Insight into the dielectric response of transformer oil-based nanofluids

The oil-based nanofluids with greater dielectric strength have attracted much attention as a crucial insulating materials in high-voltage oil-immersed power equipment. In fact, the different microstructures of the transformer oil-based nanofluids (TNFs) would result in different dielectric properties. In this work, the broadband dielectric spectroscopy measurement was used to establish the linkage between the electric double layer (EDL) and dielectric response properties of TNFs which was performed at 298K temperature and with frequency range from 10-2Hz∼106Hz. The modified Havriliak-Negami (HN) model function was used to analyze the measured results. The results demonstrate that both the real and imaginary parts of dielectric spectra of two kinds of oil are composed of the conductivity and polarization process. Compared with pure oil, two polarization process could be observed for the TNFs, explained by the EDL structure reasonably. The introduction of the EDL structure provides an idea to account for the insulating strength improvement of TNFs for the first time

Theoretical connection from the dielectric constant of films to the capacitance of capacitors under high temperature

In the process of coping with energy and environmental protection issues, technologies such as energy materials, energy devices, and energy systems have made great progress. With excellent performance, film capacitors play an increasingly important role in energy-related fields. With the increase of application scenarios and the continuous development of film material technology, it is urgent to establish a better theoretical connection from films to capacitors. First, the main components of the capacitor including the film and the positional relationships among them are given. Then, from the two perspectives of indirect calculation according to the volume and the direct calculation according to the winding process, the equation between the dielectric constant of films and the corresponding capacitance of capacitors is established. Further, the measurement data and error analysis results of the built test platform prove the accuracy and great potential of the proposed calculation methods. In addition, error sources, including film thickness uniformity, are listed. Finally, the challenges faced by the proposed calculation methods and the paths that can be referenced for future research are summarised and discussed.</p

Physical Properties of H II Regions in M51 from Spectroscopic Observations

M51 and NGC 5195 is an interacting system that can be explored in great details with ground-based telescopes. The H II regions in M51 were observed using the 2.16 m telescope of the National Astronomical Observatories of the Chinese Academy of Sciences and the 6.5 m Multiple Mirror Telescope with spatial resolution of less than $\sim100$ pc. We obtain a total of 113 spectra across the galaxy and combine the literature data of Croxall et al. to derive a series of physical properties, including the gas-phase extinction, stellar population age, star formation rate (SFR) surface density, and oxygen abundance. The spatial distributions and radial profiles of these properties are investigated in order to study the characteristics of M51 and the clues to the formation and evolution of this galaxy. M51 presents a mild radial extinction gradient. The lower gas-phase extinction in the north spiral arms compared to the south arms are possibly caused by the past encounters with the companion galaxy of NGC 5195. A number of H II regions have the stellar age between 50 and 500 Myr, consistent with the recent interaction history by simulations in the literatures. The SFR surface density presents a mild radial gradient, which is ubiquitous in spiral galaxies. There is a negative metallicity gradient of $-0.08$ dex $R_{e}^{-1}$ in the disk region, which is also commonly found in many spiral galaxies. It is supported by the "inside-out" scenario of galaxy formation. We find a positive abundance gradient of 0.26 dex $R_{e}^{-1}$ in the inner region. There are possible reasons causing the positive gradient, including the freezing of the chemical enrichment due to the star-forming quenching in the bulge and the gas infall and dilution due to the pseudobulge growth and/or galactic interaction.Comment: 20 pages, 8 figures, 1 appendix, Accepted for publication in PASP. Comments and suggestions are welcom

The influence of TiO₂ nanoparticle incorporation on surface potential decay of corona-resistant polyimide nanocomposite films

PI nanocomposite films containing surface modified nanoparticles by employing silane coupling agent were prepared using in-situ dispersion polymerization process. The surface potential decay measurements on films were investigated over the different negative corona-charged voltages and times in a controlled environment where temperature and relative humidity were kept at 21 ºC and 45%, respectively. There is a significant change in the surface potential decay characteristics after nano-fillers were introduced into polyimide. The surface potential decay pattern depends also on the amount of nano-fillers. The possible surface potential decay and corona resistance mechanisms responsible for the observed phenomena were discussed