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.

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.

No abstract

Surface discharge phenomena often occur across the insulator in power systems, damaging the electrical equipment, but the mechanism of the electron multiplication stage during surface discharge is not yet fully understood. As such, it is necessary to investigate the mechanism of discharge along a dielectric surface. In this paper, we develop a numerical fluid model, analyzing the dynamic characteristics of discharge including the electron density, electron temperature, surface charge density, and electric field. Our results show that the electron density peaks in the head of the streamer channel, at which time the electron temperature also reaches its maximum. A thin layer of plasma can be formed, filled with a mix of positive and negative charges, so the space normal electric field in the streamer channel can be positive or negative. In addition, the surface tangential electric field and electric potential are closely related, and the potential steadily increases because there is a steady tangential electric field in the streamer channel.

Operation of a high-voltage, direct current circuit breakers can cause irreversible damage to the surface electrical performance of insulation due to arc ablation. To analyze the failure mechanism, the epoxy resin (EP) insulation was ablated under experimental arcs of different energy values. The rated current of the experimental arc is 5 A, and the ablation energy values were set as 0 J, 31.3 J, 78.2 J, 109.6 J and 156.5 J respectively by changing the arc duration. The destruction of the EP surface molecule structure was investigated by using x-ray photoelectron spectroscopy and gas chromatography. Furthermore, the surface potential decay and distribution characteristics of surface traps were studied by using the isothermal surface potential decay (ISPD) method. The test results indicate that when arc energy reaches 156.5 J, the DC flashover voltage of EP decreases by 64.7% and the surface conductivity increases by 3.22 times, compared with that of the virgin sample. Reductive groups in EP molecules are oxidized when suffering arc ablation, thereby leading to the breakage of molecular chains and severe carbonization, forming amorphous carbides with high conductivity on EP surface. ISPD results show that the density of deep traps and the center energy level of traps on the EP surface increase when the arc energy increases. These traps can form multiple charge centers and distort the electric field distribution on the EP surface. Thus, the partial discharge is promoted and flashover finally occurs, thereby decreasing the surface electrical strength of EP.