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    An advanced distributed power supply for power electronic transformers

    , Article IECON 2007, 33rd Annual Conference of the IEEE Industrial Electronics Society, Taipei, 5 November 2007 through 8 November 2007 ; 2007 , Pages 2038-2043 ; 1424407834 (ISBN); 9781424407835 (ISBN) Saghaleini, M ; Hekmati, A ; Farhangi, S ; Sharif University of Technology
    2007
    Abstract
    The idea of power electronic transformer (PET), which work with solid-state switches, have been considered noticeably recently. Every power electronic transformer has several parts which each of them needs its own reliable supply voltage. So the appropriate performance of a PET depends on the existence of various proper supply voltages. The distributed power supply (DPS), which can produce several different supply voltages simultaneously with various powers and high reliability, may be the optimum choice available for the supply of different modules of a PET. Additionally, distributed energy generation sources may be used as the alternative source for the PET which in that case it's... 

    HTS transformer windings design using distributive ratios for minimization of short circuit forces

    , Article Journal of Superconductivity and Novel Magnetism ; 2018 ; 15571939 (ISSN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer New York LLC  2018
    Abstract
    High-temperature superconducting (HTS) transformers have a promising feature in reduction of total weight, total size, and the losses of large-scale distribution transformers. However, the lower leakage reactance of HTS transformers results in a higher short-circuit fault currents and electromagnetic forces. Therefore, optimization of short-circuit electromagnetic forces is one of the crucial aspects in the design of HTS transformers. In this paper, a novel analytical method is proposed for determination of optimum distributive ratios resulting in minimization of these forces for asymmetrical multi-segment windings of an HTS transformer. Employing these distributive ratios, radial and axial... 

    Multi-segment winding application for axial short circuit force reduction under tap changer operation in HTS transformers

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 32, Issue 10 , 2019 , Pages 3171-3182 ; 15571939 (ISSN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer New York LLC  2019
    Abstract
    High-temperature superconducting (HTS) transformers have remarkable appealing advantages over conventional ones. But higher brittleness of HTS windings with respect to copper windings makes HTS transformers more vulnerable in short circuit and inrush current situations. During tap changer operation, appreciable asymmetry and non-uniform distribution of ampere-turn along the windings causes high axial component of short circuit forces and makes the situation more severe. In this paper, multi-segment winding method is employed for reduction of axial short circuit forces. An analytical method is presented for calculation of axial component of short circuit forces under tap changer operation.... 

    The impact of multilayered flux diverters on critical current in HTS transformer windings

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 481-485 ; 9781728115085 (ISBN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    Growing interest in high-temperature superconducting (HTS) power devices is the result of commercial availability of the HTS tapes. One of the most promising applications of the HTS technology is HTS transformer. Flux diverters are used for critical current elevation in HTS transformer windings. In this paper multilayered flux diverter arrangements have been introduced to reduce weight and losses of conventional solid flux diverter arrangement. Horizontal and vertical multilayered arrangements have been investigated and compared with solid arrangement. Two dimensional (2D) finite element method (FEM) simulations have been used for comparison between different arrangements  

    HTS transformer windings design using distributive ratios for minimization of short circuit forces

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 32, Issue 2 , 2019 , Pages 151-158 ; 15571939 (ISSN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer New York LLC  2019
    Abstract
    High-temperature superconducting (HTS) transformers have a promising feature in reduction of total weight, total size, and the losses of large-scale distribution transformers. However, the lower leakage reactance of HTS transformers results in a higher short-circuit fault currents and electromagnetic forces. Therefore, optimization of short-circuit electromagnetic forces is one of the crucial aspects in the design of HTS transformers. In this paper, a novel analytical method is proposed for determination of optimum distributive ratios resulting in minimization of these forces for asymmetrical multi-segment windings of an HTS transformer. Employing these distributive ratios, radial and axial... 

    HTS transformer’s partial discharges raised by floating particles and nitrogen bubbles

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 33, Issue 10 , 6 July , 2020 , Pages 3027-3034 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2020
    Abstract
    Presence of defects, conducting particles, nonconducting particles, and nitrogen gas bubbles in the insulation system of high-temperature superconducting (HTS) transformers, mainly inside the liquid nitrogen as its major insulation, can create local field enhancement and consequently partial discharges which eventually lead to the catastrophic failure of the transformer. In this paper, two-dimensional (2D) axisymmetric finite element method (FEM) modeling via COMSOL Multiphysics software has been utilized for the investigation of the impact of size and shape of conducting particles and nitrogen gas bubbles on partial discharge (PD) activities in liquid nitrogen. Conducting particles of... 

    HTS transformers leakage flux and short circuit force mitigation through optimal design of auxiliary windings

    , Article Cryogenics ; Volume 110 , September , 2020 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Mitigation and control of leakage fluxes and short circuit forces needs much more attention, for a high-temperature superconducting (HTS) transformer, than for a conventional one. Different methods such as the application of auxiliary windings, multi-segment winding, and flux diverter have been presented in the literatures for leakage magnetic field reduction in HTS transformers. In this paper, for the first time, optimal design of auxiliary windings has been performed for a 132/13.8 kV, 50 MVA three phase core type HTS transformer. Genetic algorithm (GA) has been used for the optimization process. Induced current in auxiliary windings which is inversely proportional to the leakage fluxes... 

    The end part of cryogenic H. V. bushing insulation design in a 230/20 kV HTS transformer

    , Article Cryogenics ; Volume 108 , June , 2020 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Appealing advantages of high-temperature superconducting (HTS) transformers are very promising for the contemporary and future power delivery systems. Cryogenic insulation technology is one of the key technologies for their commercialization. In this paper insulation design of the end part of cryogenic high voltage (H. V.) bushing of a 230/20 kV HTS transformer is developed. Analytical relations and finite element method (FEM) modelling, through application of COMSOL Multiphysics software, are employed for determination of electric field distribution in this design process. Weibull 0.1% dielectric breakdown strength has been considered as criterion for insulation design. Different shape and... 

    Optimal design of flux diverter using genetic algorithm for axial short circuit force reduction in HTS transformers

    , Article IEEE Transactions on Applied Superconductivity ; Volume 30, Issue 1 , January , 2020 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been... 

    Influence of electrostatic shielding of disc winding on increasing the series capacitance in transformer

    , Article 2007 IEEE Lausanne POWERTECH, Lausanne, 1 July 2007 through 5 July 2007 ; 2007 , Pages 1780-1784 ; 9781424421909 (ISBN) Bagheri, M ; Vakilian, M ; Hekmati, A ; Heidarzadeh, R ; Sharif University of Technology
    2007
    Abstract
    Strike of a lightning stroke to the high voltage terminal of a power transformer results in an impulse stress on its windings. The magnitude of the series capacitance of the windings has an important effect on the impulse voltage distribution and the stresses along the windings. Increasing the series capacitances of the windings, the impulse voltage distribution becomes more linear and the stress on the winding is reduced. So interleaved windings rather than disc windings are used in power transformer windings to increase the series capacitances. In this paper, the electrostatic shielding, used in disc windings to increase the windings series capacitance, and for linearization of its impulse... 

    Inductance calculation of HTS transformers with multi-segment windings considering insulation constraints

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 34, Issue 5 , 2021 , Pages 1329-1339 ; 15571939 (ISSN) Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2021
    Abstract
    High-temperature superconducting (HTS) transformers with multi-segment windings have been proposed in earlier literatures for the hysteresis loss reduction and short circuit electromagnetic force mitigation. The optimum distributive ratios for these multi-segment windings have been determined in earlier literatures. Asymmetrical seven segment winding with its optimum distributive ratio (k = 1/12) results in minimization of short circuit electromagnetic forces under normal tap and any adjusted tap. However, insulation design and leakage inductance calculation for the multi-segment winding of an HTS transformer have not been addressed in past literatures. Insulation design is one of the most... 

    Survey on high-temperature superconducting transformer windings design

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 33, Issue 9 , 8 June , 2020 , Pages 2581-2599 Moradnouri, A ; Ardeshiri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2020
    Abstract
    Utilization of superconducting equipment increases every day due to availability of the HTS tapes with reasonable prices, commercially. Since 1997, many high-temperature superconducting (HTS) transformers have been designed and fabricated. In this paper, all the different developments of HTS transformer windings since 1997 will be reviewed. Additionally, the advantages and disadvantages of the application of the two main winding types (the pancake and the layer) in the HTS transformer will be studied. © 2020, Springer Science+Business Media, LLC, part of Springer Nature  

    Impulse voltage distribution in intershield disk winding VS interleaved and continuous disk winding in power transformer

    , Article 2008 IEEE 2nd International Power and Energy Conference, PECon 2008, Johor Baharu, 1 December 2008 through 3 December 2008 ; 2008 , Pages 387-392 ; 9781424424054 (ISBN) Bagheri, M ; Hekmati, A ; Heidarzadeh, R ; Salay Naderi, M ; Sharif University of Technology
    2008
    Abstract
    Strike of a lightning stroke to the high voltage terminal of a power transformer results in an impulse stress on its windings. The magnitude of the series capacitance of the windings has an important effect on the impulse voltage distribution and the stresses along the windings. Increasing the series capacitances of the windings, the impulse voltage distribution becomes more linear and the stress on the winding is reduced. So interleaved windings rather than disk windings are used in power transformer windings to increase the series capacitances. In this paper, the electrostatic shielding, used in disk windings to increase the windings series capacitance, and for linearization of its impulse... 

    Application of advanced SVC incase of reactive power and unbalancy compensation of a locomotive

    , Article 2006 IEEE International Conference on Industrial Technology, ICIT, Mumbai, 15 December 2006 through 17 December 2006 ; 2006 , Pages 1897-1902 ; 1424407265 (ISBN); 9781424407262 (ISBN) Saghaleini, M ; Hekmati, A ; Rezaei, M. R ; Afsharnia, S ; Sharif University of Technology
    2006
    Abstract
    This paper introduces advanced SVC. Advanced SVC has been simulated with regard to reactive power and unbalancy compensation. Then, a new space has been chosen for state equation based on combination of d-q and real space to positive - negative. By decoupling of active, reactive powers and positive, negative sequences and using decoupling circuit, the facility of each sequence control, by control circuit will be provided independently. After advanced SVC modeling, the load - which is electrification railway system - will be simulated. So a sample of electric locomotive in Iran has been investigated and simulated. By using the load model, the advanced SVC has been used for compensation of...