Search

Partial dampness is the initial stage in the bushing damp process,so the effective diagnosis of partial dampness can avoid the further development of the damp. The partial damp diagnosis method of bushing based on the frequency domain spectroscopy (FDS) is proposed in this paper. Firstly,oil-paper insulation samples with different moisture content are prepared,and partial damped samples are formed through combination. Then the FDS characteristics are obtained. The results show that partial distribution of moisture leads to oil-paper insulation interfaces with different moisture content,and the interface relaxation polarization loss peak is introduced in the FDS curves. The greater the degree of partial dampness in the radial direction,the greater the amplitude of the loss peak,and it moves to the high frequency direction. The effectiveness of the diagnosis of partial dampness of bushing based on the characteristics of the interface relaxation polarization loss peak is verified by the simulation model of the transformer bushing. It shows that a new method for early fault warning and diagnosis of the transformer bushing is provided.

Due to long-term exposure to high electrical field strength, heavy loads, and the complex climatic conditions in tropical coastal areas of China, widespread abnormal heating phenomena often occur in the operation of composite insulators in power transmission lines, posing a threat to the safe and stable operation of the power system. To study the ageing process of the silicone rubber sheath of composite insulators in the high-field, high-humidity, high-temperature, and high-salt-density environments along the coastal regions, this paper establishes a humidity–heat–electricity–salt spray accelerated ageing test platform and conducts ageing tests on silicone rubber materials for composite insulators under the coupled effect of multiple factors. The ageing characteristics of silicone rubber materials are analyzed using scanning electron microscopy, Fourier infrared spectroscopy, thermogravimetric analysis, and other methods. The results show that the coupled ageing factors have an impact on the surface morphology of silicone rubber. The continuous depolymerization of PDMS molecular chains leads to a decrease in the content of groups related to the hydrophobicity of the material, resulting in a deterioration of its hydrophobicity. Moreover, the degradation of silicone rubber materials and the enhanced moisture absorption capacity lead to an increase in the dielectric loss tangent of the saturated moisture-absorbing medium, thereby causing abnormal heating of the sheath at the end of the composite insulator. The research findings of this study are of significant reference value for revealing the degradation mechanism of composite insulator silicone rubber sheaths in tropical island environments and improving the service life of composite insulators. [ABSTRACT FROM AUTHOR]

Herein, we report an effective surface modification for a high energy cathode material, LiNi0.6Co0.2Mn0.2O2 (NCM-622), using an Al-based MOF (NH2-MIL-53), as a precursor to produce MOF-derived alumina (MDA) coatings. The MDA-coating (2.5 wt%) is well-dispersed on the surface of NCM-622 with an amorphous structure. By virtue of the MDA-coating, NCM-622 shows greatly enhanced electrochemical performance: 214.6 mA h g−1 and 196.5 mA h g−1 (3.0–4.5 V vs. Li+/Li) at 0.2C and 1C, respectively, with a capacity retention of 92.7% after 100 cycles at 1C; even at high rates of 5C and 10C, the discharge capacity still approaches 168.5 mA h g−1 and 150.0 mA h g−1, respectively. We found that these enhancements can be ascribed to the improved structural stability and electrochemical kinetics of NCM-622 by the MDA-coating. [ABSTRACT FROM AUTHOR]

Due to size-dependent catalytic selectivity, the size and special morphology are of great importance to applications of TiO2. The synthesis method of size and morphology control has been in need of innovation. In this study, TiO2 nanoparticles(TiO2-NPs) with well-defined morphology and homogenous size were synthesized using a novel method, in which bamboo substrate, dielectrophoresis (DEP) technology and a sol-gel process were combined(substrate/ DEP/ sol-gel). Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the TiO2-NPs. Further study showed that, with this combined method, the size and the uniformity of TiO2-NPs can be controlled by changing the voltage of DEP. The number and arrangement of TiO2 nanorods can be controlled by changing the voltage. Substrate/ DEP/ sol-gel proved to be an efficient way to form special morphologies of TiO2-NPs. A visible-light catalytic activity experiment showed that among three preparation methods, the substrate/ DEP/ sol-gel method made TiO2-NPs with the highest catalytic activity for degradation of methyl orange. TiO2-NPs produced by the DEP/ sol-gel process presented higher catalytic activity than TiO2-NPs produced by only a sol-gel process. [ABSTRACT FROM AUTHOR]

A mechanochemical synthetic method of preparing LiCoO2 coated by MOF-derived metal oxide composites is introduced. Mono-dispersed ZrO2 and Al2O3 are applied as protection layers. These composites show 148 mA h g−1 at a current density of 2325 mA g−1 and excellent thermal stability (55 °C). [ABSTRACT FROM AUTHOR]

A thin layer of a highly porous metal-organic framework material, ZIF-8, is fabricated uniformly on the surface of nanostructured transition metal oxides (ZnO nanoflakes and MnO 2 nanorods) to boost the transfer of lithium ions. The novel design and uniform microstructure of the MOF-coated TMOs (ZIF-8@TMOs) exhibit dramatically enhanced rate and cycling performance comparing to their pristine counterparts. The capacities of ZIF-8@ZnO (nanoflakes) and ZIF-8@MnO 2 (nanorods) are 28 % and 31 % higher that of the pristine ones at the same current density. The nanorods of ZIF-8@MnO 2 show a capacity of 1067 mAh g -1 after 500 cycles at 1 Ag -1 and without any fading. To further improve the conductivity and capacity, the ZIF-8-coated materials are pyrolyzed at 700 °C in an N 2 atmosphere (ZIF-8@TMO-700 N). After pyrolysis, a much higher capacity improvement is achieved: ZIF-8@ZnO-700 N and ZIF-8@MnO 2 -700 N have 54 % and 69 % capacity increases compared with the pristine TMOs, and at 1 Ag -1 , the capacity of ZIF-8@MnO 2 -700 N is 1060 mAh g -1 after cycling for 300 cycles., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)