Epoxy resin is widely used in the field of electrical equipment insulation. In this paper, the effects of mechanical stress on cohesive energy and energy level distribution of epoxy resin were investigated. Tensile stress reduces the cohesive energy density of epoxy resin and accelerates the insulation deterioration. On the contrary, the compressive stress can restrain the insulation deterioration. The van der Waals interaction plays a more important role in changing the cohesive energy. The band gap of epoxy resin decreases and the polarizability increases under tensile stress. Under compression stress, the band gap increases and the polarizability decreases. The changes of molecular local state and polarization can affect the charge transport characteristics, which reveals the relationship between the insulation deterioration and the mechanical stress. The conclusion is helpful to understand the insulation failure mechanism of epoxy resin under mechanical stress.
Transforming growth factor β 1 (TGF-β1), as the most abundant signaling molecule in bone matrix, is essential for bone homeostasis. However, the signaling transduction of TGF-β1 in the bone-forming microenvironment remains unknown. Here, we showed that microRNA-191 (miR-191) was downregulated during osteogenesis and further decreased by osteo-favoring TGF-β1 in bone marrow mesenchymal stem cells (BMSCs). MiR-191 was lower in bone tissues from children than in those from middle-aged individuals and it was negatively correlated with collagen type I alpha 1 chain (
In this paper, the mechanisms of surface charging and surface modification of epoxy spacer affecting the lifting voltage of spherical metal particles in a down-sized DC GIS are investigated by simulations and experiments. Results show that Pre-stressing leads to a 27% decrease of lifting voltage, which is traceable to that surface charging make a major contribution to the enhancement of electric field force. The lifting voltage of metal particles around the epoxy spacer are markedly increased by fluorination, which is a promising treatment for DC GIS application. The lifting behavior of metal particle is significantly inhibited after treatment because of less surface charge accumulation and more rationalized electric field distribution. Direct fluorination is proved as an effective modification method to improve the insulation performance of epoxy spacer again.
The power leading insulation of high-temperature superconductivity (HTS) equipment has to confront the electric field concentration and huge temperature differential, which puts forward higher requirements for insulation materials. Surface flashover will lead to the failure of the power leading insulation. Ethylene propylene diene terpolymer (EPDM) has been proved to be a potential application in HTS power leading insulation. Doping of carbon black (CB) nanoparticles into EPDM can improve the polymer insulating properties for HTS equipment. However, the effects of low temperature on flashover as well as the correlated trap distribution of CB-filled EPDM have not been completely researched. In this paper, the samples were prepared by mixing CB nanoparticles into EPDM with the content of 0, 1, 3, and 5 wt%. The depolarization current was measured to estimate the trap characteristics of the nanocomposites at the temperatures of 193, 243, and 293 K. Needle-plate flashover experiments were performed at the same condition. Obtained results indicate that low temperature will change the effect of nanoparticles doping on the depolarization current and trap distribution. The surface flashover strength is significantly promoted by CB nanoparticle doping, which has strong correlation with the trap characteristics.
Silicone rubber (SiR) has been an important material widely used in the cable accessories in cross-linked polyethylene (XLPE) cables. The electrical tree is a serious threat to SiR insulation and it will cause breakdown when reaches the ground. The high carrying capacity of superconducting cable makes the magnetic flux density up to hundreds of mT around the conductor. However, the effect of high magnetic flux density on electrical tree in SiR has not been researched. In this paper, the magnetic flux density ranged from 0 to 400 mT. The electrodes were typical needle-plate electrodes. The frequency of the applied AC voltage was 50 Hz. The growth process of electrical tree was recorded by a microscope system and the pictures were taken. The experiment result indicated that the high magnetic flux density changes the tree structure and affects the growth of tree length and width.
This study proposes a method for identifying open-circuit faults in inverters using an interval sliding mode observer. The direction of current flow via the switch sets the mixed logic dynamic (MLD) model for the inverter in both normal and fault conditions. The current estimators of the upper bound sliding mode observer and the lower bound sliding mode observer are added together and weighted to construct a current interval sliding mode observer. Then, the designed observer is used to estimate the inverter's standard three-phase current. By comparing the currents recorded by the present system and the observer, the current residual can be used to discover open-circuit problems. Using the data included in the residual, a table is constructed that can be used for fault localization. The designed current interval sliding mode observer increases the robustness of fault diagnostic scheme, accelerates the convergence of interval observer, and effectively decreases chattering.
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