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.

To research the strain characteristic and its measurement method of encapsulation insulation for dry-type air-core reactor, the methods of making test model, embedding sensor and strain gauge, and calculating strain were studied. A test model was made and a test system was built, and the internal strain of encapsulation was studied during the process of reducing temperature and applying current at different low temperatures. The results show that the circumferential thermal expansion coefficient of the encapsulation insulation is less than the axial thermal expansion coefficient and there is anisotropy, which makes the circumferential strain larger than the axial strain. During the process of reducing temperature, negative strain is produced by circumferential shrinkage of the encapsulation insulation, which decreases gradually with the temperature decreasing, the decline rate gradually slows down in the same cabin temperature, and the value increases significantly with the increase of temperature decline amplitude in different cabin temperatures. The axial strain is positive when the cabin temperature is higher, which gradually changes to a negative value with the temperature decreasing, and the change law also changes from gradually increasing to gradually decreasing with the temperature decreasing. During the process of reducing temperature, the circumferential and axial strains have negative jumps many times, resulting in shrinkage micro-cracks. The strain change during process of applying current is contrast to the process of reducing temperature, with the increase of temperature, the circumferential strain increases gradually, the axial strain decreases rapidly, and neither strain jumps. By calculating the maximum thermal stress, it is further verified that the circumferential compression stress is larger than the compression strength of the epoxy glass fiber, resulting in the damage of encapsulated insulation.

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.

Aimed at the early fault of 10 kV high power traction motor end winding insulation layer, the failure mechanism of insulation layer crack damage under complex electromagnetic and mechanical forces was analyzed on the basis of fracture mechanics theory. A three-dimensional analysis model was established by using the finite element method, and the stress-strain states of the insulating layer crack at different positions were calculated numerically by piecewise loading electromagnetic force. At the same time, the stress intensity factor was introduced to evaluate the degree of crack damage expansion. The results show that compared with the insulating layer crack damage at the nose end, the crack expansion speed at the rod joint is faster and the fracture degree is greater. The initial damage state of the crack also has an important influence on the fracture and expansion degree, and the transverse crack is easier to expand.

The key power equipment with the oil-pressboard insulation winding structure is prone to appear the problem of acetylene content exceeding the standard when putting into operation, and then partial discharge and arcing phenomena are produced. Therefore, the point discharge and arcing characteristics of oil-pressboard insulation were studied under switching impulse voltage and superimposing power frequency electrical stress. The discharge and arcing characteristics of different point defects were compared and analyzed, and the influence of the superimposed phase of impulse voltage and power frequency voltage was discussed. The results show that the arcing process of the defect model containing pressboard after breakdown can divide into high-frequency re-arcing stage, stable arcing stage, and re-arcing stage before the voltage restored. Among them, the high-frequency re-arcing stage has higher arcing frequency and lower recovery voltage. Under the switching impulse voltage, the pure oil gap defect model shows multiple breakdown, and the oil-pressboard composite insulation defect model shows that the pressboard breakdown directly and the oil pressboard breakdown successively, and the defect model type affects the discharge characteristics and arcing rule. The superposition phase affects the discharge characteristics and arcing law by affecting the electrical stress magnitude.

A resin paste was prepared from vinyl resin, low shrinkage agent, powder, initiator, and polymerization inhibitor. The resin paste was used to impregnate continuous glass felt, then a polyester glass fiber felt board prepreg was obtained after curing, and a polyester glass fiber felt board was prepared by mould pressing and hot pressing. The preparation of resin, the selection of initiator system, and the pressing molding process were studied. The results show that with the increase of the thickness of polyester glass fiber felt board, it is more difficult to mold, and there are more internal defects in it. A high thickness polyester glass fiber felt board with grade 155(F) of heat resistance is obtained by using the self-prepared vinyl resin and carbon-carbon intermediate temperature initiator under 120-125℃ and 7.5 MPa, and the problems of pores and cracks in the high thickness polyester glass fiber felt board are solved at the same time.

In order to analyze the influence of natural ester insulating oil on the insulating properties of power transformers, at first, the winding wave processes of a 110 kV natural ester insulating oil and a mineral insulating oil power transformers with the same insulation structure were calculated, and the longitudinal insulation margins of the two transformers were obtained. And then, the winding potential with linear distribution under power frequency and the nonlinear winding potential calculated by wave process were used as excitation sources respectively, the composite electric field of the two insulating oil transformers main insulation were simulated, and their distribution characteristics were compared and analyzed. At last, the main insulation margins of the two insulating oil transformers were calculated by using the whole-region electric flux line scanning method, and in view of the weak main insulation strength of natural ester insulating oil transformer, the structure was improved and the improvement effect was analyzed. The results show that through adding insulation paper boards and adjusting the size of oil ducts, the minimum insulation margin of the improved natural ester insulating oil transformer increases by 15.8%, which meets the requirements of main insulation strength, which provides a reference for developing large natural ester insulating oil transformer and optimizing its structure.

In order to explore the correlation between the aggregation structure of biaxially oriented polypropylene (BOPP) film and its breakdown property, and promote the localization of BOPP, the properties of four kinds of BOPP samples manufactured at home and abroad were compared by optical observation, X-ray diffraction (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), impregnation, and DC breakdown experiments. The results show that the BOPP film with higher crystallinity and higher segment activation energy has a larger electric strength. Impregnating the BOPO film with benzyl toluene can change its aggregation structure and improve the electric strength of electrical weak point. Compared with similar international products, domestic BOPP films show the gap of low electric strength, small shape parameters, and many electrical weak point.

The azodicarbonamide (AC) and aluminum hydroxide (ATH) were used to discuss the effect of their combination on the anti-tracking performance, mechanical properties, and hydrophobicity of silicone rubber composites. The possible reasons for AC and ATH synergistically improving the tracking resistance of the composites were discussed through scanning electron microscopy, contact angle, and other characterization methods. The results show that when the ATH is filled only, the filling amount must reach 100 phr, and the anti-tracking performance of silicone rubber composite can achieve grade 1A4.5. However, when the filling amount of AC and ATH are 3 phr and 80 phr respectively, with the help of the arc extinguishing and gas phase flame retardant effect of a large amount of nitrogen and carbon monoxide generated by the decomposition of AC, the anti-tracking performance of the silicone rubber composite also can achieve grade 1A4.5, and compared with the composite filled with pure ATH, it has better tensile strength and hydrophobicity, which is expected to be applied in the field of composite insulators.

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.