SSIMS Molecular Selective Imaging: a new diagnostic tool to investigate metal passivators in scrapped transformers

In every high voltage grid, the replacement of assets is a slow but steady process that guarantees long-term reliability of the power distribution networks. The prioritisation of such interventions is based on complex rating criteria specifically designed to highlight potential issues of certain machines (or families of machines) in need of care. Given the tremendous costs of operations such as the replacement of a power transformer it is not surprising to observe constant efforts devoted to finding new and better monitoring and diagnostic tools. These are capable of delivering invaluable information about the conditions of a transformer, in service or after it is either failed or proactively scrapped, allowing a better comprehension of underlying chemical-physical phenomena occurring. Ideally, advanced monitoring and diagnostic tools should ultimately result in improved rating parameters to be applied in the evaluation of future interventions. This feasibility study evaluates the use of static secondary ion mass spectrometry (SSIMS) molecular selective imaging as a diagnostic tool for power transformer. SSIMS is herein demonstrated to be able to assess, without doubts, the presence and integrity of the passivation layer produced by Irgamet®39 on copper surfaces in laboratory tests. The technique has also been tested on real samples collected from one of the phases of a 400/275kV autotransformer proactively scrapped and proved to be applicable without significant sample preparation. The possibility of its use in the study of the distribution of Irgamet®39 across the windings is also demonstrated. Further development of SSIMS as a diagnostic tool would be significantly increasing the grade of detail at which scrapped/failed units could be inspected. A better understanding on how the operating conditions or the design of a transformer can affect the anticorrosion protection layer at the molecular level would open the way to significant ad hoc improvements of both operative guidelines and rating criteria for power transformers

Tracking the progression of sulfur corrosion in transformer oil using thin film sacrificial copper strip

In this work, thin film sacrificial copper strips are introduced as sensors to provide a direct indication on the corrosiveness of insulating oils. The progression of sulfur corrosion in transformer insulating oils was simulated by adding different concentrations of dibenzyl disulfide into glass Petri dishes, each containing 40 mL of non-corrosive oil. The resistive thin film copper strips were deposited onto a glass substrate using an electron beam evaporator and the strips were then immersed into the corrosive oil samples. The samples were aged in a forced convection laboratory oven at 130 °C for 20 h. The material loss due to the presence of corrosive compounds was monitored by measuring the resistance of the thin film copper strips using four-wire resistance measurements. The preliminary results reveal that the corrosive by-products (due to the breakdown of dibenzyl disulfide) accelerates the corrosion of the thin film copper strips, as evidenced from the amount of copper loss on the surface of the strips. This increases the resistance values of the thin film copper strips. Based on the variations in the resistance of the thin film copper strips, one can infer the level of sulfur corrosion in transformer insulating oils.</p

Sacrificial copper strip sensors for sulfur corrosion detection in transformer oils

Existing protocols (e.g., ASTM D 1275-B standard test method) applied to detect and monitor sulfur corrosion in transformer insulating oils are imprecise as it depends on visual observation. As a solution, thin-film sacrificial copper strips are proposed as a corrosive sulfur sensor. A two-level factorial design is utilized to investigate the significant effect of area and thickness upon the sensor's transformation resistance values. Next, a regression model is developed to estimate the sensor's transformation resistance values as functions of area and thickness. The resultant outputs from the two-level factorial design revealed that area, as a variable, exhibited higher significance at 90.19%, compared to either thickness or interaction between area and thickness. The proposed regression model obtained from two-level factorial design is significant in describing the trend displayed by the sensor's transformation resistance values. Finally, this paper details the clear correlation between the sensor's transformation resistance values and elemental sulfur concentration.</p

Stereocontrolled synthesis of (-)-galanthamine

An enantioselective synthesis of (-)-galanthamine has been realized in 11 linear steps starting from isovanillin. A Mitsunobu aryl ether forming reaction was used to assemble the galanthamine backbone, which was stitched together using enyne ring-closing metathesis, Heck, and N-alkylation reactions affording the tetracyclic ring system. Control of relative and absolute stereochemistry was derived from an easily accessible enantiomerically enriched propargylic alcohol 13

Analytical theory of gamma-encoded double-quantum recoupling sequences in solid-state nuclear magnetic resonance

Many important double-quantum recoupling techniques in solid-state NMR are classified as being ?-encoded. This means that the phase of the double-quantum effective Hamiltonian, but not its amplitude, depends on the third Euler angle defining the orientation of the molecular spin system in the frame of the magic-angle-spinning rotor. In this paper, we provide closed analytical solutions for the dependence of the powder-average double-quantum-filtered signal on the recoupling times, within the average Hamiltonian approximation for ?-encoded pulse sequences. The validity of the analytical solutions is tested by numerical simulations. The internuclear distance in a 13C2-labelled retinal is estimated by fitting the analytical curves to experimental double-quantum data

X-ray fluorescence as a condition monitoring tool for copper and corrosive sulphur species in insulating oil

Currently there are no standard techniques to detect copper sulphide deposits in transformers to act as an early warning system. This paper develops and tests a procedure using X-Ray Fluorescence (XRF) spectroscopy to tackle this problem and to monitor dissolved copper in oil, which can have a major impact on the dielectric properties of insulating oil. Initially calibration curves for sulphur and copper demonstrate the XRF’s limits of quantitation. Subsequently, a laboratory scale sample preparation procedure is developed to demonstrate that corrosive sulphur depletion trends may indirectly monitor copper sulphide formation. To confirm depleting sulphur species are corroding copper samples are analysed with Energy Dispersive X-Ray spectroscopy. Finally XRF demonstrates that corrosive oil has a low impact on the long term concentration of copper in oil. An XRF condition monitoring technique feasibility study is conducted and recommendations are given in how to implement it in the field

Unicoloniality, recognition and genetic differentiation in a native Formica ant.

Some ants have an extraordinary form of social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This mode of social organization has been primarily studied in introduced and invasive ant species, so that the recognition ability and genetic structure of ants forming unicolonial populations in their native range remain poorly known. We investigated the pattern of aggression and the genetic structure of six unicolonial populations of the ant Formica paralugubris at four hierarchical levels: within nests, among nests within the same population, among nests of populations within the Alps or Jura Mountains and among nests of the two mountain ranges. Ants within populations showed no aggressive behaviour, but recognized nonnestmates as shown by longer antennation bouts. Overall, the level of aggression increased with geographic and genetic distance but was always considerably lower than between species. No distinct behavioural supercolony boundaries were found. Our study provides evidence that unicoloniality can be maintained in noninvasive ants despite significant genetic differentiation and the ability to discriminate between nestmates and nonnestmates

Structure-Based Optimization of Nonquaternary Reactivators of Acetylcholinesterase Inhibited by Organophosphorus Nerve Agents

International audienceAcetylcholinesterase (AChE), a key enzyme in the central and peripheral nervous systems, is the principal target of organophosphorus nerve agents. Quaternary oximes can regenerate AChE activity by displacing the phosphyl group of the nerve agent from the active site, but they are poorly distributed in the central nervous system. A promising reactivator based on tetrahydroacridine linked to a nonquaternary oxime is also an undesired submicromolar reversible inhibitor of AChE. X-ray structures and molecular docking indicate that structural modification of the tetrahydroacridine might decrease inhibition without affecting reactivation. The chlorinated derivative was synthesized and, in line with the prediction, displayed a 10-fold decrease in inhibition but no significant decrease in reactivation efficiency. X-ray structures with the derivative rationalize this outcome. We thus show that rational design based on structural studies permits the refinement of new-generation pyridine aldoxime reactivators that may be more effective in the treatment of nerve agent intoxication