Hydrogen gas generation due to moderately overheated transformer cores
This paper first presents an overview of this phenomenon from its initial discovery to the stage of the factory/laboratory investigations performed to confirm this new mechanism of gas generat ion in power transformers. This is followed by an overview of the increased significance of developing accurate calculation of the core hot spot temperature. The paper then presents the detailed accurate diagnosis performed on a 600 MVA transformer that had this issue in the field, the improvement made, and the calculation of the predicted gas generation performance of its loading cycle throughout a year of operation. The paper then presents the basis for the additions/changes proposed to be implemented in the IEEE Standards as a result of the discovery of this new gas generation mechanism. The paper also provides the basis for recommending to the IEEE Standards the selection of 130°C as the allowed maximum core hot spot temperature under sustained worst conditions of load, core — excitation and ambient temperature.
Production mechanism of single excessive hydrogen in current transformers: A reactive molecular dynamics simulation study
Abstract The present work aims at investigating the single excessive hydrogen (SEH) mechanism in the current transformers (CTs) by reactive force field molecular dynamics (ReaxFF MD) simulations. The chemical components in the CTs, i.e. mineral insulating oil, insulating paper, nickel crystal and moisture were established. Temporal evolutions of dissolved-gas-analysis (DGA) characteristic gases were captured reasonably in the mono-component, dual-component and multi-component simulation systems under electrical stress. And the sources of H2 molecules were traced as well as their dehydrogenation reactions. In addition, the oil chromatogram and dismantle experiments were performed to verify the dynamics simulations. The relative contents of the gas productions in the all-component composite simulation system were well agreed to that from oil chromatogram measurement. The results identified that the nickel-catalyse dehydrogenation from insulating oil played the dominant role in SEH phenomenon. The Nickel promoted the generation of H2 by seizing H atoms from oil molecules under the imposed electric field. In the process of dehydrogenation, the insulating oil molecules reacted to produce macromolecule wax-like solid unsaturated hydrocarbons, which were found in the insulating paper of a dismantled CT.
The peculiar thermo-structural behavior of the anionic lipid DMPG.
Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing. Structural properties of the DMPG gel-fluid transition region will be discussed, based on results obtained by several techniques: electron spin resonance (ESR) of spin labels at the membrane surface and intercalated at different depths in the bilayer; light scattering; DSC; small angle X-ray scattering (SAXS); and fluorescence spectroscopy of probes in the bilayer.