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.

To address the limitations of traditional methods in accurately detecting micro-defects in epoxy-based insulation, we proposed a novel defect detection method based on photon emission counting analysis under different defect influence. Insulation rod and insulation spacer samples with scratches, surface protrusions, and metal particles were prepared, and their photon counting before partial discharge inception was tested under AC voltage excitation. The results indicate that the average photon counting of samples with severe defects is 12 times higher than that of samples without defects. The photon counting results are significantly influenced by defect types, sizes, position, and insulation gas, and the average photo counting is positively correlated with the defect severity. Therefore, the photon counting can be as a promising tool for early detection of defects in epoxy-based insulation materials.

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.

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.

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.

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.

Epoxy resin has been widely used in the field of insulating materials due to its excellent mechanical properties, thermal stability, chemical stability, and electrical insulation. The stable three-dimensional cross-linked network structure not only gives epoxy resin excellent properties, but also brings great difficulties to its reprocessing, degradation, and recycling. At this stage, more and more researches have begun to focus on the environmentally friendly epoxy resin materials to solve problems such as reprocessing and degradation. In this paper, several typical design ideas and methods of epoxy resin based on dynamic covalent bonds were reviewed, and the environmentally friendly epoxy resin materials through introducting ester bonds, disulfide bonds, silicon-oxygen bonds, imine bonds, D-A structure, acetal bonds, host-guest interaction, and multiple dynamic bonds into the epoxy resin were introduced emphatically. Meanwhile, it is introduced that the topology structure of epoxy resin cross-linked network can be reversibly changed by dynamic covalent bonds under certain stimuli to realize the function of remodeling, reprocessing, self-repairing, and degradation. Finally, the application prospects of insulating materials based on dynamic covalent bonds were summarized and prospected.

The frequent disconnection of inverter power devices and load characteristics of motor can lead to high-frequency pulse overvoltage, which would lead to premature failure of generator insulation and bring challenges to the stability and reliability of system. From the failure mechanism of inverter motor insulation, the different stress failure forms of inverter motor insulation were investigated firstly, and the main factors affecting the failure of the insulation system were sorted out. Then the state detection methods of inverter motor insulation and the delay measures were comprehensively reviewed. Finally, the major challenges and future research direction currently faced by inverter motor insulation were emphasized.

In this paper, the general rules and characteristics of the failure damage of basin insulators in recent years were firstly summarized. Then, the typical failure area of sample was extracted to analyze the matrix microstructure morphology and the failure fracture surface morphology. Finally, the micro mechanical properties of the heterogeneous interface in composite materials were characterized and analyzed by nanoindentation mechanics technology, and the crack initiation and failure fracture mechanism of Al₂O₃/epoxy resin composite materials were expounded. The results show that the fracture toughness value of the epoxy resin matrix is about 0.55 MPa·m^1/2, and the cracks originate from the epoxy resin matrix under the action of load and continuously expand. When encountering high-strength Al₂O₃ particles, the cracks deflect due to the retardation and rapidly expand along the interface between the particles and matrix.

The "thermal expansion and contraction" behavior of the internal atoms in epoxy resin and the intrinsic issue of low thermal conductivity seriously restrict the application of epoxy resin in dry-type DC sleeve insulation. To address this, we introduced boron nitride whiskers with low thermal expansion coefficient into epoxy resin to prepare a new boron nitride whisker/epoxy (BNw/EP) composite dielectric, and its microstructure, thermal expansion coefficient, thermal conductivity, electrical properties, thermal stability, and mechanical properties were tested and analyzed. The results show that within the temperature range of 20-100℃, the thermal expansion coefficient of the composite dielectric with 10% mass fraction of boron nitride whisker is reduced by 15% compared to pure epoxy resin, while the thermal conductivity increases to 0.28 W/(m·K), which is 33.33% higher than that of pure epoxy resin. In addition, its dielectric constant is below 5.28 and the dielectric loss is below 0.02 in the frequency range of 10²-10⁶ Hz, the volume resistivity is 10¹⁴ Ω·cm, and the tensile strength is maintained at about 49.5 MPa. This study proves that on the basis of ensuring the insulation, dielectric and mechanical properties of the composite dielectric be not damaged, filling the epoxy resin matrix with boron nitride whiskers can effectively reduce the thermal expansion coefficient of the material and improve the thermal conductivity.