Two kinds of nano-fillers nano-tiania (TiO₂) and muti-wall carbon nanotubes (MWCNTS) were selected. Sixteen different epoxy nanocomposite dielectrics were prepared by adding two kinds of nanofiller alone or simultaneously to the epoxy resin. The influence of nanoparticles on the surface flashover characteristics of epoxy nanocomposite dielectrics was explored through the volume resistivity test, surface potential decay and vacuum DC surface flashover experiment. The results show that the surface flashover voltage of epoxy nano-composite is related to the mass fraction of filler, and an appropriate amount of filler can enhance the flashover voltage effectively. Comparing with adding TiO₂ (improving 14.49%) and MWCNTS alone (improving 23.11%), adding TiO₂ and MWCNT simultaneously can further improve the surface flashover voltage up to 44.99 kV (improving 36.06%). The surface trap characteristics of the material are calculated by the surface potential decay curve. By analyzing the relationship between deep trap and surface flashover voltage, it is found that the flashover voltage is linearly correlated with the deep trap energy level, and the deeper the trap energy, the higher the flashover voltage. The depth of surface deep trap energy is improved by adding two kinds of nanoparticle into epoxy composites, thus the electron emission and charge transport processes are suppressed, and the surface flashover voltage increases.

In order to study the ablation mechanism of buffer layer of corrugation aluminum (Al) sheath high voltage cross-linked polyethylene (XLPE), firstly, we analyzed a ablation failure of 110 kV XLPE insulated cable, and proposed that the concentrated radial current was the cause of ablation failure. Secondly, a simulation model of the faulty cable was established. The current density and its distribution of the contact part of buffer layer and corrugated Al sheath were simulated, and the simulation results were proved by model experiment and calculation. It was found that the size and distribution of radial current were affected by the embedded depth of Al sheath in the buffer layer and the volume resistivity of the buffer layer. Finally, simulation experiments were designed to prove that the radial current concentrated was one of the causes of buffer layer ablation, and the experimental conditions of the simulated ablation experiment were controlled in the thermostat. The surface morphology of the experimental sample and the ablated Al sheath were compared by optical microscope. The results show that the ablation process in the ablation experiment is the same as that in the actual faulty cable, and with the increase of the current density in buffer layer, the ablation start time decreases. This paper reveals the physical mechanism of radial current concentration in the ablation fault of corrugated Al sheath, which provides guideline for relevant fault diagnosis and protection.

A thermosetting polyester wire enamel with high crosslinking density was prepared by using water-soluble polyester resin as matrix. The adhesion of paint film was regulated by the ratio of hard and soft monomer in polyester resin, the electric strength of paint film was improved by adjusting the branching degree of polyester resin, and the technology of paint film was improved by adding thickening agent. The results show that when the mole fraction of water-soluble functional monomer is 6%, the mole fraction of branched functional monomer is 14%, and the mole ratio of soft and hard chain segments in the remaining monomer is 2∶1, the wire enamel with the water-soluble thermosensitive polyester as matrix has the best comprehensive performance. The optimum mass fraction of curing agent is 3.0% of resin mass. When the mass fraction of thickening agent is 0.4% of the total resin, the elongation at break of the enameled wire is 40%, and the electric strength is 40 kV/mm. The final coating thickness of the enameled wire is 100 μm, its breakdown voltage is 4 kV, and its heat resistance is good, which has potential application value in the new sensor technology and equipment body integrated transformer.

In humid and dirty environment, it is easy for high voltage switchgear to trigger discharge or insulation breakdown fault. To improve the design and operation level of high voltage switchgear, we simulated the electric filed distribution of high voltage switchgear under micro-environment and calculated the minimum discharge distance. Firstly, a multi-physical field finite element simulation model of bus chamber for 40.5 kV high voltage switchgear was established by COMSOL simulation software, and the temperature and humidity distribution in the bus chamber were obtained. The electric field distribution characteristics in the presence or absence of micro-environment were studied by numerical analysis method. Based on the air streamer discharge initiation criterion, the minimum discharge distance in micro-environment was calculated by COMSOL and MATLAB software. Finally, the influence of different insulation partition layout parameters (thickness, location) on the electric field distribution and minimum discharge distance in micro-environment was studied. The results show that the maximum temperature in the bus bar chamber can reach 347.15 K under high temperature and high humidity environment, and the overall temperature presents a gradient distribution of upper and lower. The insulating partition, which is located in the area of low temperature and high humidity, is easy to accumulate wet dirt. In the micro-environment, the electric field at the bus tip and the minimum discharge distance decrease, but the surface electric field increases, and the flashover probability increases.

It is increasingly urgent to the demand of ultra-high voltage direct current (UHVDC) cable equipment because of the implementation of UHVD transmission project. In order to study the structural design of UHVDC cable joints, we start from the influence of nonlinear conductivity characteristics of polymer insulation materials on the insulation electric field distribution of DC cable joints to analyze the effect of modified silicone rubber on the optimal design of the insulation structure of UHVDC cable joints. The results show that the electric field in the reinforced insulation of DC cable joints will reverse polarity with the increases of the cable load current. The nonlinear conductivity of the silicone rubber is greatly enhanced by doping copper calcium titanate nanofibers inorganic filler, the activation energy and electric field strength coefficient of the silicone rubber are improved, and the threshold electric field strength of conductivity entering the nonlinear region is reduced. The distortion of tangential electric field of double-layer dielectric interface and surface electric field of stress cone and high-voltage shielding tube in the UHVDC cable joint are obviously suppressed by the modified silicone rubber reinforced insulation material. The modified silicone rubber, used as the reinforced insulating material for UHVDC cable joints, can make up for the insufficient that the field distortion in the joint cannot be suppressed effectively by adjusting the structural size of cable joints. The research results can effectively solve the electric field control problem in the design of UHVDC cable joints.

In order to study the ablation mechanism of buffer layer in cable, we analyzed the change of contact state between buffer layer and aluminum sheath according to the defect phenomenon, and then a circuit model was established to analyze the defect. According to the model, the induced voltage of insulation shielding layer and the main factors affecting the induced voltage were analyzed. A 15 m defective cable sample was intercepted from the breakdown accident line, and a partial discharge detection experimental platform was built with the defective cable sample. The results show that the induced voltage of insulation shielding layer is directly proportional to the number of defects, the resistivity of composite layer, and the thickness of white powder at the defect, and is inversely proportional to the contact area between buffer layer and aluminum sheath, and the discharge signals inside the defect cable have obvious characteristics of poor contact discharge.

A barium titanate/polyvinylidene fluoride (BT/PVDF) composites was prepared by solution blending method, and the effect of size distribution and content of BT particles on the dielectric properties, electric strength, energy storage properties, and thermal stability of the composites were investigated. The results show that compared with single particle size BT, the synergistic effect of double particle size BT filler makes the composites have more excellent comprehensive properties, and the synergistic effect is the most remarkable when the mass ratio of BT with double size is equal to 1. With the increase of filler content, the dielectric constant and thermal stability of the composites increase, and the dielectric loss factor of the composites maintains at the relative low level. When the mass fraction of BT is 60%, and the mass ratio of BT with double size is 5∶5, the dielectric constant of BT/PVDF composites reaches 46.5 at 100 Hz, which is 5 times bigger than that of pure PVDF; the energy storage density and polarization are 0.18 J/cm³ and 0.011 9 C/m², respectively, which are 176% and 310% higher than those of pure PVDF; the decomposition temperature corresponding to 5% of weight loss reaches 478.4℃, which is 1.3℃ and 30.3℃ higher than that of PVDF composites filled with S-BT and L-BT, respectively.

This paper summarized the global patent layout of corona resistant PI films, the influencing factors of corona resistance for inorganic nano hybrid films, and introduced the application status of corona resistant PI films at liquid nitrogen temperature, as well as the future development of corona resistant PI films.

Partial discharge inception voltage (PDIV) under repetitive pulse voltage is an important parameter to evaluate the insulation performance of low-voltage random-wound inverter-fed motors. Different from the traditional sinusoidal voltage, the rise time and polarity of the impulse are critical parameters to be considered when PDIV test is carried out on the turn to turn insulation of the winding for inverter-fed motor at repetitive impulsive voltages. In this paper, the influence of repetitive impulsive voltage rise time on the PDIV and energy distribution features of turn to turn insulation for inverter-fed motors with three specification were investigated at repetitive impulse voltages with different impulse rise times (50 ns, 75 ns, 100 ns, and 200 ns), and the mechanism of variation of PDIV with different rise times was discussed. The results show that with the decrease of rise time, the PDIV of three motors decreases, and the maximum decline rate reaches 28.1%. The influence of repetitive pulse polarity on the PDIV test results of low-voltage random-wound inverter-fed motor is limited, indicating that both positive and negative can objectively reflect the PDIV performance of motor. With the increase of impulse rise time, the discharge energy in frequency domain moves from high frequency to low frequency. The research results are expected to provide reference for PDIV test of low voltage inverter-fed motor insulation and the revision of related standards.

In order to verify the applicability of DGA fault diagnosis methods in oil-filled submarine cable, we chose domestic dodecylbenzene (DDB) insulating oil as research object. First, the decomposition temperature of DDB insulating oil was determined by thermogravimetric test under different heating rates. Subsequently, a test system was built to carry out thermal fault simulation tests of DDB pure oil, oil-paper, and 25^# mineral oil at 150, 250, and 350℃. After test, the percentage of five characteristic gases (H₂, CH₄, C₂H₆, C₂H₄, C₂H₂) dissolved in the fault oils was measured to study the gas production law of DDB insulating oil under thermal fault. Finally, existing DGA diagnostic methods (classic Duval triangle, quadrilateral graphic method) were selected to analyze the gas data. The results show that the proportion of C₂H₄ dissolved in DDB insulating oil under thermal fault increase significantly with the increase of fault temperature, and the proportion of C₂H₄ in mineral oil is at a low level in the whole temperature range. In the thermal fault diagnosis, the classic Duval triangle and quadrilateral graphical method can detect thermal faults by the dissolved gas in DDB insulating oil, but the temperature range of thermal fault cannot be determined accurately, and the fault boundary need to be further modified.