In view of the problem of uneven electric field distribution and severe local electric field distortion in insulation partitions of high-voltage switchgear, dielectric functional gradient materials were introduced into the preparation of insulation partitions, and two optimization schemes, which are internal insulation structure optimization and surface insulation structure optimization, were proposed. By changing the upper limit of dielectric constant of material, the thickness of insulation partition, and the thickness of surface coating, electric field and temperature field simulation calculations were carried out to compare and analyze their effects on the optimization of electric field distribution. Finally, simulations and dielectric loss characteristics tests were conducted to compare the two optimization schemes. The results show that compared to the traditional homogeneous insulation partitions, changing the internal insulation structure and adding surface coatings can reduce the maximum field strength along the surface without considering the influence of internal operating environmental factors in the switchgear. When the thickness of insulation partition increases to 12 mm, the electric field optimization effect is optimal, and the maximum field strength along the surface can be reduced by 69.8%. When the surface coating thickness is 1 mm, the electric field optimization effect is optimal, and the maximum field strength along the surface can be reduced by 62.9%. Through simulation and experimental comparison, it is proved that the partition with optimized internal insulation structure has better electric field control effect and insulation performance.

In recent years, attentions on smooth aluminium sheathed cables has continued to increase in China, but at present, the researches on the laying of smooth aluminium sheathed cables are still insufficient. Conductor heating caused by thermo-mechanical stress during laying process of cable may cause safety problems. In this paper, a finite element model of smooth aluminium sheathed cable under vertical serpentine laying was established, and the thermo-mechanical effect of the cable was calculated and analyzed. The results show that the vertical serpentine laying of cable would generate serpentine arc lateral slip, making the axial force induced by thermal effect much smaller than that of the straight laying of cable, which meet the long-term safe operation conditions of cable. With the increase of temperature, the lateral slip of vertical serpentine laying gradually increase, the increase trend is consistent with the theoretical calculation results, and the axial force changes from tensile force to compressive force and then gradually increase. By appropriately increasing the arc width and semi-serpentine pitch of vertical serpentine laying of cable, the axial force of cable can be reduced.

In cable accessories, the interface between cable body insulation and accessory insulation often coat with insulating oil for cable to enhance the sealing and insulating properties between the interfaces of cable accessories. In order to investigate the compatibility and applicability of cable body insulation and insulating oil, and to provide a reference for the selection of insulating oil for cables, the adsorption compatibility of PP and XLPE on three typical insulating oils (silicone oil, silicone grease, and polyisobutylene) at 25℃ and 75℃ was studied. The results show that affected by the molecular structure, PP and XLPE have limited adsorption capacity on silicone oil and silicone grease, and they can easily adsorb polyisobutylene, resulting in a significant increase of quality. PP coordinating with silicone grease have the best properties, which can improve the mechanical properties and electric strength of PP. XLPE exhibits close properties in silicone oil and silicone grease, among which silicone grease impregnation maintains good mechanical properties, while silicone oil impregnation maintains good insulating properties. Through analysis it is found that appropriate amount of adsorption improves the surface roughness, fills the internal defects of the insulation, and improves the insulating properties of material. By studying the influence of different types of coating materials on the main insulating material at different temperatures, the adaptability results of insulating medium and cable main insulation are obtained, which can provide a reference for standardizing the selection of insulating oils for cable terminals and improving the operating reliability of cable terminals.

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%.

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.

Submarine cable is a transmission component of high-voltage power, and the heat generated during the operation of submarine cable will cause the structural temperature rise and expand. Under the constraint of each layer, the submarine cable will produce large thermal stress and deformation, which will cause structural damage. In addition, the increase of temperature will lead to the decrease of elastic modulus of the polymer material inside the submarine cable, resulting in the change of mechanical properties of the submarine cable section. Therefore, it is necessary to study the stress and deformation caused by thermal expansion during the operation of submarine cables, and analyze the influence of temperature on the mechanical properties of submarine cables. In this paper, based on an offshore wind power project, a finite element model of submarine cable-soil was established in finite element software ABAQUS, and the temperature field distribution under steady-state current carrying capacity was obtained. Based on the results of temperature field, the thermal stress and thermal deformation of the submarine cable were calculated by the thermal-mechanical coupling method, and the change of mechanical properties of the submarine cable section under the action of temperature was analyzed. The results show that the highest temperature appears in the copper conductor during the operation of submarine cable, and the outer coating layer has the lowest temperature. With the copper conductor as the center, the temperature drop gradient along the inside radial direction is small, and the temperature drop gradient along the outside radial direction is large. The thermal stress is mainly concentrated in the metal structure, and the maximum deformation occurs in the steel wire armor. When the copper conductor and the optical fiber are located at the top of the cross section, the displacement is the largest, and the displacement is the smallest at the bottom. After considering the influence of temperature, the stress of copper conductor and optical fiber will increase, while the tensile and torsional stiffness of submarine cable will decrease, and the reduction of inverse torsional stiffness is greater than that of clockwise torsional stiffness.

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.

Silicone rubber composites are widely used in wire and cable, electronic packaging and other fields due to their excellent weather resistance, electrically insulating properties, high chemical stability and other advantages. In this paper, the research progress of filled thermal conductive and electrically insulating silicone rubber composites was reviewed from the aspects of thermal conductive mechanism, influencing factors of thermal conductivity, and strategies to improve the thermal conductivity of silicone rubber composites, and the research prospects of filled thermal conductive and electrically insulating silicone rubber composites were prospected.

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.

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.