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  • 1. Agheb, E.
    et al.
    Hashemi, E.
    Mousavi, Seyedali A.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Hoidalen, H. K.
    Study of very fast transient overvoltages in air-cored pulsed transformers2012In: Compel, ISSN 0332-1649, Vol. 31, no 2, p. 658-669Article in journal (Refereed)
    Abstract [en]

    Purpose - The purpose of this paper is to study very fast transient overvoltages (VFTOs) in the secondary winding of air-cored Tesla transformers and also study the resulting electric field stresses. Design/methodology/approach - An exhaustive model based on Multi-conductor Transmission Lines (MTLs) theory has been used. The governing telegraphist's equations have been solved by Finite Difference Time Domain (FDTD) method. Findings - The results demonstrated that there are some overvoltages at the end and middle turns that should be considered in insulation design. The magnitudes of these overvoltages are several times more than the steady state value of the corresponding turn which cause very high electric field stresses. Originality/value - The paper describes results obtained from an original and innovative implementation of FDTD method in transmission line modelling and is applied properly to air-cored pulse transformers.

  • 2.
    Carrander, Claes
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mousavi, Seyedali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES).
    An application of the time-step topological model for three-phase transformer no-load current calculation considering hysteresis2017In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 423, p. 241-244Article in journal (Refereed)
    Abstract [en]

    In many transformer applications, it is necessary to have a core magnetization model that takes into account both magnetic and electrical effects. This becomes particularly important in three-phase transformers, where the zero-sequence impedance is generally high, and therefore affects the magnetization very strongly. In this paper, we demonstrate a time-step topological simulation method that uses a lumped-element approach to accurately model both the electrical and magnetic circuits. The simulation method is independent of the used hysteresis model. In this paper, a hysteresis model based on the first-order reversal-curve has been used. © 2016 Elsevier B.V.

  • 3.
    Krings, Andreas
    et al.
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Mousavi, Seyedali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wallmark, Oskar
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Temperature Influence of NiFe Steel Laminations on the Characteristics of Small Slotless Permanent Magnet Machines2013In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 49, no 7, p. 4064-4067Article in journal (Refereed)
    Abstract [en]

    High performance electrical machines can operate at temperatures of 100 degrees C and beyond in rotor and stator cores. However, magnetic properties are generally measured at room temperatures around 23 degrees C to 25 degrees C according to the standards, even if it is known that the magnetization of some materials is substantially influenced by increasing temperatures. This paper investigates the thermal influence on the magnetic properties and iron losses in the stator cores of small slotless permanent magnet synchronous machines (PMSMs). The stator stack is made of thin nickel iron (NiFe) lamination sheets. Magnetic measurements of the stator core are conducted for different frequencies and flux densities at several temperatures between 25 degrees C and 105 degrees C. The obtained measurement data is afterwards used in finite element method (FEM) simulations to investigate the influence of the magnetic property change on the machine performance. For the PMSM in consideration, the FEM simulations show that an increased stator core temperature reduces the electromagnetic torque considerably; approximately 1/3 of the torque reduction due to increased rotor magnet and stator core temperatures (from 25 degrees C to 100 degrees C) can be attributed to the increased stator core temperature.

  • 4.
    Mousavi, Seyed Ali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electromagnetic Modelling of Power Transformers with DC Magnetization2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    DC currents that flow through the ground can be injected to the star windings of power transformers from their grounded neutral points and close their path with transmission lines. The geomagnetically induced currents (GICs) and AC/DC convertors of high voltage direct current (HVDC) systems are the sources of such DC currents. These currents may cause saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomenon results in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and misoperation of protective relays menaces the power network. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon

    Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC.

    Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis.

    In this project until now, a new algorithm for digital measurement of the core materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Three dimensional finite element models of various core types of power transformers are created to study the effect on them due to DC magnetization. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a distributed reluctance network method has been outlined. In this thesis a method for solving such a network problem with coupling to an electrical circuit and taking hysteresis into account is suggested.

  • 5.
    Mousavi, Seyed Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Implementation of hysteresis model in transient analysis of nonlinear reluctance networks2012In: ICEMS 2012 - Proceedings: 15th International Conference on Electrical Machines and Systems, 2012, p. 6401749-Conference paper (Refereed)
    Abstract [en]

    This paper introduces a method for implementation of hysteresis models in nonlinear reluctance networks for performing transient analyses. The proposed method for solving the nonlinear circuits is based on local linearization and doesn't have the problems of non-convergency and demands to high number of iteration. The ability of coupling between electrical and magnetic circuit make it very suitable for study transient phenomena in a power network related to nonlinearity of magnetic materials such as ferroresonance, inrush current and DC magnetization.

  • 6.
    Mousavi, Seyed Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Novel Method for Calculation of Losses in Foil Winding Transformers under Linear and non-Linear loads by Using Finite Element Method2010In: Advanced research workshop on transformers, ARWtr 2010, 2010, p. 326-331Conference paper (Other academic)
  • 7.
    Mousavi, Seyed Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Agheb, Edris
    Investigation of GIC effects on core losses in single phase power transformers2011In: Archives of Electrical Engineering, ISSN 0004-0746, Vol. 60, no 1, p. 35-47Article in journal (Refereed)
    Abstract [en]

    This paper presents a method for estimation of core losses in banks of single phase power transformers that are subjected to an injected DC current such as geomagnetically induced currents (GIC). The main procedure of the core loss calculation is to obtain a magnetic flux density waveform in both time and location by using a novel algorithm based on 3D FEM inside the core and then to calculate the loss distribution based on loss separation theory. Also, a simple and effective method is proposed for estimation of losses of asymmetric minor loops by using combination of symmetric loops. The effect of DC biasing on core losses in single phase power transformers is investigated and the sensitivity of core type and material is evaluated. the results shows that DC current biasing could increase core losses up to 40 percent or even more.

  • 8.
    Mousavi, Seyed Ali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Lotfi, A.
    Analytical hysteresis model for numerical electromagnetic simulations2015In: 2015 IEEE International Magnetics Conference, INTERMAG 2015, IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    Modelling of hysteresis in soft magnetic materials is necessary for accurate transient studies of transformers and electrical machines. The phenomena such as magnetization inrush currents and ferroresonance are directly resultants of the hysteresis properties. A proper model for numerical transient analyses should be easy regarding implementation and parameter estimation. In [1], authors introduced a differential hysteresis model derived from the Preisach classic theory. The model has accuracy comparable with Preisach models. Furthermore, in numerical simulations it can be inverted easily. In this paper, a practical method for estimation of the model functions by analytical expressions is suggested. The required input data is decreased to only the major hysteresis loop that is usually available that is easy to measure. Also, details of the numerical implementation are described. The presented method is verified by experimental measurements on several grain oriented and non-oriented electrical steels.

  • 9.
    Mousavi, Seyedali
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electromagnetic Modelling of Power Transformers for Study and Mitigation of Effects of GICs2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Geomagnetic disturbances that result from solar activities can affect technological systems such as power networks. They may cause DC currents in power networks and saturation of the core in power transformers that leads to destruction in the transformer performance. This phenomena result in unwanted influences on power transformers and the power system. Very asymmetric magnetization current, increasing losses and creation of hot spots in the core, in the windings, and the metallic structural parts are adverse effects that occur in transformers. Also, increasing demand of reactive power and malfunction of protective relays menaces the power network stability. Damages in large power transformers and blackouts in networks have occurred due to this phenomenon.

    Hence, studies regarding this subject have taken the attention of researchers during the last decades. However, a gap of a comprehensive analysis still remains. Thus, the main aim of this project is to reach to a deep understanding of the phenomena and to come up with a solution for a decrease of the undesired effects of GIC.

    Achieving this goal requires an improvement of the electromagnetic models of transformers which include a hysteresis model, numerical techniques, and transient analysis.

    In this project, a new algorithm for digital measurement of the magnetic materials is developed and implemented. It enhances the abilities of accurate measurements and an improved hysteresis model has been worked out. Also, a novel differential scalar hysteresis model is suggested that easily can be implemented in numerical methods. Two and three dimensional finite element models of various core types of power transformers are created to study the effect of DC magnetization on transformers. In order to enhance the numerical tools for analysis of low frequency transients related to power transformers and the network, a novel topological based time step transformer model has been outlined. The model can employ a detailed magnetic circuit and consider nonlinearity, hysteresis and eddy current effects of power transformers. Furthermore, the proposed model can be used in the design process of transformers and even extend other application such as analysis of electrical machines.

    The numerical and experimental studies in this project lead to understanding the mechanism that a geomantic disturbance affects power transformers and networks. The revealed results conclude with proposals for mitigation strategies against these phenomena.

  • 10.
    Mousavi, Seyedali A.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Differential Approach of Scalar Hysteresis Modeling Based on the Preisach Theory2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 10, p. 3040-3043Article in journal (Refereed)
    Abstract [en]

    This paper introduces a differential approach to model scalar hysteresis based on the Preisach theory. This model can generate hysteresis trajectories for both symmetrical and asymmetrical minor loops and keep the memory of a material in a proper manner. It can easily be inverted, it has a simple algorithm with suitable computational speed, and is not memory consuming. Also, the obtained results of the model are in very good agreement with measurements.

  • 11.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analysis of DC bias on leakage fluxes and electromagnetic forces in windings of power transformers based on three dimensional finite element models2013Conference paper (Refereed)
  • 12.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Investigation of Geomagnetcally Induced Current Effects on Core Losses in Single Phase Power Transformers2010Conference paper (Other academic)
  • 13.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Modelling static and dynamic hysteresis in time domain reluctance networks2014In: IET Conference Publications, 2014, no 627 CPConference paper (Refereed)
    Abstract [en]

    This paper introduces a novel method for taking into account the losses of magnetic materials in a time domain reluctance network analysis. The reluctance network method is a fast and practical method of electromagnetic analysis of magnetic devices. However, in conventional methods only non-linear properties of magnetic materials are considered. The method presented in this work improves the reluctance network method to manage both static hysteresis and dynamic eddy currents in the time domain. It can be used for calculation of losses and consider their effects in transient studies. The accuracy and efficiency of the method is confirmed by experiment.

  • 14.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Three dimensional finite element analyses of transformer core joints with respect to the magnetization current2011Conference paper (Other academic)
  • 15.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Carrander, Claes
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Comprehensive Study on Magnetization Current Harmonics of Power Transformers due to GICs2013Conference paper (Refereed)
    Abstract [en]

    This paper studies the effect of DC magnetization of power transformers on injected harmonics to power systems. DC magnetization due to geomagnetically induced currents can saturate the core of a power transformer during a half cycle. It causes a very asymmetric, high value magnetization current that contains large harmonic components.

    In this work, by using a three-dimensional finite element model, the effect of core type and DC current level on generated harmonics is investigated.

    The results could help power system engineers to choose the proper types of power transformers and improve the protection aspects of the network.

     

  • 16.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Carrander, Claes
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Electromagnetic transients due to interaction between power transformers and network during a GIC attack2013Conference paper (Refereed)
  • 17.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Implementation of novel topology based transformer model for analyses of low frequency transients2013Conference paper (Refereed)
  • 18.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Novel Algorithm for measurements of static properties of magnetic materials with digital system2013Conference paper (Refereed)
  • 19.
    Mousavi, Seyedali
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Engdahl, Göran
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Krings, Andreas
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Bissal, Ara
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Novel Method for Measurement of Anhysteretic Magnetization Curves2013Conference paper (Refereed)
1 - 19 of 19
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