The temperature difference in the southeastern region of Tibet is relatively large, which has negative influence on the insulation performance of composite insulators, and affects the continuous and reliable transmission of West East power. Silicone rubber samples were conducted 720 hours of high and low temperature cyclic ageing tests at -20-150℃ in this paper, and the silicone rubber sampes with different cycles were conducted various tests to study the changes of ageing performance in large temperature difference environments. The 12 kinds of tested characteristic parameters were conducted selection of characteristic parameters using Fisher Score, and 4 kinds of significantly correlated characteristic parameters were selected. Taking composite insulators running for 0-11 years as the research object, we conducted performance testing and result analysis on in-service composite insulators based on correlated characteristic parameters, and proposed an improved genetic algorithm to optimize the BP (Back Propagation) neural network prediction algorithm. On the one hand, this algorithm improves the optimal preservation strategy selection operator, and on the other hand, this algorithm dynamically adjusts the mutation probability and crossover probability during the iterative process. The results show that the four ageing characteristic parameters, which are tensile strength, dielectric loss factor tanδ, TGA residual ratio, and Si-OH transmittance reduction rate, are significantly correlated. Compared with the traditional BP and GA-BP (genetic algorithm back propagation) neural networks, the improved GA-BP neural network has stronger nonlinear learning and global optimization capability, and faster network convergence speed. The test error result of the improved GA-BP neural network on a group of samples aged for 11 years is 2.33%. The error between the predicted operating life and the actual service life of five groups of composite insulators is within 5%.

Moisture intrusion and residual conductive particles are common defects in the joints of tubular insulated busbars in substations. These defects would cause distortion of electric field distribution at the joints, endangering insulation performance and potentially leading to insulation breakdown, burning, and other accidents. In this paper, finite element multi-physics simulation technology was used to construct a joint model of tubular busbar with wrapped insulation material based on the actual structure. Three types of water films, with 10, 30, and 50 mm of lengths, and semi-circular conductive impurities with 0.5 mm of radius, were placed at the interfaces between the metal shielding layer and the main insulation layer, as well as between the main insulation layer and the inner sealing layer. COMSOL software was used to conduct electric field simulation analysis, and the impact of different defects located at various interfaces on the electric field distribution of tubular insulated busbar joint was studied. The results show that both water films and conductive impurities can impact the electric field distribution at the insulation layer interfaces to different degrees. The electric field strength inside the defects decreases, while the electric field strength at the defect edges increases dramatically. Among these, the electric field distortion with conductive particles at the insulation interface is more severe than that with moisture intrusion, making insulation breakdown faults more likely. Therefore, it is crucial to enhance the end sealing and strictly prevent the presence of residual conductive particles.

The surface charge accumulation of basin insulators is one of the important factors restricting the development of HVDC GIL, and the heat transfer inside the GIL would aggravate the surface charge accumulation. In this paper, an electrical-thermal coupling simulation model of charge accumulation was established. The time-varying temperature distribution inside the GIL under different external ambient temperature and gas pressure was simulated. The surface charge accumulation characteristics under constant and time-varying external ambient temperature were studied, and its effect on the surface charge accumulation was also analyzed. The results show that when the external ambient temperature is a constant value, the external temperature increases every 10℃, the steady-state temperature on the insulator surface increases by more than 9.2%, and the steady-state surface charge density of insulator increases by more than 17.3%. When the external ambient temperature changes with time, the temperature on the insulator surface eventually fluctuates with time around a stable value after continuously rising for a period of time, and the surface charge density is approximately equal to that under the average external ambient temperature. In addition, the surface temperature and charge density of the insulator decrease with the increase of gas pressure. The research results are expected to provide reference for the design and operation of DC GIL, which can improve the safety and stability of DC GIL operation.

Fiber reinforced epoxy resin composites are widely used in electrical power equipment. However, due to their complex preparation process and multi-layered structure, internal defects are prone to be introduced during manufacture, which may lead to partial discharge and even breakdown under long-term high voltage operating condition. Early detection of these defects can significantly reduce the occurrence of failures. In this paper, an ultrasonic testing system for composite was established on the basis of ultrasonic reflection method, and various plate samples of glass fiber reinforced epoxy resin composites containing artificial crack, delamination, and metal impurity defect were prepared on the basis of vacuum assisted resin infusion molding method. Ultrasonic testing and spectral analysis were then conducted on these defect-containing plate samples. The results indicate that there are significant differences in the ultrasonic reflection waveforms for different defects of samples. By transforming the ultrasonic echoes into frequency spectra, the normalized spectral characteristic curves are obtained, and different types of defects can be identified by calculating the characteristic values from these curves. The characteristic value of the sample with crack defect is the smallest, and the characteristic value of the sample with delamination defect is the largest.

Umbilical cables are known as the "nerve lifeline" connecting underwater production systems and upper facilities, and accurate analysis of their temperature field distribution and ampacity is a key guarantee for safe offshore oil and gas exploration and production tasks. Unlike traditional submarine cables, umbilical cables have complex electro-thermal-fluid multi-physical fields coupling effects due to their complex structure and diverse functions, and it is difficult to determine their temperature field distribution and ampacity by traditional analytical methods. A fine cross-sectional model of multi-field coupling of umbilical cable was established based on the finite element software COMSOL in this paper, and the influence of three typical laying methods, environment and other factors on the conductor temperature and steady-state ampacity was studied by the control variable method. The results show that when the current is small, the temperature of the fluid in tube is the dominant factor affecting the cross-sectional temperature and steady-state ampacity of umbilical cable. The trend of conductor temperature can reflect the change of steady-state ampacity. When buried directly, the increase of buried depth and the external fluid temperature will weaken the heat dissipation capacity of umbilical cable. When tiled, the seawater flow significantly reduces the temperature of umbilical cable, and at low flow rates, the increase of flow rate has a significant cooling effect on the umbilical cable. However, the high flow rate of seawater will form a boundary layer with temperature gradient on the surface close to the umbilical cable, making the heat transfer be restricted, and the cooling effect is not obvious. The insulation ageing has less influence on the overall temperature distribution of umbilical cable, but it affects the maximum temperature of the cross-section.

High-power air-insulated RF coaxial cable has a broad application prospect in the field of Internet of Things. It is of great significance to study the electric field distribution of its important insulating component—insulating gasket in the presence of common defects for the safe and stable operation of RF coaxial cables. Firstly, a numerical model of RF coaxial cable containing inner and outer conductors and insulating gaskets was established and a simulation model of electrostatic field was constructed in finite element software, and the accuracy of the model was verified through experiments. Secondly, on the basis of constructed model, the effects of internal air bubbles, surface foreign objects, and interface defects on the electric field distribution of insulating gaskets were studied by adjusting the morphology and positional parameters of defects, and compared with the simulation results of electric field intensity in the absence of defects. The results show that the electric field distribution of the insulating gasket is related to the morphology of internal bubbles, and the closer the distance from the inner conductor, the more serious the electric field distortion; the size, location, and arrangement of the surface foreign objects will affect the electric field distribution, and the influence of conductive particles on the electric field is larger than that of sand particles; the interface defects have a negative correlation with the thickness of defects, and have a positive correlation with the depth of defects. In summary, it is surface foreign object leading to the most serious electric field distortion in three kinds of defects, followed by interface defect.

The application of conventional polyimide in the insulation structure of rail transit traction motors is prone to corona breakdown failure, which seriously affects the reliability and safety of the motor's long-term operation. In this paper, three corona-resistant polyimide materials were prepared by using 4,4′-diaminodiphenyl ether (ODA) as the diamine, pyromellitic dianhydride (PMDA) as the dianhydride, and nano-alumina surface treated with different silane coupling agents as the inorganic filler. The impact of various coupling agents on their surface morphology, mechanical properties, corona-resistant lifetime, and electrical breakdown performance were investigated. The results show that the surface treatment with silane coupling agents can improve the dispersibility of alumina in the polyimide matrix, reduce the agglomeration of nano-alumina, and enhance the corona-resistant properties of the polyimide material, while its excellent mechanical properties are maintained. Among them, the dispersion stability of nano-alumina surface treated with bis-amino silane coupling agent is the best, and the prepared corona-resistant polyimide material also has the best surface morphology and comprehensive performance. The corona-resistant time is 25 min and 120 min, respectively under 3 kV and 2 kV, the tensile strength reaches 167 MPa, and the elongation at break is 29.5%.

In order to solve the problem of printing contamination on the surface of silicone rubber cables, the application of low temperature plasma jet in surface treatment of silicone rubber was proposed in this paper. Ar plasma jet was generated with needle-ring structure electrode driven by AC power source, and the surface of silicone rubber cables was dynamically treated at different moving speeds. The influence of processing speed on the hydrophobicity, surface voltage, and breakdown strength of silicone rubber cable was systematically studied. The changes in surface physical morphology and chemical composition of silicone rubber were detected by SEM and EDS. The results show that static jet treatment can cause an increase of the material surface temperature, while dynamic treatment can significantly reduce the temperature rise. The water contact angle and flashover voltage of silicone rubber slightly decrease after treatment. With the increase of processing speeds, the hydrophobic and electrical insulation performance gradually recover. Under the speed of 5 mm/s, the anti-ink adhesion of silicone rubber surface is significantly improved. It can be concluded that the degree of cross-linking polymerization on the surface of silicone rubber increases after the plasma jet treatment, and the diffusion movement of interface molecules at the interface is hindered, which decrease the anti-ink adhesion of the silicone rubber surface.

Taking the DC submarine cable in ±525 kV DC transmission project as the research object, we conducted DC voltage withstand test, impact voltage withstand test, and gradient voltage withstand test. The breakdown strength, ageing life index, Bahder's coefficient and other key parameters of the insulation material were analyzed. The insulation thickness of the ±525 kV DC cable under different voltage withstand condition was designed and calculated. The insulation design thickness was calibrated on the basis of the electric field distribution and temperature distribution of DC cable. The results show that the distortion degree of electric field distribution in DC cables is mainly determined by the temperature difference of insulation layer, and the insulation temperature difference is mainly determined by the magnitude of current passing through the cable conductor. Taking into account the research results and the long-term safety and reliability of cable, it is recommended that the insulation thickness of ±525 kV DC cables is designed to be 28 mm.

To solve the problem that frequency domain reflectometry (FDR) can only distinguish defect polarity and cannot identify the defect length and type, a defect type discrimination method was proposed on the basis of signal attenuation intensity evaluation in this paper. The difference between the total refracted reflection intensity at each defect and the initial reflection intensity was calculated, and then the defect length and type can be discriminated by comparing the magnitude of difference. Combined with the polarity judgment method, the defect can be subdivided into four types. The results show that the method proposed in this paper can successfully identify the length and type of four common defects in cables, including grounding faults, excessive bending, cable body moisture, and long intermediate joints of cables, and the recognition results are consistent with the simulation modeling results. The defect type discrimination method in this paper can identify the common point defects and segment defects in cables.