Innovative electrical assets are being developed in transmission and distribution, as well as in electrified transportation, from ships to aerospace. In general, power electronics have to master the ...whole power supply, being the driver of high specific power, low weight and volume components, in addition to enabling flexible and highly variable power flow. In these conditions, electrical and electronic insulation systems will have to withstand new types and levels of electric stresses, while still maintaining its reliability throughout its whole design life. This paper presents a study on the interrelation between insulating material properties and surface field of standoff insulators. The aim is mainly to provide indications on material properties which can be tailored to provide a robust, reliable and optimised insulator design that will hold for any type of electrical stress the insulation will have to withstand during operation. Specifically, we focus on ac and dc supply, including voltage transients, which could feed the same insulator depending on operation, according to a hybrid asset paradigm. The challenge is, indeed, to establish a pattern to material and insulation system design which takes into account the differences between the types of electrical stress profile and magnitude when insulators are supplied either in a dc or in ac, in order to infer which type of material characteristics would be more appropriate for the sake of life and reliability. The main contribution of this paper is to show that engineering the values of bulk and surface conductivity (which can be done selecting appropriate materials or modifying them, e.g., by nano-structuration) and modelling surface discharge inception would allow the electric field profile to be stabilised whatever the shape of the applied waveform. This will enable us to reach a reliability target that not only accounts for macroscopic phenomena, but also for the likelihood of extrinsic accelerated aging mechanism occurrence as partial discharges. In such a way, optimization of conditions to improve life, reliability, design and creepage and clearance characteristics can be achieved.
In the design of MV AC and DC spacers, the predominant factors are surface and interface conditions. Design is generally carried out on specifications and standards which are based on long-term ...experience and lab testing. However, the diffusion of power electronics with a trend to increase electric field, switching frequency, and rise time to achieve higher power density calls for an innovative, global approach to optimized insulation system design. A new methodology, based on field simulation, discharge modeling, and partial discharge inception measurements, called the three-leg approach, can form the basis to optimize insulation design for any type of supply voltage waveform. This paper focuses on the influence of the type of electrode on the inception and phenomenology of surface discharges and, as a consequence, on the interpretation of the results used for application of the three-leg approach. It is demonstrated that a typical electrode system used for insulating material testing can generate both gas and surface discharges at the triple point, when the electrodes have a smooth profile that is used to avoid corona or flashover. Hence, testing partial discharge may not provide a straightforward indication of the surface discharge inception and, thus, be partially misleading for insulation design. Another takeover is that such analysis must benefit from PD testing tools endowed with analytics able to provide automatic identification of the type of defect generating PD, i.e., internal, surface, and corona, since design and remedy actions can be taken, and adequate insulating materials developed, only knowing the type of source generating PD. Hence, testing partial discharge may not provide a straightforward indication of surface discharge inception and, thus, be partially misleading for insulation design. In addition to the importance of the three-leg approach to favor reliable and optimized design of insulation systems, there is a clear need to have a PD testing tool endowed with analytics. It should preferably be able to provide automatic identification of the type of defect generating PD, i.e., internal, surface, and corona.
The design of high voltage and medium voltage AC and DC standoff insulators, and, in general, of insulation systems where surface and interface properties are predominant factors, is based on ...specifications and standards that rely upon long‐term experiences and lab testing. Surface insulating properties depend on electrical and thermal stresses, besides environmental factors, and the inception of extrinsic ageing phenomena, such as partial discharges, can be already a cause of reduced reliability and premature failure (for organic insulating materials). An innovative approach, based on field simulation, discharge modelling, and partial discharge inception measurements is presented by the authors, which can establish a solid basis to optimise insulation design for any type of supply voltage waveform. This method, the three‐leg approach, is applied here to a cable system under AC sinusoidal voltage, but it can work for any type of insulation system, such as bushings, switch gears, transformers, rotating machines, and power electronics boards.
In electric power and electronic systems, localized breakdown of air in the form of corona, partial discharge (PD), and electrostatic discharge (ESD) occurs frequently. These processes are known to ...be sources of electromagnetic fields. Corona on overhead line conductors produces electromagnetic noise over a wide frequency range leading to electromagnetic interference. The magnetic field due to PD can be employed to detect and possibly locate PD inside the apparatus. The fields due to ESD assume importance in designing suitable protection systems. Therefore, there is a need to relate the electromagnetic field produced by the discharge phenomenon to the physical ionization process, which constitutes them. The basic mechanism behind naturally initiated electrical discharges is the electron avalanche and an expression for its total electric field has been derived and validated in the literature. The next step in this direction is to obtain the magnetic field produced by it. An expression for the complete magnetic field, i.e., both near- and far-field components, is derived starting from Lienard-Wiechert potentials. The derived expression is validated with the numerical solution of Maxwell's equation. A simplified procedure to extend avalanche results for practical discharges is demonstrated. Close agreement is obtained between the estimated results and measured results reported in the literature.
A library of non-immersive Virtual Reality (VR) tasks were developed for post-stroke rehabilitation of distal upper extremities. The objective was to evaluate the rehabilitation impact of the ...developed VR-tasks on a patient with chronic stroke. The study involved a 50-year-old male patient with chronic (13 month) stroke. Twenty VR therapy sessions of 45 min each were given. Clinical scales, cortical-excitability measures, functional MRI (fMRI), and diffusion tensor imaging (DTI) data were acquired pre-and post-therapy to evaluate the motor recovery. Increase in Fugl-Meyer Assessment (wrist/hand) by 2 units, Barthel Index by 5 units, Brunnstrom Stage by 1 unit, Addenbrooke's Cognitive Examination by 3 units, Wrist Active Range of Motion by 5° and decrease in Modified Ashworth Scale by 1 unit were observed. Ipsilesional Motor Evoked Potential (MEP) amplitude (obtained using Transcranial Magnetic Stimulation) was increased by 60.9µV with a decrease in Resting Motor Threshold (RMT) by 7%, and contralesional MEP amplitude was increased by 56.2µV with a decrease in RMT by 7%. The fMRI-derived Laterality Index of Sensorimotor Cortex increased in precentral-gyrus (from 0.28 to 0.33) and in postcentral-gyrus (from 0.07 to 0.3). The DTI-derived FA-asymmetry decreased in precentral-gyrus (from 0.029 to 0.024) and in postcentral-gyrus (from 0.027 to 0.017). Relative reduction in task-specific performance metrics, i.e., time taken to complete the task (31.6%), smoothness of trajectory (76.7%), and relative percentage error (80.7%), were observed from day 1 to day 20 of the VR therapy. VR therapy resulted in improvement in clinical outcomes in a patient with chronic stroke. The research also gives insights to further improve the overall system of rehabilitation.
Carbon dots, the nanostructures of carbon, have excellent optical and chemical properties and find a range of applications in various fields of biology and medicine. In the current study, carbon dots ...are synthesized using in vitro nonenzymatic glycosylation at 37 °C, which is the conventional method for the synthesis of Advanced Glycosylation End products. While comparing the physicochemical properties using a series of physical and chemical analyses including light absorption, fluorescence, photoluminescence, chemical composition, functional group analysis, and in vitro imaging, striking similarities are found among Carbon dots and Advanced Glycosylation End products. Based on the evident resemblance between the two, we propose either the presence of a common structural backbone or the coexistence of the two individual chemical entities. Thus, the formation of carbon dots at physiological temperatures raises health concerns as nonenzymatic glycosylation is a physiological process in humans and the rate of which is elevated during diabetes. The Advanced Glycosylation End products are known to have a detrimental effect in diabetic patients, and the chemical similarity between the two questions the widely studied biocompatibility of carbon dots.
The precise sequence of a protein’s primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of ...segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin (C) and ferrocene (F) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UVB light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F, P- b -F- b -C, and P- b -C- r -F affects the extent of the hydrophobic–hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles.
Upper extremity motor impairment is the most common sequelae in patients with stroke. Moreover, its continual nature limits the optimal functioning of patients in the activities of daily living. ...Because of the intrinsic limitations in the conventional form of rehabilitation, the rehabilitation applications have been expanded to technology-driven solutions, such as Virtual Reality and Repetitive Transcranial Magnetic Stimulation (rTMS). The motor relearning processes are influenced by variables, such as task specificity, motivation, and feedback provision, and a VR environment in the form of interactive games could provide novel and motivating customized training solutions for better post-stroke upper limb motor improvement. rTMS being a precise non-invasive brain stimulation method with good control of stimulation parameters, has the potential to facilitate neuroplasticity and hence a good recovery. Although several studies have discussed these forms of approaches and their underlying mechanisms, only a few of them have specifically summarized the synergistic applications of these paradigms. To bridge the gaps, this mini review presents recent research and focuses precisely on the applications of VR and rTMS in distal upper limb rehabilitation. It is anticipated that this article will provide a better representation of the role of VR and rTMS in distal joint upper limb rehabilitation in patients with stroke.
Transfer of bulk electric power required in the modern world can be realized only through Extra High Voltage and Ultra High Voltage transmission lines. The scenario is dominated by overhead lines in ...which electromagnetic noise generated by corona is an important concern. Corona-induced currents propagate along line conductors producing electromagnetic noise, which is essential to be quantified. Towards this end, the present work aims to investigate basic mechanism of current induction using an isolated avalanche developing under space charge modulated background field. Beginning with the complete electric field produced by an avalanche, the corresponding induced currents are quantified, and the structure of electric and magnetic fields is extracted. The well-known time-domain electric field integral equation is employed for the purpose. The basic issue with long transmission line modelling is amply demonstrated. Since single avalanche is the basic mechanism behind corona, general inferences drawn are applicable for corona on transmission lines.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The evolution of power electronics in aerospace and, in general, electrified transportation assets, is centered on the development of MV power electronics converters, which maximizes power density ...and efficiency. This turns into high-field and temperature design, ultra-fast switching, and high frequency modulation. Such conditions may pose significant and unpreceded electrothermal stresses on insulation systems of electrical asset components, such as printed circuit boards. Magnitude, profile and time behavior of stresses, as well as their effect on intrinsic and extrinsic aging mechanisms, have to be known, being the basis of a highly-reliable electrothermal insulation design able to provide a specified life at specified failure probability. This paper introduces innovative criteria to optimize the design of insulation system of MV PCB, according to the new "three-leg" approach that consists of interlacing electric field simulation, life and discharge modelling, and partial discharge testing. The essence of such an approach is to design an insulation system, as regards bulk and surface sub-components, by a global view, where aging processes rule design rather than macroscopic failure risk. Accordingly, life and reliability are determined by appropriate models, accounting for intrinsic aging and, in addition, design ensures that operation stresses do not trigger extrinsic accelerated aging mechanisms, as those associated to partial discharges. It is shown in the paper that the proposed approach can lead to an innovative and effective design, delivering the specified life and ensuring that the electrical field on the surface (and in the bulk) is limited to values below the threshold for partial discharge inception. This can question, in principle, the use of creepage and clearance tools, since the new design procedure will be related to the minimization of likelihood of partial discharge inception, rather than to avoid the risk of macroscopic surface discharges.
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