carried out off-line detection. The results show that the reconstructed peak image based on laser ultrasonic peak reconstruction algorithm can better reflect the defect information of basin insulator in scanning interval, which proves that this method can realize the off-line detection of surface crack defect on the basin insulator.

Current-carrying capacity is an important indicator of cable transmission capacity, which directly affects the operation reliability and economy of HVDC cables. According to the electric field distribution characteristics in the insulation layer of DC cable, an analytical calculation method of the electric field distribution inside and outside the insulation layer based on the equivalent conductivity was proposed. Taking a ±535 kV XLPE insulated DC cable as example, considering the highest operating temperature of cable conductor and the maximum allowable temperature difference of insulation layer, we obtained the load control domains of the HVDC cable under different operating conditions. The results show that the current-carrying capacity and application characteristics of HVDC cables can be analyzed by the electric thermal field decoupling method effectively, and the maximum temperature difference of insulation layer is the core factor limiting the current-carrying capacity of DC cable below critical ambient temperature. Under the critical ambient temperature, raising the highest operating temperature of conductor has limited influence on the current-carrying capacity, while optimizing the electrical resistance of insulating materials and cable structure is the key to improving the current-carrying capacity.

Firstly, a corresponding simulation model was built on the basis of terminal structure of 220 kV high-voltage dry cable, and combined with the nonlinear conductivity equation of insulating materials, the electric field distribution and temperature distribution in the terminal with different reinforced insulating materials, ambient temperature, and applied voltage were studied. And then, the electric field distributions of the terminal with defects such as misplacement of stress cone installation, surface bulge, and bubbles in the reinforced insulation were compared and analyzed. Finally, the corner shape of stress cone and the distance between stress cone edge and reinforced insulation were optimized, the electric field distribution of the terminal after optimization was analyzed, and the optimal distance between stress cone edge and reinforced insulation was proposed. The results show that the nonlinear silicone rubber insulating material can well homogenize the electric field. The change of external ambient temperature will decrease the temperature difference between the internal core and the external umbrella skirt, and the maximum field strength in terminal increases significantly with the increase of ambient temperature. The stress cone installation dislocation makes the field strength at the three-phase junction increase sharply. The bulge on stress cone surface makes the local field strength in terminal increase sharply. When there are bubbles in reinforced insulation, the bubble size has little effect on the maximum field strength in the cable terminal. By changing the corner shape of stress cone into a circular arc shape, the field strength at the corner decreases by 75.26%. By increasing the distance between stress cone edge and reinforced insulation to 5 mm appropriately, the field strength at the stress cone corner decreases.

Aimed at a new type of three-element mixed insulating oil, we developed a mixed insulating oil transformer with high overload capacity. On the basis of the analysis on the heat resistance grade and temperature rise limit of the mixed insulating oil transformer and mineral insulating oil transformer, the temperature rise of insulating oil distribution transformer with different overload capacity was compared combined with the relevant calculation and test detection of the model machine. Some structural optimization suggestions of mixed insulating oil distribution transformer were proposed and the cost was compared. The results show that the overload capacity of oil-immersed distribution transformer can increase from 1.5 times to 1.75 times by using the hybrid insulation system composed of a new type of high temperature resistant ternary mixed insulating oil and DPE insulating paper or Nomex T910 insulating paper, and the corresponding cost increases less than 8%, which has strong practicability and economy.

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.

The broadband dielectric response of oil-paper insulation was studied, and broadband dielectric response tests were carried out on laboratory samples of oil-paper insulation with different moisture contents. According to the relaxation polarization part of dielectric spectrum, the spectral parameters characterizing the moisture degree were extracted, and their relationship with the moisture content in the oil-paper insulation was analyzed. Further moisture tests for the oil-immersed bushing scaled-down model were designed, and the application of the spectral parameters in the moisture diagnosis of bushing was discussed. The results show that the low-frequency polarization process in the relaxation polarization spectrum is more sensitive to the moisture content, and its loss peak value can be used as a characteristic parameter to characterize the moisture content; under different moisture types of the bushing, the change patterns of the loss peaks and characteristic frequencies of the low-frequency and high-frequency relaxation polarization are different, which can be used as a preliminary criterion for the moisture type of the bushing.

A novel film capacitor was prepared by using a mass-produced surface modified high dielectric polypropylene film, and the power density, energy storage properties, capacity retention ratio, and the cycle life under large current of the capacitors were studied. The results show that the maximum energy storage density of the new capacitors with the surface modification polypropylene film can reach to 3.2 J/cm³, and the capacitor shows excellent comprehensive performances.

Three typical imported PP resins with a large market share for capacitor application were chosen, and their molecule structure, aggregation structure, and electrical properties were systematically measured. The influence law of molecular weight and distribution on the crystallization properties, as well as the action mechanism of crystallization properties on dielectric and breakdown properties was investigated, and in consequence the correlations between microstructure and macroscopic electrical properties was built. The results show that optimizing the molecular weight and distribution avoiding too large and narrow can contribute to regular and compact alinement and stacking of molecules, and then the orientation of dipole and transportation of electrons can be inhibited, resulting in the decrease of dielectric loss and increase of breakdown strength.

Crosslinked polyethylene/organic montmorillonite (XLPE/OMMT) nanocomposites were prepared by melting blending method. The performance of samples before and after thermal ageing were characterized by small angle X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and mechanical properties test. The results show that with the mass fraction of 0.5%, OMMT can be well dispersed in the matrix before ageing. However, OMMT agglomerates when the filler doping amount increases. There are only a few chemical bonds between OMMT and XLPE matrix, they mainly coexist in the form of physical entanglement. The crystallinity of nanocomposites decreases due to the space steric effect of OMMT lamella. After ageing, the layer spacing of XLPE/OMMT-0.5% samples decreases and the crystallinity increases. With the increase of OMMT doping amount, the interlayer spacing of OMMT increases due to the breakdown of XLPE molecular chain and the thermal rearrangement of OMMT in matrix. Due to thermal ageing, the completeness of crystal structure of nanocomposites gets worse, the crystal size distribution becomes wider, and the crystallinity decreases significantly. The molecular chain structure of nanocomposites is seriously damaged by thermal oxidation and thermal cracking. The mechanical property of XLPE/OMMT-0.5% decreases slightly after ageing, and when the content of OMMT exceeds 0.5%, the mechanical properties of nanocomposites decrease seriously. And the samples become brittle and hard.