The Experts below are selected from a list of 29277 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.
Zuhre şenturk - One of the best experts on this subject based on the ideXlab platform.
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electrochemical determination of pterostilbene at a cathodically pretreated boron doped diamond electrode using square wave adsorptive anodic stripping voltammetry in cationic surfactant media
Sensors and Actuators B-chemical, 2016Co-Authors: Aydin Yigit, Yavuz Yardim, Ozlem Selcuk Zorer, Zuhre şenturkAbstract:Abstract In the present paper, an electrochemical method was developed for the determination of pterostilbene (a phenolic phytoalexin) using adsorptive anodic stripping voltammetry at a cathodically pretreated boron-doped diamond electrode. The oxidation of compound was irreversible and exhibited an adsorption controlled process which is of pH dependence. The sensitivity of the stripping voltammetric measurements was significantly improved in the presence of cationic surfactant, cetyltrimethylammonium bromide (CTAB). Using square-wave stripping mode, a highly linear analytical curve was obtained for pterostilbene determination in 0.1 M HNO3 solution containing 2 × 10−4 M CTAB at +0.78 V (vs. Ag/AgCl) (after 30 s accumulation at open-Circuit Condition). The process could be used in the range of 0.005–1.0 μg mL−1 (2.0 × 10−8–3.9 × 10−6 M), with a detection limit of 0.0011 μg mL−1 (4.3 × 10−9 M). The proposed method was successfully applied to measure the concentration of pterostilbene in the commercial dietary supplements, with results similar to those obtained using a HPLC method at 95% confidence level. As far as it could be verified, the proposed method is the first one based on the electrochemical investigation of pterostilbene.
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determination of vanillin in commercial food product by adsorptive stripping voltammetry using a boron doped diamond electrode
Food Chemistry, 2013Co-Authors: Yavuz Yardim, Mehmet Gulcan, Zuhre şenturkAbstract:Abstract A method for the determination of food additive vanillin was developed by adsorptive stripping voltammetry. Its determination was carried out at the anodically pre-treated boron-doped diamond electrode in aqueous solutions. Using square-wave stripping mode, the compound yielded a well-defined voltammetric response in phosphate buffer, pH 2.5 at +1.14 V (vs. Ag/AgCl) (a pre-concentration step being carried out at open-Circuit Condition for 60 s). A linear calibration graph was obtained in the concentration range of 0.5–15.0 μg mL −1 (3.3 × 10 −6 –9.8 × 10 −5 mol L −1 ) with a detection limit of 0.024 μg mL −1 (1.6 × 10 −7 mol L −1 ). As an example, the practical applicability of the proposed method was tested for the determination of this flavouring agent in commercial pudding powder of Keshkule (Turkish milk pudding with almond flour).
Olle Inganas - One of the best experts on this subject based on the ideXlab platform.
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semi transparent tandem organic solar cells with 90 internal quantum efficiency
Advanced Energy Materials, 2012Co-Authors: Zheng Tang, Zandra George, Jonas Bergqvist, Kristofer Tvingstedt, Koen Vandewal, Ergang Wang, Mattias L Andersson, Mats Andersson, Fengling Zhang, Olle InganasAbstract:Semi-transparent (ST) organic solar cells with potential application as power generating windows are studied. The main challenge is to find proper transparent electrodes with desired electrical and optical properties. In this work, this is addressed by employing an amphiphilic conjugated polymer PFPA-1 modified ITO coated glass substrate as the ohmic electron-collecting cathode and PEDOT:PSS PH1000 as the hole-collecting anode. For active layers based on different donor polymers, considerably lower reflection and parasitic absorption are found in the ST solar cells as compared to solar cells in the standard geometry with an ITO/PEDOT:PSS anode and a LiF/Al cathode. The ST solar cells have remarkably high internal quantum efficiency at short Circuit Condition (similar to 90%) and high transmittance (similar to 50%). Hence, efficient ST tandem solar cells with enhanced power conversion efficiency (PCE) compared to a single ST solar cell can be constructed by connecting the stacked two ST sub-cells in parallel. The total loss of photons by reflection, parasitic absorption and transmission in the ST tandem solar cell can be smaller than the loss in a standard solar cell based on the same active materials. We demonstrate this by stacking five separately prepared ST cells on top of each other, to obtain a higher photocurrent than in an optimized standard solar cell.
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.
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.