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In on-site measurement, as the transformer’s structure is often unknown, the application of frequency domain spectroscopy (FDS) is greatly limited in moisture assessment of transformer. This paper proposes a moisture assessment method for oil-immersed paper based on the dynamic characteristic frequency even for an unknown transformer structure. FDS tests are performed on the oil-paper insulation, corresponding oil-immersed paper, and mineral oil under different moisture conditions. The moisture criterion of oil-immersed paper and the influence of the structural parameters on the calculated frequency spectroscopy at different frequencies are discussed. It is concluded that the moisture criterion’s effectiveness, which indicates the sensitivity of assessed moisture content to the error of the tan $\delta $ , changes at different frequencies. Moreover, there are some frequencies at which tan $\delta $ is not influenced by structural parameters and is close to the measured value, which are regarded as “characteristic frequencies.” Based on the characteristic frequency, the moisture content of oil-immersed paper is assessed according to the frequency spectroscopy of oil-paper insulation without the structural parameters. The result shows that the assessing frequency changes under different moisture conditions, and the error of the assessed moisture content is less than 0.1%.

Metal wire mesh is widely used in the energy industry for its excellent protective properties as a fire stopping and explosion isolating material. In this study, the suppression characteristics of different layers of metal mesh on the dynamic behavior of premixed methane-air flame propagation were studied experimentally. A high-speed photographic schlieren system was used to photograph the explosion process to capture the changes in the microstructure of the flame, and high-frequency pressure sensors and micro-thermocouple measurements were used to capture the flame explosion pressure and temperature. The experimental results show that the suppression effectiveness of wire mesh is a reflection of the coupling of explosive flame propagation behavior and combustion state in the pipe. Increasing the number of mesh layers and mesh density can destroy the microstructure of the premixed methane-air flame front and hinder the progress of flame propagation. Increasing the number of wire mesh layers will delay the peak time of premixed flame propagation speed and reduce the peak speed values of flame propagation. Wire mesh has a pronounced attenuation effect on premixed flame temperature and explosion overpressure. The maximum flame temperature attenuation rate is 34.99%–60.95%, and the maximum explosion overpressure attenuation rate is 33.70%–74.02%. And the suppression effect is greatly enhanced as the increase of mesh layers.

In this study, an efficient and simple nanocomposite was designed for detection of uric acid (UA). This nanocomposite is composed of titanium-potassium niobate (K3Ti5NbO14) and 5, 10, 15, 20-tetrakis (N-methylpyridinium-4-yl) porphyrinato iron (III) (FeTMPyP) through a simple exfoliation/reassembling method by means of electrostatic self-assembly technology. The change of morphology and structure has been verified by the characterization means of scanning electron micrograph, energy-dispersive spectroscopy, transmission electron microscope, high-resolution transmission electron microscope, X-ray powder diffraction, and fourier transform infrared spectroscopy. Furthermore, electrochemical measurements demonstrated that FeTMPyP/Ti5NbO14 composite has improved the electrochemical oxidation effect on UA due to its improved electron transfer properties and the FeTMPyP/Ti5NbO14 modified electrode has a low detection limit of 0.5 µM with the concentration range from 2.5 to 382 µM. Further investigation proved that FeTMPyP/Ti5NbO14 composite has satisfactory stability, good reproducibility, and strong antiinterference property, and has great application value in the detection of UA. [ABSTRACT FROM AUTHOR]