In the study of damage mechanisms of composite materials, acoustic emission (AE), as a nondestructive testing technique, has gained excellent application results due to its high accuracy, real-time performance, insensitivity to geometry, and wide application prospects. In this paper, the analytical methods and application status of acoustic emission technology on damage mechanism of composite materials were summarized, the advantages and disadvantages of acoustic emission technology in the study of damage mechanism of composite materials were comprehensively elaborated, and the key technologies that need to be solved urgently were also explored, and the prospects of its application in the field of composite materials were envisioned.

In order to develop a safe and eco-friendly accelerator, the differences between zinc neodecanoate and zinc naphthenate were studied from the three aspects of volatility characteristic, Zn²⁺ ion content, and the promoting curing characteristics of epoxy anhydride resin. Using high purity bisphenol A epoxy and methyl hexahydrophthalic anhydride as resin matrix, zinc neodecanoate and zinc naphthenate accelerators was added to the resin matrix,respectively. And then resin cured samples were prepared through the same process, and the glass transition temperature (T_g) and thermogravimetric curves of the samples were tested. The results show that due to the characteristic of single molecular structure, high Zn²⁺ content, and very low volatile organic compounds (VOCs), zinc neodecanoate is environmentally friendly. Comparing to zinc naphthenate, zinc neodecanoate requires a higher temperature to ensure complete curing of the epoxy anhydride resin. But under the same existing process conditions, the T_g of cured sample accelerated by zinc neodecanoate can reach 152℃, which is 11℃ higher than that of zinc naphthenate (141℃), indicating that the cured product accelerated by zinc neodecanoate has better thermomechanical properties.

In order to investigate the application of laser-induced breakdown spectroscopy (LIBS) technology in rapid quantitative detection of insulator contamination, and improve the accuracy and speed of insulator contamination detection, a detection platform based on LIBS technology was established to test artificial and natural contamination samples. The artificial contamination samples were formulated by mixing NaCl, CaSO₄, CaCO₃, and kaolin, while the natural contamination samples were taken from silicone rubber insulators which had been in operation for two and four years in a regional power grid in southern China. The rapid quantitative detection of insulator contamination was carried out by means of the calibration-free LIBS method. The results show that there are 9 kinds of elements with different proportions in the two artificially contaminated samples, while the two naturally contaminated samples contain 9 and 11 distinct elements, respectively. After self-absorption correction, the contaminant elements of the insulators are presented as neatly arranged distribution points on the Boltzmann plot, with consistent regression line slopes, and high fitting degrees, and the spectral line intensities of each element enhances significantly. This effectively mitigates the impact of self-absorption on rapid quantitative detection of insulator contamination, and improves the detection accuracy.

The research progress of epoxy resin reinforced by different types of fillers, including carbon nanomaterials, ceramics, metals, and natural fillers in recent years was reviewed. The reinforcement effects of types, dispersion, and surface modification of fillers on the mechanical properties of epoxy resin were summarized in detail. And the research and development direction of reinforced modification of epoxy resin were also prospected.

A high phosphorus content epoxy resin (DPOEP) was synthesized by using 2,5-dihydroxybenzyl(diphenyl)phosphine oxide (DPOHQ) and epichlorohydrin (ECH) as reactants, and then the structure of DPOEP was characterized by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The curing reaction characteristics of DPOEP with the curing agent of active ester resin DFE617 was studied, and the effects of DPOEP content and phosphorus-containing epoxy resin structure on the flame-retardant performance, dielectric properties, and thermal stability of dicyclopentadiene (DCPD) epoxy resin curing system were investigated. The results show that the curing process of DPOEP/DFE617 system follows a first-order reaction. DPOEP can promote the carbonization of condensed phase in the DCPD epoxy resin/DFE617 system, and the limiting oxygen index of cured resin reaches 36.6%-38%, achieving V-0 rating in the UL94 test. The dielectric loss factor of the epoxy resin curing system decreases with the increase of DPOEP content. At a lower content of DPOEP, the epoxy resin cured material is halogen-free and flame retardant while maintaining good thermal properties.

In order to investigate the ageing characteristics of the FRP/RPUF interface of composite insulation cross-arm under the effect of water intrusion, FRP/RPUF interface specimens were prepared, and water intrusion and destruction process in the FRP/RPUF interface was accelerated by hygrothermal ageing method. According to the test results of water absorption, shear strength, and leakage current, the ageing characteristics of the FRP/RPUF interface under water intrusion were obtained by combining with SEM, FTIR, and TGA. The results show that water intrusion can cause moisture plasticisation of the interface, reduce the shear strength and increase the leakage current, while that destructive effects decrease with the dissipation of water; hydrolytic reaction of FRP/RPUF interface material undergoes under the effect of water, leading to the generation of local defects and the increase of impurity ions, which further destroys the mechanical and electrical properties of the interface.

In order to study the effect of coating silicone grease on the distribution of multiple physical fields at the crosslinked polyethylene/silicone rubber composite interface under thermal ageing, the electrical-thermal-mechanical multi-physics field model of 110 kV cable terminal joints was established using COMSOL Multiphysics software. The distribution of electric field, temperature field, and stress field at the composite interface before and after coating silicone under thermal ageing was simulated. The results show that after coating with silicone grease, the sealing degree of the interface increases, which decreases the distortion degree of the electric field and leads to the slight decrease of the temperature rise of the interface, but the stress of the interface distributes unevenly. After ageing, the swelling of silicone grease on silicone rubber increases the relative dielectric constant of silicone rubber, and the interfacial charge density, and causes the electric field strength increase further. The increase of temperature promotes the penetration of silicone grease to silicone rubber, which decreases the thermal conductivity of silicone rubbe and make the interface temperature higher than that before ageing. Under thermal ageing, the elastic modulus of the silicone rubber coating with silicone grease decreases significantly and the interfacial stress decreases further.

The partial discharge ultrasonic signal attenuates severely on power transformer equipment shell, resulting in larger differences in the partial discharge signals received by different positions of sensors, which greatly affects its measurement accuracy and detection efficiency in field application. In this paper, a partition model of oil-immersed power transformer was built using finite element simulation software, the partitioning rule of partial discharge ultrasonic signal on the main surface of oil tank was obtained, and the transformer spatial sound pressure and partition sound pressure distribution maps were formed. On the basis of monitoring point optimization method of Pearson correlation coefficient and K-means clustering, the monitoring points with the best sensitivity of spatial sound pressure and partition sound pressure were preferably selected and compared. The results show that the average detection efficiency of the A-level monitoring points is 86.0%, which realizes the efficient detection of transformer partial discharge and provides a new method for selecting the placement points of ultrasonic sensors.

Vegetable insulating oil has gained wide attention due to its green and renewable characteristics as well as excellent fire protection properties, while nanoparticles can effectively improve the electrical properties of vegetable insulating oil. In this paper, the effects of nanoparticles on the electrical properties of vegetable insulating oil were summarized from dielectric loss factor and volume resistivity, and the effects of nanoparticle type, concentration, and surface modification on the breakdown properties of vegetable insulating oil were also discussed. Combining with the differences in the effects of nano-modification on the electrical properties of mineral insulating oil and vegetable insulating oil, we summarized the current research difficulties of nano modified vegetable insulating oil, and prospected the research direction and prospects of nano modified vegetable insulating oil.

Transformer oil is prone to microbial contamination during storage, utilization, and transportation, which affects the quality and insulating performance of transformer oil. In this study, the effects of temperature and humidity on the microorganism growth in transformer oil were mainly investigated, and the quality changes of transformer oil before and after treatment were analyzed. The functional group structure and organic species of transformer oil were identified, and some effective treatment methods for microbial pollution in transformer oil were proposed. The results show that both the transformer running oil and faulty oil contain bacillus subtilis, bacillus using sugar to produce acid, bacillus using sugar to produce acid and gas, and bacillus producing acid and gas without sugar. The number of microorganisms in faulty oil is much greater than that in running oil, and the number of bacillus subtilis is the largest, while there is no microorganism cultured in new transformer oil. The high temperature could restrict the growth of microorganism in transformer oil. When the temperature is 60℃, the microorganisms will not be completely inactivated, and once the temperature returns to 37℃, they will start to grow and reproduce again. When the mass ratio of oil and water is 99∶1, 49∶1, 19∶1, and 9∶1, four types of bacillus all exist at 37℃, and the number of bacillus increases with the increase of oil-water mass ratio. The regeneration treatment method of high-pressure sterilization+molecular sieve coarse filtration+ultrafiltration can make the contaminated transformer oil clear and transparent, and the microorganisms disappear. The regenerated oil mainly contains O-H, C-H, C=O, and unsaturated bonds. After regeneration treatment, the breakdown voltage and volume resistivity of transformer oil increase from 25.83 kV and 5.70×10¹⁰ Ω·m to 49.50 kV and 4.68×10¹¹ Ω·m, respectively, and the dielectric loss factor decreases from 6.052% to 0.215%, which meet the requirement of DL/T 1419—2015.