Morning Glory-Inspired Dual-Function Microcapsules for the Self-Reporting and Self-Healing of Electrothermal-Induced Damage of Electrical Devices.

The long-term operation of power equipment and power electronics can cause local overheating and discharges in the insulation material, resulting in irreversible insulation damage. Further development of such damage can eventually lead to equipment failure, but this problem is very difficult to solve. In this paper, inspired by how the petals of morning glory change color with the environment due to the presence of pigmented globules, a dual-function heat alert in the form of a self-healing (HASH) microcapsule with a nested structure is prepared by using microfluidic technology. By combination of the microcapsule with the insulation material, the local overheating in equipment can be detected promptly under live operating conditions without manual external intervention, and the defects that occur can be repaired autonomously. These HASH microcapsules can be pre-embedded in places at which the material is prone to overheating using artificial magnetic targeting. The doping of the matrix material with microcapsules does not cause any deterioration in its electrical or mechanical properties. This technology is expected to be applied to electrical equipment and electronic devices to allow for the early detection of local overheating and the autonomous repair of defects, thereby ensuring the safety of the equipment and improving its service life.

Self-Reporting Microsensors Inspired by Noctiluca Scintillans for Small-Defect Positioning and Electrical-Stress Visualization in Polymers.

Small defects induce concentrated electrical stress in dielectric polymers, leading to premature failure of materials. Existing sensing methods fail to effectively visualize these defects owing to the invisible-energy state of the electric field. Thus, it is necessary to establish a nondestructive method for the real-time detection of small defects in dielectric polymers. In this study, a self-reporting microsensor (SRM) inspired by Noctiluca scintillans is designed to endow materials with the ability of self-detection for defects and electrical stress. The SRM leverages the energy of a nearby electric field to emit measurable fluorescence, enabling defect localization and diagnosis as well as electrical-stress visualization. A controllable dielectric microsphere is constructed to achieve an adjustable electroluminescence threshold for the SRM, thereby increasing its detection accuracy while decreasing the electroluminescence threshold. The potential degradation in the polymer performance owing to SRM implantation is addressed by assembling long molecular chains on the SRM surface to spontaneously generate an interpenetrating network. Results of finite element analyses and experiments demonstrate that the SRM can effectively realize nondestructive visualization and positioning of small defects and concentrated electrical stress in polymers, positioning it as a promising sensing method for monitoring the electric field and charge distribution in materials.

In Situ Self-Fluorescence 3D Imaging of Micro/Nano Damage in Silicone Gel for Understanding Insulation Failure under High-Frequency Electric Fields.

Strong electromagnetic and heat flux stresses can induce severe damage to solid insulation materials, leading to faults in power equipment and power electronics devices. However, in the absence of suitable in situ imaging methods for observing the development and morphology of electrical damage within insulation materials, the mechanism of insulation failure under high-frequency electric fields has remained elusive. In this work, a recently discovered fluorescence self-excitation phenomenon in electrical damage channels of polymers is used as the basis for a laser confocal imaging method that is able to realize three-dimensional (3D) in situ imaging of electrical tree channels in silicone gel through nondestructive means. Based on the reconstructed morphology of the damaged area, a spatial equivalent calculation model is proposed for analysis of the 3D geometric features of electrical trees. The insulation failure mechanism of silicone gel under electric fields of different frequencies is analyzed through ReaxFF molecular dynamics simulations of the thermal cracking process. This work provides a new method for in situ nondestructive 3D imaging of micro/nanoscale damage structures within polymers with potential applications to material analysis and defect diagnosis.

Role of a 3D Nanoskeleton in Hindering Electrical Tree Growth in Nanocomposites: Insights from in Situ Self-Fluorescence Imaging.

Despite the proposal of nanodielectrics in 1994, the impact of nano- and microstructures on composite performance is still not completely understood. A key reason for this knowledge gap is the lack of in situ characterization of micro- and nanoscale structures within materials. In this study, we observed the self-excited fluorescence of a microscale-damaged microchannel inside a composite under the influence of an electric field. Furthermore, we conducted in situ imaging of the internal microstructures and discharge channels in the composite utilizing external laser excitation. The imaging results reveal that the electrical treelike damage in the composites grows with a single channel under the guidance of the nanoskeleton embedded in the matrix, which demonstrates that the three-dimensional (3D) nano-order skeleton hinders the development of electrical trees. Furthermore, we analyzed the nanoskeleton intervention's enhancement mechanism on the insulation properties of the composites. This work aids in the precision imaging-guided structural design of nanodielectrics.

Nondestructive 3D Imaging of Microscale Damage inside Polymers-Based on the Discovery of Self-Excited Fluorescence Effect Induced by Electrical Field.

The development of high-precision, non-destructive, and three-dimensional (3D) in situ imaging of micro-scale damage inside polymers is extremely challenging. Recent reports suggest that 3D imaging technology based on micro-CT technology causes irreversible damage to materials and is ineffective for many elastomeric materials. In this study, it is discovered that electrical trees inside silicone gel induced by an applied electric field can induce a self-excited fluorescence effect. Based on this, high-precision, non-destructive, and 3D in situ fluorescence imaging of polymer damages is successfully achieved. Compared with the current methods, the fluorescence microscopic imaging method enables slicing of the sample in vivo with high-precision operation, realizing the precise positioning of the damaged area. This pioneering discovery paves the way for high-precision, non-destructive, and 3D in situ imaging of polymer internal damage, which can solve the problem of internal damage imaging in insulating materials and precision instruments.

Magnetically Targeted, Water-Triggered, Self-Healing Microcapsules Based on Microfluidic Techniques Enabling Targeted Healing of Water Tree Damage in Epoxy Resins.

Repairing the micro-scale damage of insulating materials under a strong electric field has long been a highly desired but challenging task. Among all kinds of damage, water tree damage in the insulating materials of electrical equipment and electronic devices working in humid environments has long been considered irreparable. The main challenge is that residual water prevents the healing agent from filling the water tree branch channel. To solve this problem, this work reports a magnetically targeted, water-triggered, self-healing microcapsule (MTWTSH-MC) that makes a breakthrough against water tree damage based on microfluidic techniques. Targeted microcapsules driven by a directional magnetic field are concentrated to the vulnerable area of the insulating materials, exerting very limited effects on the dielectric. When damage breaks the microcapsules, the healing agent releases and quickly fills the damage channel and then reacts with water in the air or in the branch channel of the water tree, achieving solidification of the healing agent and self-healing of the damage channels. In this way, we can realize self-perception, self-triggering, and self-healing for both mechanical damage and water tree damage in insulation materials without any external stimulation.

A novel UV, moisture and magnetic field triple-response smart insulating material achieving highly targeted self-healing based on nano-functionalized microcapsules.

During the long-term operation of solid insulation materials, strong electric fields and mechanical stress cause electrical trees and cracks that are undetectable and irreversible, leading to the failure of electronic and electrical devices. A promising means of protecting against these problems is to endow the insulating materials with some self-healing capability alongside their excellent intrinsic properties. However, this has proved extremely challenging. In this paper, we describe an ultraviolet light, moisture, and magnetic field triple-response microcapsule that enables epoxy resin materials to heal themselves against various forms of damage without affecting the intrinsic performance of the matrix. In particular, microcapsules wrapped inside functional shells containing Fe3O4 nanoparticles are precisely controlled by a targeted magnetic field and distributed in the vulnerable area of the insulation materials, resulting in a high healing rate at low doping concentrations. Using the in situ ultraviolet light emitted by the electrical trees, artificial ultraviolet light, and moisture in the operating environment, it is possible to induce active or passive curing of the healing agent, thus realizing the intelligent, non-contact, and targeted self-healing of mechanical cracks and electrical tree damage. This method opens an avenue toward the development of self-healing insulation materials for electrical and electronic applications.

Novel Smart Insulating Materials Achieving Targeting Self-Healing of Electrical Trees: High Performance, Low Cost, and Eco-Friendliness.

It remains challenging to promptly inhibit and autonomically heal electrical trees inside insulating dielectrics, which are caused by sustained strong electrical fields and substantially shorten electronic device lifetimes and even cause premature failure of electrical equipment. Therefore, we demonstrate a magnetically targeted ultraviolet (UV)-induced polymerization functional microcapsule (MTUF-MC) to endow insulating materials with physical and electrical dual-damage self-healing capabilities. Specifically, Fe3O4@SiO2 and TiO2 nanoparticles, which serve as magnetic targets and UV shields (thereby preventing the healing agent from prematurely triggering), constitute a functional microcapsule shell, ensuring a low dopant concentration and excellent self-healing ability of the epoxy composites without affecting the intrinsic performance of the matrix. By exploiting in situ electroluminescence originating from electrical trees, UV-induced polymerization of healing agent is handily triggered without any applying external stimuli to intelligently, contactlessly, and autonomously self-healing electrical trees inside insulating dielectrics.

Physicochemical Characteristics and Dynamic Charge Mapping in Thermally Aged Two-Layered Polymer Considering Surface States: Experiment and Simulation.

Under operational conditions of high electric fields and elevated temperatures, the accumulation of space charges at multilayer insulation interfaces is often considered as an important factor affecting insulation performance. This study experimentally explored the influence of different thermal aging degrees (110 °C for 0, 720, 1600, 2100, and 2900 h) on physicochemical characteristics. The space charge dynamics in two-layered thermally aged PET-PET films were measured using the pulsed electro-acoustic (PEA) method and simulated on the basis of a one-dimensional modified bipolar charge transport model. The parameterization for key parameters involved in the model was analyzed through parameter sensitivity. Results indicated that the molecular structure, crystallinity, and dielectric spectra of the PET films are affected by thermal aging. The thermalization process also has noticeable effect on the surface state characteristics, which are characterized by deeper trap depth and larger trap density. Several experimental phenomena measured by the PEA method were observed on the basis of numerical simulation.

A Promising Nano-Insulating-Oil for Industrial Application: Electrical Properties and Modification Mechanism.

Despite being discovered more than 20 years ago, nanofluids still cannot be used in the power industry. The fundamental reason is that nano-insulating oil has poor stability, and its electrical performance decreases under negative impulse voltage. We found that C60 nanoparticles can maintain long-term stability in insulating oil without surface modification. C60 has strong electronegativity and photon absorption ability, which can comprehensively improve the electrical performance of insulating oil. This finding has great significance for the industrial application of nano-insulating oil. In this study, six concentrations of nano-C60 modified insulating oil (CMIO) were prepared, and their breakdown strength and dielectric properties were tested. The thermally stimulated current (TSC) curves of fresh oil (FO) and CMIO were experimentally determined. The test results indicate that C60 nanoparticles can simultaneously improve the positive and negative lightning impulse and power frequency breakdown voltage of insulating oil, while hardly increasing dielectric loss. At 150 mg/L, the positive and negative lightning impulse breakdown voltages of CMIO increased by 7.51% and 8.33%, respectively, compared with those of FO. The AC average breakdown voltage reached its peak (18.0% higher compared with FO) at a CMIO concentration of 200 mg/L. Based on the test results and the special properties of C60, we believe that changes in the trap parameters, the strong electron capture ability of C60, and the absorption capacity of C60 for photons enhanced the breakdown performance of insulating oil by C60 nanoparticles.

Failure Characteristics and Mechanism of Nano-Modified Oil-Impregnated Paper Subjected to Repeated Impulse Voltage.

Nano-modification is a prospective method for improving the electrical properties of transformer oil. In most situations, transformer oil combined with cellulose paper is used to construct an insulation system for power equipment, such as power transformers. However, the influence of nanoparticles on the electrical performance of oil-impregnated paper is still unclear. Therefore, in this paper, we identify the failure characteristics of both fresh and nano-modified oil/paper. Specifically, the accumulative failure characteristics of nano-oil-impregnated paper (NOIP) are experimentally determined. The space charge distribution and trap characteristics of fresh paper and NOIP were measured, and the effect of nanoparticles on the space charge behavior are then analyzed. Finally, we measure the microstructure of fresh paper and NOIP subjected to repeated impulses. The test results indicate that nano-titanium oxide (TiO2) particles have a limited effect on the breakdown voltage of NOIP. However, the particles can dramatically improve the resistant ability of NOIP against repeated impulses. For the NOIP with a nano-concentration of 0.25 g/L, the improvement reaches 62.5% compared with fresh paper. Under repeated applications of impulse voltages, the space charge density of NOIP is much lower than that of fresh paper. The deep trap density of NOIP is much higher than that of fresh OIP, whereas shallow trap density is relatively lower. Micropores are generated in paper insulation subjected to repeated impulses. The amount of the generated micropores in NOIP is lower than that in fresh paper. Nano-TiO2 particles suppress the accumulation of space charge in the oil paper insulation, which weakens the electric field distortion in the dielectric. However, nanoparticles reduce the accumulative damage caused by repeated impulses. The above two points are considered the main reasons to improve the resistant ability against repeated impulses.