Application of Molecular Sieves for Drying Transformers Insulated with Mineral Oil, Natural Ester, or Synthetic Ester

A high level of moisture in the insulation system of power transformers is often the cause of their failure. This can be prevented by drying a transformer in its place of installation. In the article the application of molecular sieves (MS) in the drying process of the transformer insulation system was analyzed. The water sorption isotherms of 3A MS in mineral oil, natural ester, and synthetic ester at 35 °C were determined, which was not described in the literature before. An evaluation of the influence of temperature on the drying dynamics of electro-insulating liquids using MS was also carried out. The drying dynamics were tested at three temperatures, i.e., 35 °C, 50 °C, and 65 °C, which allowed to analyze the effect of temperature on a short-term or continuous drying process. The tests showed that 3A MS’s ability to adsorb water varied depending on the type of electro-insulating liquid. The determined water sorption isotherms, described by means of Langmuir adsorption model, make it possible to calculate the amount of MS needed for drying transformers with different liquid insulation. The research and analyses show the MS’s great potential for the drying of transformer insulation systems.

Use of maltodextrin and gum arabic for encapsulation of red cabbage anthocyanins

Maltodextrin (MD) and two types of gum arabic (IRX 40642 and IRX 49345) were used to encapsulate anthocyanins of red cabbage. The solution of the encapsulated dye was evaluated by polarized light microscopy. The spray-dried powder (microspheres) containg anthocyanins (red cabbage juice obtained by disintegration and filtration) and encapsulating agent was characterized by Scanning Electron Microscopy (SEM) and water sorption isotherms; the product color characterization was measured using software of imaging analysis (Mathematica). The microspheres showed that in gum arabic solutions, the dye was located at the wall. Specifically, dried gum arabic microspheres had a better quality than that produced by the maltodextrin because the MD does not form microsphere, but serving only as wall material. GAB isotherm was well fitted on experimental water sorption data. Through the color parameters quantified in CIELab and CIELCH systems for anthocyanin solutions in the presence of three studied encapsulating agents, it was possible to observe that maltodextrin had little effect on the coloring of the dye solution, for example, through the analysis of the hue parameter H, which was least affected by changes in concentration or pH from 5.0 to 3.0. The gum arabic IRX 40642 showed an oxidized hue, while gum arabic IRX 49345 gave similar colors to the original dye at concentrations less or equal to 10%. Even with some limitations, it was concluded that the gums used in this study are suitable for the encapsulation of red cabbage anthocyanins.