The Experts below are selected from a list of 5178 Experts worldwide ranked by ideXlab platform
Ires Iskender - One of the best experts on this subject based on the ideXlab platform.
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electromagnetic force investigation on distribution transformer under unbalanced faults based on time stepping finite element methods
International Journal of Electrical Power & Energy Systems, 2016Co-Authors: Atabak Najafi, Ires IskenderAbstract:Abstract The occurrence of Short Circuit faults is a major cause behind the windings deformation in the transformers. Mechanical force is proportional to the square of the current. Hence under Short Circuit Condition, it will be very high. These stresses radially or axially affect the transformer windings. Therefore, in the transformer designing, evaluating the effects of Short-Circuit current and inrush current is very important. In this paper, 2-D and 3-D time stepping finite element methods (TSFEM) that improved in Ansoft-Maxwell, are utilized as Instruments to investigate the leakage flux and electromagnetic forces due to Short Circuit and inrush current on the windings of 1000 kV A, 10/0.4 kV three-phase, three leg, distribution transformer. Electromagnetic forces in the transformer windings are produced as a result of combination between the current density and the leakage flux density in the winding regions. The study demonstrates that, especially, under single phase-to-ground Short Circuit fault, leakage flux density on the windings of transformer remarkably increase. The interaction between this high leakage flux with current density, causes the significant increase in the electromagnetic forces in transformer windings.
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A new approach to reduce the leakage flux and electromagnetic force on distribution transformer under unbalanced faults based on finite element method
International Transactions on Electrical Energy Systems, 2015Co-Authors: Atabak Najafi, Ires IskenderAbstract:Summary The Short-Circuit capacity design of a transformer is one of the most significant and challenging criteria. Electromagnetic forces in transformer winding regions are produced by interaction between the leakage flux and current density. Under Short Circuit Condition when currents increase to 20 times, windings are exposed to very high electromagnetic force. This paper is focused on the reduction of leakage flux and electromagnetic force under fault Condition of distribution transformer. This article is composed of two parts. First, Finite Element Methods (FEM) that improved in Ansoft-Maxwell has been used to investigate the leakage flux and electromagnetic forces of three-phase, three leg, 10/0.4-kV, 1000-kVA distribution transformer. Then, to optimal design of transformer under single phase to ground Short Circuit Condition two auxiliary winding was chosen as an active shielding to reduce the radial and axial leakage flux. According to Lenz's law this windings produce a magnetic flux that is the apposite of the leakage flux from an iron-core system. Results indicate that the proposed auxiliary winding remarkably decreased the leakage flux and electromagnetic force in the winding regions. It should be noted that the resultant of main flux is not affected by auxiliary winding. Copyright © 2015 John Wiley & Sons, Ltd.
Paul R Berger - One of the best experts on this subject based on the ideXlab platform.
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plasmon enhanced optical absorption and photocurrent in organic bulk heterojunction photovoltaic devices using self assembled layer of silver nanoparticles
Solar Energy Materials and Solar Cells, 2010Co-Authors: Woojun Yoon, Kyungyoung Jung, Jiwen Liu, Thirumalai Duraisamy, Rao Revur, Fernando L Teixeira, S Sengupta, Paul R BergerAbstract:Abstract Improved optical absorption and photocurrent for polythiophene–fullerene bulk heterojunction photovoltaic devices is demonstrated using a unique self-assembled monolayer of Ag nanoparticles formed from a colloidal solution. With the presence of suitable nanoparticle organic capping groups that inhibit its propensity to agglomerate, the particle-to-particle spacing can be tailored. Transmission electron microscopy reveals the self-assembled Ag nanospheres are highly uniform with an average diameter of ∼4 nm and controllable particle-to-particle spacing. The localized surface plasmon resonance peak is ∼465 nm with a narrow full width at half maximum (95 nm). In the spectral range of 350–650 nm, where the organic bulk heterojunction photoactive film absorbs, an enhanced optical absorption is observed due to the increased electric field in the photoactive layer by excited localized surface plasmons within the Ag nanospheres. Under the Short-Circuit Condition, the induced photo-current efficiency (IPCE) measurement demonstrates that the maximum IPCE increased to ∼51.6% at 500 nm for the experimental devices with the self-assembled layer of Ag nanoparticles, while the IPCE of the reference devices without the plasmon-active Ag nanoparticles is ∼45.7% at 480 nm. For the experimental devices under air mass 1.5 global filtered illuminations with incident intensity of 100 mW/cm2, the increased Short-Circuit current density is observed due to the enhancement of the photogeneration of excitons near the plasmon resonance of the Ag nanoparticles.
Michael F Durstock - One of the best experts on this subject based on the ideXlab platform.
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in situ characterization of lifetime and morphology in operating bulk heterojunction organic photovoltaic devices by impedance spectroscopy
Advanced Energy Materials, 2012Co-Authors: Benjamin J Leever, Christopher Bailey, Tobin J Marks, Mark C Hersam, Michael F DurstockAbstract:Time-dependent charge transport in operating poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction organic photovoltaic (OPV) devices has been characterized with impedance spectroscopy. Devices with varied composition and morphology were measured over a range of illumination intensities ranging from dark Conditions to 1 sun and applied bias voltages ranging from 0.0 V to 0.75 V. Using an equivalent Circuit model, materials properties such as dielectric constant and conductivity were determined and found to be in agreement with values measured by other methods. Average carrier lifetimes were also extracted from the model and found to correlate with measured power conversion efficiencies. At the Short Circuit Condition and ∼1 sun illumination, the average electron lifetime was found to vary from 7.8 to 22 μs for devices with power conversion efficiencies ranging from 2.0 to 2.5%. These results suggest that impedance spectroscopy is an effective tool for predicting how processing parameters can impact device performance in organic bulk heterojunction photovoltaic devices.
Atabak Najafi - One of the best experts on this subject based on the ideXlab platform.
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electromagnetic force investigation on distribution transformer under unbalanced faults based on time stepping finite element methods
International Journal of Electrical Power & Energy Systems, 2016Co-Authors: Atabak Najafi, Ires IskenderAbstract:Abstract The occurrence of Short Circuit faults is a major cause behind the windings deformation in the transformers. Mechanical force is proportional to the square of the current. Hence under Short Circuit Condition, it will be very high. These stresses radially or axially affect the transformer windings. Therefore, in the transformer designing, evaluating the effects of Short-Circuit current and inrush current is very important. In this paper, 2-D and 3-D time stepping finite element methods (TSFEM) that improved in Ansoft-Maxwell, are utilized as Instruments to investigate the leakage flux and electromagnetic forces due to Short Circuit and inrush current on the windings of 1000 kV A, 10/0.4 kV three-phase, three leg, distribution transformer. Electromagnetic forces in the transformer windings are produced as a result of combination between the current density and the leakage flux density in the winding regions. The study demonstrates that, especially, under single phase-to-ground Short Circuit fault, leakage flux density on the windings of transformer remarkably increase. The interaction between this high leakage flux with current density, causes the significant increase in the electromagnetic forces in transformer windings.
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A new approach to reduce the leakage flux and electromagnetic force on distribution transformer under unbalanced faults based on finite element method
International Transactions on Electrical Energy Systems, 2015Co-Authors: Atabak Najafi, Ires IskenderAbstract:Summary The Short-Circuit capacity design of a transformer is one of the most significant and challenging criteria. Electromagnetic forces in transformer winding regions are produced by interaction between the leakage flux and current density. Under Short Circuit Condition when currents increase to 20 times, windings are exposed to very high electromagnetic force. This paper is focused on the reduction of leakage flux and electromagnetic force under fault Condition of distribution transformer. This article is composed of two parts. First, Finite Element Methods (FEM) that improved in Ansoft-Maxwell has been used to investigate the leakage flux and electromagnetic forces of three-phase, three leg, 10/0.4-kV, 1000-kVA distribution transformer. Then, to optimal design of transformer under single phase to ground Short Circuit Condition two auxiliary winding was chosen as an active shielding to reduce the radial and axial leakage flux. According to Lenz's law this windings produce a magnetic flux that is the apposite of the leakage flux from an iron-core system. Results indicate that the proposed auxiliary winding remarkably decreased the leakage flux and electromagnetic force in the winding regions. It should be noted that the resultant of main flux is not affected by auxiliary winding. Copyright © 2015 John Wiley & Sons, Ltd.
Bernard Kippelen - One of the best experts on this subject based on the ideXlab platform.
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efficient thin film organic solar cells based on pentacene c60 heterojunctions
Applied Physics Letters, 2004Co-Authors: Benoit Domercq, Bernard KippelenAbstract:We have fabricated an efficient organic photovoltaic cell based on a heterojunction of pentacene and C60. Photocurrent action spectra exhibit broad light-harvesting throughout the visible spectrum with a peak external quantum efficiency (EQE) of 58±4% at Short-Circuit Condition. Modeling studies indicate that this high EQE can be partly attributed to the large exciton diffusion length in the pentacene film as well as efficient dissociation of excitons at the pentacene/C60 heterojunction.