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  • 1.
    Abrahamsson, Curt Johan David
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fregelius, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bladh, Johan
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic thrust bearing for a 10 MW hydropower generator with a Kaplan turbine2018Conference paper (Refereed)
  • 2. Aidanpää, J.-O
    et al.
    Gustavsson, R. K.
    Lundström, N. L. P
    Karlsson, M.
    Calleecharan, Y.
    Nässelqvist, M. L.
    Karlberg, M.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Developments in Rotor Dynamical Modeling of Hydropower units2009Conference paper (Refereed)
  • 3. Bladh, Johan
    et al.
    Sundqvist, Per
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Torsional stability of hydropower units under influence of subsynchronous oscillations2013In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, no 4, p. 3826-3833Article in journal (Refereed)
    Abstract [en]

    Hydropower units are known to be comparatively insensitive to subsynchronous power oscillations. During a startup test of an electrical island in the Nordic power system, a series capacitor tripped due to a subsynchronous oscillation within the normal frequency range of hydropower unit torsional modes. Since no thermal units were connected, it is motivated to question the traditional view. In this paper, the small-signal and transient torsional mode stability of hydropower units is assessed through time-domain simulations. The model is based on the first IEEE benchmark model for subsynchronous resonance which has been tuned to fit one of the blackstart test system units for which detailed measurements are available. The stability conditions are investigated for several load conditions and machine configurations. It is found that the damping in the startup test system is sufficient to prevent growing oscillations. A fault however could expose the machines to high transient torques.

  • 4.
    Bladh, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wallin, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saarinen, Linn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements2016In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 46-56Article in journal (Refereed)
    Abstract [en]

    Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.

  • 5.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Poynting theorem applied to cable wound generators2008In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, no 2, p. 600-605Article in journal (Refereed)
    Abstract [en]

    The use of cable windings in generators and transformers has a physical background which is hard to neglect. The work done by Maxwell, Poynting and Slepian combined with powerful finite element solver of today allows for visualization of electric and magnetic fields in different geometries. The electromagnetic fields and power flows for generator stator cables are in this article associated with Poynting's theorem. Geometrical design and insulation material properties are then linked to Poynting's theory showing that circular stator cables enable higher voltages while maintaining a high power flow. Today several high voltage generators and two transformers have been built and are currently in operation. This paper discusses the application of the Poynting Theorem to cable wound generators.

  • 6.
    Dahlborg, Elin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Vattenfall AB.
    Saarinen, Linn
    Vattenfall Hydropower AB.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Improving frequency control from Kaplan turbines to fulfill grid codes2019In: HYDRO 2019, Porto, Portugal, 14-16 October, 2019., Aqua Media International Ltd , 2019Conference paper (Refereed)
  • 7.
    de Santiago Ochoa, Juan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaína
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Larsson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Losses in Axial-Flux Permanent-Magnet Coreless Flywheel Energy Storage Systems2008Conference paper (Refereed)
  • 8.
    Felicetti, Roberto
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, C. Johan D.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Experimentally validated model of a fast switched salient pole rotor winding2019In: 2019 IEEE Workshop on Electrical Machines Design, Control and Diagnosis (WEMDCD), IEEE, 2019, p. 150-156Conference paper (Refereed)
    Abstract [en]

    The article proposes a model of a salient pole synchronous machine field winding based on a single transmission line model. An experimental method to derive the parameters is also presented and validated. Finally, the measured voltage distribution in the winding is compared to the model voltage distribution and the results match, demonstrating the model capabilities. The model describes the intrinsic resonance phenomena and accurately determines the voltage amplification factor.

  • 9.
    Kougias, Ioannis
    et al.
    European Commiss, JRC, Ispra, Italy.
    Aggidis, George
    Univ Lancaster, Dept Engn, Lancaster, England.
    Avellan, Francois
    Ecole Polytech Fed Lausanne, Hydraul Machines Lab, Lausanne, Switzerland.
    Deniz, Sabri
    Hsch Luzern, Lucerne Sch Engn & Architecture, Luzern, Switzerland.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Moro, Alberto
    European Commiss, JRC, Ispra, Italy.
    Muntean, Sebastian
    Romanian Acad, Ctr Adv Res Engn Sci, Bucharest, Romania.
    Novara, Daniele
    Trinity Coll Dublin, Dept Civil Struct & Envir Engn, Dublin, Ireland.
    Ignacio Perez-Diaz, Juan
    Tech Univ Madrid, Dept Hydr Energy & Envir Engn, Madrid, Spain.
    Quaranta, Emanuele
    Politecn Torino, Dept Environ Land & Infrastruct Engn, Turin, Italy.
    Schild, Philippe
    European Commiss, DG Res & Innovat, Dir Energy, Brussels, Belgium.
    Theodossiou, Nicolaos
    Aristotle Univ Thessaloniki, Dept Civil Engn, Thessaloniki, Greece.
    Analysis of emerging technologies in the hydropower sector2019In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 113, article id 109257Article, review/survey (Refereed)
    Abstract [en]

    The paper reviews recent research and development activities in the field of hydropower technology. It covers emerging and advanced technologies to mitigate flow instabilities (active and passive approach) as well as emerging magneto-rheological control techniques. Recent research findings on flow instabilities are also presented, especially concerning fluid-structure interaction and transient operating conditions. As a great number of the existing large-scale hydroelectric facilities were constructed decades ago using technologies that are now considered obsolete, technologies to achieve the digitalisation of hydropower are also analysed. Advances in the electro-mechanical components and generator design are presented; their potential role to adapt hydropower to the current operating conditions is also highlighted. The text explores current efforts to advance hydropower operation, mainly in terms of European projects. It provides a detailed overview of the recent efforts to increase the operational range of hydraulic turbines in order to reach exceptional levels of flexibility, a topic of several recent research projects. Variable speed hydropower generation and its application in pumped storage power plants are presented in detail. Moreover, revolutionary concepts for hydroelectric energy storage are also presented with the analysis focusing on underwater hydro storage and hydropower's hybridisation with fast energy storage systems. Efforts to minimise hydropower's environmental footprint are also presented via the utilisation of small-scale and fish-friendly installations.

  • 10.
    Kristiansen Nøland, Jonas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol Nat Sci & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Comparison of Thyristor Rectifier Configurations for a Six-Phase Rotating Brushless Outer Pole PM Exciter2018In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 2, p. 968-976Article in journal (Refereed)
    Abstract [en]

    Recent technological developments have caused a renewed interest in the brushless excitation system. With the application of wireless communication, the conventional diode bridge has been replaced with fully controllable thyristors on the shaft. It offers the same dynamic performance as the conventional static excitation system. The thyristor bridge of the conventional three-phase exciter needs to be controlled with a high firing angle in normal operation in order to fulfill a requirement of both a high ceiling voltage and a high ceiling current. A high firing angle causes high torque ripple to be absorbed by the exciter stator and a low power factor results in a low utilization of the designed exciter. In this contribution, we present a strategy that solves this problem by looking into combinations of thyristor configurations of a double-star six-phase connection of the exciter. Experimental results are used to verify the circuit models implemented for this investigation. A hybrid-mode 12-pulse thyristor bridge configuration seems to be a good solution for implementations in commercial apparatus. An additional switch interconnects two separate thyristor bridges from parallel- to series connection at the rectifier output, and utilizes the advantages of both topologies.

  • 11.
    Leijon, Mats
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Bolund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Avdelningen för elektricitetslära och åskforskning.
    High Voltage Generators; Ideas behind them and Operation Data2006Conference paper (Other academic)
  • 12. Lidenholm, Johan
    et al.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests2010In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, p. 931-939Article in journal (Refereed)
    Abstract [en]

    Four standard test procedures-the three phase short-circuit test, the field decrement test, the slip test, and the applied voltage test-for estimation of synchronous generator parameters have been implemented in a time-stepping finite-element software. In this paper, the main features of the implementation and the post-processing of data are described. The validity of the application is demonstrated by comparison with test results from the commissioning of a large hydropower generator. The method is shown to be effective in estimating most parameters. Better representation of the exciter and the interpole connections of the damper circuit is believed to enhance the compliance even further.

  • 13.
    Lidenholm, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ranlöf, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Comparison of field and circuit generator models in single machine infinite bus system simulations2010In: Electrical Machines (ICEM), 2010 XIX International Conference on, 2010Conference paper (Refereed)
    Abstract [en]

    This paper compares the transient response of a finite element salient pole synchronous generator model connected to an infinite network bus to that of a system model based on an equivalent circuit representation of the machine. The characteristics and operating conditions of the two models are made equal as far as possible by thoroughgoing initiation and by using the finite element model for estimation of the circuit model parameters. It is found that the circuit model underestimates the stiffness and damping properties of the machine in comparison with the electromagnetic model, which largely is believed to be attributable to inadequate representation of the rotor circuits. The results raise questions regarding some common applications of equivalent circuit models.

  • 14.
    Lidenholm, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ranlöf, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effects of including automatic excitation control in transient field simulations of hydrogenerators2009In: Proceedings of the 44th International Universities Power Engineering Conference, University of Strathclyde Glasgow, 2009Conference paper (Refereed)
    Abstract [en]

    This paper addresses effects of automatic excitation control in time-stepped finite element analysis of hydroelectric generators. A simple method to incorporate exciter and automatic voltage regulator models in a finite element software is presented and tested on a small hydropower generator connected to a three-phase power system equivalent. Three simulations are performed to demonstrate the impact of the controller and to compare the field voltage and the field current as two possible excitation source variables. It is shown that inclusion of the excitation system greatly enhances the damping of rotor-angle oscillations and that the field voltage should be chosen as source variable to include the transient field winding inductance in the field problem.

  • 15. Lidström, Erica
    et al.
    Wall, Daniel
    Persson, Jonas
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Voltage stability at hydropower stations influenced by close-located wind farms2012Conference paper (Refereed)
  • 16.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bolund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Poynting Vector Analysis of Synchronous Generators Using Field Simulations2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 9, p. 3601-3606Article in journal (Refereed)
    Abstract [en]

    The Poynting vector has been used to gain an understanding of energy flow in rotating electrical machines. Previous studies of energy flow in rotating electrical machines have used the Poynting vector in crude formulas to obtain a qualitative picture. In this paper, we present a study based on numerically calculated fields and quantities entering the Poynting vector. We obtained a detailed understanding of how energy flows in the air gap and into the winding of a synchronous generator. In particular, we found that, at no-load, energy is flowing both to and from the stator as a result of cogging, while for normal load cases the energy flow is unidirectional.

  • 17.
    Lundin, Urban
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Theoretical Magnetism.
    Sandalov, Igor
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Theoretical Magnetism.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Theoretical Magnetism.
    Theory of strongly correlated electron systems. II. Including correlation effects into electronic structure calculations2005In: Theory of strongly correlated electron systems. II. Including correlation effects into electronic structure calculations, ISSN 0020-7608, Vol. 102, no 6, p. 1046-Article in journal (Refereed)
    Abstract [en]

    We have previously shown that a division of the f-shell into two subsystems gives a better understanding of the cohesive properties as well the general behavior of lanthanide systems. In this article, we present numerical computations, using the suggested method. We show that the picture is consistent with most experimental data, e.g., the equilibrium volume and electronic structure in general. Compared with standard energy band calculations and calculations based on the self-interaction correction and LIDA + U, the f-(non-f)-mixing interaction is decreased by spectral weights of the many-body states of the f-ion.

  • 18.
    Lundin, Urban
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wolfbrandt, Arne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Method for modeling time-dependent nonuniform rotor/stator configurations in electrical machines2009In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 7, p. 2976-2980Article in journal (Refereed)
    Abstract [en]

    Nonuniform air gaps in electrical machines cause problems with forces and noise. There are a number of analytical and numerical methods to calculate the response due to nonuniform air gaps. In this paper, we present an efficient method based on an effective air gap permeability. Our unified method enables all nonuniform rotor-stator configurations to be simulated. We provide some results from simulations of static and dynamic eccentricity as well as irregularity.

  • 19.
    Marcusson, Birger
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Axial Magnetic Fields at the Ends of a Synchronous Generator at Different Points of Operation2015In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 2, article id 8100208Article in journal (Refereed)
    Abstract [en]

    Axial magnetic fields leaking out at the ends of a conventional rotating synchronous machine cause losses. Therefore, it is important to be able to predict the axial magnetic fields. A linear steady-state model for the axial magnetic flux density phasor in the end regions of non-salient synchronous generators has previously been verified experimentally. This paper describes an extension of the model to salient pole synchronous generators and a method for calculating the coefficients. Experiments and 3-D finite element simulations justify a distinction between axial flux density contributions from the d and q components of the stator current. How the coefficients and the axial magnetic fields in the ends of a small synchronous generator change with steady-state operation conditions is here shown with measurements and to some extent with 3-D finite element simulations.

  • 20.
    Marcusson, Birger
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Axial Magnetic Fields, Axial Force, and Losses in the Stator Core and Clamping Structure of a Synchronous Generator with Axially Displaced Stator2017In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 45, no 4, p. 410-419Article in journal (Refereed)
    Abstract [en]

    Axial displacement of the stator in a synchronous machine gives rise to axial magnetic field both at the ends and deep inside the stator. The axial magnetic field causes losses. This article contains results from two studies with an axially displaced stator. In the first study, axial magnetic leakage fields in the ends of a small synchronous generator at load and no load were measured and simulated. In the second study, axial force and iron losses at no load were calculated with non-linear materials and a three-dimensional, time-stepped finite element method. For some machines with vertical shafts, the sum of iron losses and thrust bearing losses can be reduced if the rotor is lowered or the stator raised, whichever is best.

  • 21.
    Marcusson, Birger
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Harmonically Time Varying, Traveling Electromagnetic Fields along a Plate and a Laminate with a Rectangular Cross Section, Isotropic Materials and Infinite Length2017In: Progress in Electromagnetics Research B, ISSN 1937-6472, E-ISSN 1937-6472, Vol. 77, p. 117-136Article in journal (Refereed)
    Abstract [en]

    This article contains derivation of propagation factors and Fourier series for harmonically time varying, traveling electromagnetic fields in a plate and a laminate with rectangular cross sections, isotropic materials and infinite length. Different and quite general fields are taken into account on all boundaries. Choices of boundary conditions and continuity conditions are discussed. Certain combinations of types of boundary conditions make the derivation possible for a laminate. Comparisons are made between results of Fourier series and finite element calculations.

  • 22.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Active Current Sharing Control Method for Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters2018In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 2, p. 893-896Article in journal (Refereed)
    Abstract [en]

    A new high-speed-response dual-star brushless rotating exciter has been recently proposed, which utilizes two rotating thyristor rectifiers in a hybrid-mode topology. However, dissymmetries tend to occur in large-scale apparatus, which ultimately results in an undesired unbalanced loading of the topology. Moreover, the topology provides a possibility for compensation via asymmetrical firing, which serves as a promising solution to be investigated. This letter proposes an active current sharing adjustment method between the parallel thyristor bridges. The method improves controllability and performance compared with the alternative “skip firing” approach, and it can replace the interphase reactors (IPRs) in large direct current applications.

  • 23.
    Nøland, Jonas Kristiansen
    et al.
    Department of Microsystems, University of South-Eastern Norway, Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Department of Microsystems, University of South-Eastern Norway, Borre, Norway.
    Failure Modes Demonstration and Redundant Postfault Operation of Rotating Thyristor Rectifiers on Brushless Dual-Star Exciters2019In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 2, p. 842-851Article in journal (Refereed)
    Abstract [en]

    The excitation system plays a critical role in the operation of synchronous generators. An equipment failure could impact the voltage quality for smaller grids. Further, it can lead to cost penalties and reduced production for the power plant owner. Recently, a new high-speed-response rotating brushless exciter was developed that employs remote control of the rotating thyristors on the generator shaft. This has led to new possibilities for improving the performance of brushless exciters. This contribution investigates the failure modes of a dual-star outer pole exciter that feeds two separate thyristor bridges connected in parallel during normal operation. The possibility of redundant postfault operation due to open-thyristor or open-phase faults are demonstrated using experimental testing. The system is compared with the fault performance of a conventional three-phase system. This work includes the implementation and validation of a fault-predicting double d-q exciter model. In addition, the dangerous effects of a shorted-thyristor fault are investigated. A "skip firing" protection technique is briefly demonstrated for the fast isolation of such faults, yielding nondestructive postfault recovery and redundant failure-mode operation. The evidence shows that the dual-star exciter is a competitive choice for the future development of fault-tolerant brushless exciters.

  • 24.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, J. José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design and Characterization of a Rotating Brushless Outer Pole PM Exciter for a Synchronous Generator2017In: IEEE transactions on industry applications, ISSN 0093-9994, E-ISSN 1939-9367, Vol. 53, no 3, p. 2016-2027Article in journal (Refereed)
    Abstract [en]

    Generally, PM machines are used as PMG pre-exciters in 3-stage brushless excitations systems. This paperpresents the design, characterization and prototyping of a rotatingbrushless PM exciter used in a proposed 2-stage excitation systemfor a synchronous generator. The proposed design reduces thenumber of components compared with conventional systems.A comparison with the state-of-the-art conventional excitationsystems is given. The design of a fast-response, or high initialresponse, brushless exciter requires active rectification on therotating frame, replacing the non-controllable diode bridge. Theobjective was to construct an exciter with the capability of a50 Aoutput field current as well as a high value of the available ceilingvoltage and ceiling current. The final exciter was constructed to befitted into an in-house synchronous generator test setup. A finiteelement model of the exciter was validated with experimentalmeasurements. The exciter prototype is also compared with analternative armature design with non-overlapping single-layerconcentrated windings but with the same main dimensions.The paper includes a general design procedure suitable foroptimization of PM brushless exciters that fulfill the requirementsof their synchronous generators and the grid.

  • 25.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesus José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup2016In: Design and characterization of a rotating brushless PM exciter for a synchronous generator test setup / [ed] IEEE Xplore, 2016, p. 259-265Conference paper (Refereed)
    Abstract [en]

    This paper deals with the characterization and construction of a rotating brushless PM exciter intended for synchronous generator excitation purposes. Traditionally, PM exciters are used as pre-exciters in synchronous generator excitations systems. In order to reduce the number of components and to increase the step time response of the system, a PM exciter is designed as an outer pole PM machine, with permanent magnets on the stator and armature windings on the rotor. The exciter was constructed electrically and mechanically to be fitted into an in-house synchronous generator test setup. A finite element model of the exciter was validated with no-load measurements of voltages and magnetic flux densities. The exciter was then characterized with unsaturated and saturated parameters.

  • 26.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Dept Engn, Fac Technol & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evaluation of different power electronic interfaces for control of a rotating brushless PM exciter2016In: Proceedings Of The IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society, IEEE, 2016, p. 1924-1929Conference paper (Refereed)
    Abstract [en]

    his paper investigates the performance of different power electronic interfaces for a rotating brushless permanent magnet exciter, designed for a synchronous generator test setup. A passive rotating diode bridge is commonly used as the rotating interface on conventional brushless excitation systems. Those systems are known to be slow dynamically, since they cannot control the generator field voltage directly. Including active switching components on the rotating shaft, like thyristors or transistors, brushless excitation systems can be comparable to static excitation systems. Brushless excitation systems has the benefit of less regular maintenance. With permanent magnets on the stator of the designed exciter, the excitation system improves its field forcing capability. Results show that modern power electronic interfaces utilize the exciter machine optimally, increase the power factor, reduce the torque pulsations, maintain the available field winding ceiling voltage and improve the field winding controllability.

  • 27.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Univ Coll Southeast Norway, Fac Technol Nat Sci & Maritime Sci, N-3184 Borre, Norway.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Testing of Active Rectification Topologies on a Six-Phase Rotating Brushless Outer Pole PM Exciter2018In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 33, no 1, p. 59-67Article in journal (Refereed)
    Abstract [en]

    The static exciter is dominating among large grid-connected generators due to the weak dynamic performance of conventional brushless exciters. In this paper, a six-phase outer pole permanent magnet rotating brushless exciter is evaluated with different active rectification topologies. Both thyristor-based and chopper-based topologies are considered. A fast-response brushless excitation system is obtained by replacing the conventional rotating diode bridge rectifier with the proposed active rectification topologies on the shaft. The given two-stage system generates its own excitation power directly from the shaft, contrary to static exciters. The selection of an appropriate rectification topology could minimize the rotor armature phase currents for a given generator field current. The objective is a high power factor and a high utilization of the exciter machine. An optimal rectification topology makes higher ceiling currents possible, improving the transient behavior of the synchronous generator. In this paper we show that six-phase topologies add complexity, but improve exciter redundancy, increase the available ceiling voltage and reduce the steady state torque ripple. Experimental results are given for validating the models implemented for the analysis.

  • 28.
    Nøland, Jonas Kristiansen
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hjelmervik, Karina Bakkeløkken
    Buskerud and Vestfold University College.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Comparison of Thyristor-Controlled Rectification Topologies for a Six-Phase Rotating Brushless Permanent Magnet Exciter2016In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, no 1, p. 314-322Article in journal (Refereed)
    Abstract [en]

    The thyristor bridge rectifier has proven to be a reliable solution regarding control of excitation equipment for synchronous generators. However, in rotating brushless exciters, the diode rectifier is the dominant topology on the shaft. In order to improve the step response of rotating exciters, one could put a thyristor bridge rectifier on the rotating part and control the firing angle remotely from a stationary controller. This paper compares different multiphase configurations of permanent magnet synchronous machines as a rotating exciter and discusses the possibility to reduce the torque ripple by selecting the appropriate rectification topology. The paper also explains the implications of the self and mutual inductances of the armature windings for the performance of the exciter.

  • 29.
    Nøland, Jonas Kristiansen
    et al.
    Univ Coll Southeast Norway, Dept Engn, Fac Technol & Maritime Sci, Bone, Norway.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Step time response evaluation of different synchronous generator excitation systems2016In: Step time response evaluation of different synchronous generator excitation systems, IEEE Xplore, 2016Conference paper (Refereed)
    Abstract [en]

    A fast step response of an excitation system is critical for a synchronous generator in order to maintain stability under disturbances in the interconnected power grid. This is the main reason that the static excitation system has been preferred for large synchronous generators. Some transmission system operators even have requirements that the excitation system should be static for synchronous generators above a certain size. The requirement is set in order to fulfill a certain goal for the step time response. As technology progresses forward, the static excitation system will not any longer be the only option for a fast controllable excitation system. New brushless rotating excitation systems, with wireless control interfaces, can be even faster than the static excitation system. They also reduce the need of maintenance of the synchronous generator. With permanent magnet exciters, the excitation system can be independent from the grid, maintaining the excitation response under voltage dips in the power grid. This paper evaluates the dynamic performance of the static excitation system compared with different types of brushless rotating excitation systems.

  • 30.
    Perers, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Development of synchronous generators for Swedish hydropower: A review2007In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 11, no 5, p. 1008-1017Article, review/survey (Refereed)
    Abstract [en]

    The development of large-scale hydropower in Sweden started around 1900 when the Swedish government considered replacing of steam engine power with power from water falls, especially for utilization in railway operation. The hydropower development extends more than hundred years. Most of the Swedish hydropower was built in 1950s and 1960s. Due to the advancing age of installations, Sweden is facing an extensive refurbishment work in the upcoming decades. A large variety of individual designs exist among hydroelectric generators. The generator design has constantly strived for more compact and cost-effective constructions and this has resulted in a constant increase in the unit size. This paper describes the evolution of hydropower generators in Sweden. The development of assembling, stator insulation, cooling and materials used are described.

  • 31.
    Perers, Richard
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saturation Effects on Unbalanced Magnetic Pull in a Hydroelectric Generator With an Eccentric Rotor2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 10, p. 3884-3890Article in journal (Refereed)
    Abstract [en]

    We report an investigation of saturation effects on the unbalanced magnetic pull in a hydroelectric generator with 20% static eccen-tricity. We determine the magnetic pull force by the finite-element method in parallel with a simple analytical model for various no-loadvoltages and loads. Saturation significantly affects the magnitude of the unbalanced magnetic pull for high voltages and large loads.

  • 32.
    Perez-Loya, J. Jose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Initial Performance Tests of a Permanent Magnet Thrust Bearing for a Hydropower Synchronous Generator Test-Rig2016Conference paper (Refereed)
  • 33.
    Perez-Loya, J. Jose
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Optimization of Force Between Cylindrical Permanent Magnets2014In: IEEE Magnetics Letters, ISSN 1949-307X, E-ISSN 1949-3088, Vol. 5, p. 0800404-Article in journal (Refereed)
    Abstract [en]

    We calculated analytically and with the finite-element method the force between two identical coaxial cylindrical magnets for nine different magnetic materials at separations of 1, 3, 5, 7, and 9 mm and for height-to-diameter ratios between 0.1 and 2. For the analytical calculations, we assumed homogeneous magnetization. For the nonhomogeneous case, we used the finite-element method taking into consideration the magnetic flux density vs. field (B-H) curves of the materials. The results show that, similarly for cuboid magnets, the maximum force for a given volume of permanent-magnet material was achieved for a height-to-diameter ratio around 0.4 for homogeneously magnetized (ideal) permanent magnets. We also show that this is not always true for the nonhomogeneous cases. The resulting forces are dependent on the B-H curve of the magnets. As the B-H curves of the materials deviate from their ideal counterparts, the aspect ratio that yields maximum force increases.

  • 34.
    Perez-Loya, Juan José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Demonstration of Synchronous Motor Start by Rotor Polarity Inversion2018In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 65, no 10, p. 8271-8273Article in journal (Refereed)
    Abstract [en]

    Synchronous motors are reliable and efficient, but it is relatively difficult to start them. In some cases, a variable frequency drive is utilized. In some other, asynchronous start is achieved by virtue of induced currents in a solid rotor, or a rotor damper cage installed for this purpose. In this contribution, a method to start a synchronous machine without a damper cage is presented. The starting was achieved by inverting the polarity of the rotor field winding in a timely manner with respect to the rotating stator field. The technique was verified with experiments performed on a 200 kVA experimental test rig and also simulated on a 20 MVA machine.

  • 35.
    Pérez-Loya, J. José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simple Method to Calculate the Force between Thin Walled Solenoids2016In: Progress In Electromagnetics Research M, ISSN 1937-8726, Vol. 51, p. 93-100Article in journal (Refereed)
    Abstract [en]

    We developed a simple method to calculate the axial force between concentric thin walled solenoids. To achieve this, the force between them was mapped as a function of their geometrical relations based on separation-to-diameter ratios. This resulted in an equation and a set of data. We used them together to calculate axial forces between two coaxial thin walled solenoids. With this method, direct evaluation of elliptical integrals was circumvented, and the forces were obtained with a simple expression. The results were validated against solutions obtained with an existing semi-analytical method and force measurements between high coercivity permanent magnets.

  • 36.
    Pérez-Loya, Jesus José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    de Santiago, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Construction of a Permanent Magnet Thrust Bearing for a Hydropower Generator Test Setup2013Conference paper (Refereed)
  • 37.
    Pérez-Loya, Jesus José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rodriguez, E.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stephan, R. M.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic Modeling and Measurement of Forces Between Permanent Magnet Rings used as Passive Magnetic Bearings2013Conference paper (Refereed)
  • 38.
    Pérez-Loya, Jesús José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evestedt, Fredrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance tests of a permanent magnet thrust bearing for a hydropower synchronous generator test-rig2017In: ACES Journal, Vol. 32, no 8, p. 704-711Article in journal (Refereed)
    Abstract [en]

    Permanent magnets are an attractive material to be utilized in thrust bearings as they offer relatively low losses. If utilized properly, they have a long service lifetime and are virtually maintenance free. In this contribution, we communicate the results of the tests performed on a permanent magnet thrust bearing that was custom built and installed in a hydropower synchronous generator test-rig. Tridimensional finite element simulations were performed and compared with measurements of axial force. Spin down times and axial force ripple have also been measured. We found good correspondence between the measurements and the simulations.

  • 39.
    Pérez-Loya, Jesús José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electromagnetic losses in synchronous machines during active compensation of unbalanced magnetic pull2018In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 66, no 1, p. 124-131Article in journal (Refereed)
    Abstract [en]

    Unbalanced magnetic pull (UMP) is typically caused by rotor or stator shape defects, electrical short circuits, eccentric rotor/stator bores, as well as unreasonable pole-slot combinations. It leads to vibration and increases noise and energy losses of the machine. By actively controlling the magnetic fields and forces that arise between the rotor and stator by regulating the rotor field current of separated pole groups, it is possible to cancel it. In this paper, we measure and calculate the currents induced in the damper bars for a synchronous machine test rig under 20% static eccentricity with and without active compensation of UMP. This is done to validate our finite-element calculations. Afterward, we perform loss calculations for a 74-MVA synchronous generator with and without stator parallel circuits. We find that, with active compensation of UMP for an eccentric machine, the damper bar currents and stator parallel circuit circulating currents can be eliminated and the electromagnetic efficiency of the machine that has a static eccentricity fault increases.

  • 40.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bladh, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators2013In: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 44, no 1, p. 844-851Article in journal (Refereed)
    Abstract [en]

    Damping and synchronizing torque coefficients are calculated from time-stepped finite element simulations of a hydroelectric generator connected to an infinite busbar. The calculated torque coefficients are compared to those obtained from two-axis equivalent circuit simulations as well as classical analytical expressions. The influence of the damper winding type, and the size and nature of the system disturbance on the damping and synchronizing torques is explored. It is found that a finite element model of a hydroelectric generator typically exhibits both higher damping and synchronizing properties compared to a two-axis circuit equivalent of the same unit. In particular, the damping and synchronizing contributions from a continuous damper winding are substantially higher in the finite element model than in the equivalent circuit model. Moreover, explicit consideration of dynamic iron losses is found to not affect the damping and synchronizing torques predicted by the finite element model.

  • 41.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Connor, Gary
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Simulation of a Radial Flux Permanent Magnet Generator with Two Contra-Rotating Rotors2008Conference paper (Refereed)
  • 42.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Finite Element Analysis of a Permanent Magnet Machine with Two Contra-rotating Rotors2009In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 37, no 12, p. 1334-1347Article in journal (Refereed)
    Abstract [en]

    Electrical machines with contra-rotating rotors find applications in direct-drive energy conversion systems and in ship propulsion systems that employ hydraulic machinery with two contra-rotating stages. In this article, the operating characteristics of permanent magnet machines with two contra-rotating rotors moving on opposite sides of a common stator core are studied via two-dimensional finite element analysis. Particular attention is devoted to the special flux distortion patterns that arise in contra-rotating machine topologies. The study suggests that the introduction of a screening iron core between the rotors provides for negligible flux distortion levels during contra-rotating synchronous operation of the two rotors.

  • 43.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Form Factors and Harmonic Imprint of Salient Pole Shoes in Large Synchronous Machines2011In: Electric power components and systems, ISSN 1532-5008, E-ISSN 1532-5016, Vol. 39, no 9, p. 900-916Article in journal (Refereed)
    Abstract [en]

    This article presents a review of the connection between salient pole shoe shapes and form factors that model saliency affects in synchronous machine design programs. Additionally, the impact of the pole shape on the harmonic contents of the air-gap flux density waveform is examined. The properties of different pole shoes are assessed with 2-D finite element analysis in the working environment of a large hydro-electric generator topology. The influence of magnetic saturation is particularly emphasized. Linear models for the calculation of form factors are established. It is concluded that the choice of pole shoe design typically must be a compromise between a high field and direct axis form factor and a low total harmonic distortion.

  • 44.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    The Rotating Field Method Applied to Damper Loss Calculation in Large Hydrogenerators2010Conference paper (Refereed)
    Abstract [en]

    In this paper, we discuss key aspects of analytical rotating field models that can be used to estimate the damper losses in large hydrogenerators during steady load conditions. Model features of particular importance, like the saturation permeance and the structure of the damper circuit are described in greater detail. Damper currents extracted from the analytic model are found to be in good agreement with currents obtained from coupled field-circuit 2-D finite element calculations. The applicability of the model for damper current prediction during steady unbalanced load conditions is also demonstrated.

  • 45.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Perers, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On Permeance Modeling of Large Hydrogenerators With Application to Voltage Harmonics Prediction2010In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, no 4, p. 1179-1186Article in journal (Refereed)
    Abstract [en]

    In this paper, a permeance model that can be employed to estimate the no-load damper current loss and voltage waveform harmonics in large hydrogenerators is presented. The importance of modeling the damper magnetomotive force and inductances correctly is emphasized, and detailed descriptions are presented. The computed harmonics are compared with values obtained from time-stepped finite-element calculations and measured data. The results are in good agreement. The influence of pole-to-pole damper bar connections, and of the number of damper bars on the voltage waveform, is explained.

  • 46.
    Ranlöf, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wolfbrandt, Anna
    Lidenholm, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Core Loss Prediction in Large Hydropower Generators: Influence of Rotational Fields2009In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 45, no 8, p. 3200-3206Article in journal (Refereed)
    Abstract [en]

    In this paper, we discuss the accuracy of several core loss models as compared to experimental data obtained from measurements on commercial hydropower generators. Our aim in this paper is twofold. First, we emphasize the problem of total core loss prediction by comparing the core loss figures obtained by different loss prediction schemes with measured no-load losses. Second, we examine the predicted net effect of bidirectional flux, i.e., the rotational loss. We show that the average degree of rotation in the stator core, and hence the rotational loss, is closely related to the stator slot geometry.

  • 47.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall AB, Älvkarlebylaboratoriet, Älvkarleby, Sweden.
    Dahlbäck, Niklas
    Vattenfall AB, Älvkarlebylaboratoriet, Älvkarleby, Sweden.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Power system flexibility need induced by wind and solar power intermittency on time scales of 1-14 days2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, p. 339-344Article in journal (Refereed)
    Abstract [en]

    This article describes a method to assess the needed production flexibility to adapt the power system to the production from variable renewable energy sources such as wind power and photovoltaics over time horizons of 1-14 days. Load and production data from the German power system is used to quantify the flexibility need in terms of power and energy storage requirement due to higher shares of renewable energy (20-80%). It is found that with an 80% variable renewable energy share in the German system, the average power need from flexible sources decreases by 31 GW (59%) while the peak power need only decreases by 3 GW (4%). In terms of energy, the storage need over a two week horizon increases by 2.6 TWh, which is 14% of the average load per day. If the European plans for 100 GW wind power in the North Sea region are realised, this would mean an increase of the energy storage need in the region with 2.2 TWh over a two week horizon.

  • 48.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Field Measurements and System Identification of Three Frequency Controlling Hydropower Plants2015In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 30, no 3, p. 1061-1068Article in journal (Refereed)
    Abstract [en]

    The dynamic behaviour of hydropower plants participating in primary frequency control is investigated in this paper through frequency response, step response and setpoint change tests on three Swedish hydropower plants. Grey-box system identification is used to estimate the parameters of simple linear models suitable for power system analysis and the major shortcomings of the linear models are discussed. It is found that frequency response tests with sinusoidal input signals give more reliable information about the dynamics of the plants than step response tests. It is also shown that backlash in the runner and guide vane regulating mechanisms are of great importance for the dynamic behaviour of the plants, and that the incremental gain from guide vane opening to power varies considerably with the operation point.

  • 49.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Agneholm, Evert
    Gothia Power, Gothenburg, Sweden..
    Westberg, Andreas
    Svenska Kraftnat, Sundbyberg, Sweden..
    Full-scale test and modelling of the frequency control dynamics of the Nordic power system2016In: 2016 IEEE POWER AND ENERGY SOCIETY GENERAL MEETING (PESGM), New York: IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    The grid frequency quality in the Nordic power system has been deteriorating during the last decade. To improve the situation, a better understanding of the system is needed. In this paper, a model of the Nordic power system dynamics with respect to normal operation frequency control is set up and compared with full-scale measurements on the system. The "60 s oscillation" of the grid frequency is measured and explained by the system model.

  • 50.
    Saarinen, Linn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Vattenfall Hydropower AB, SE-81470 Alvkarleby, Sweden.
    Norrlund, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Alvkarlebylaboratoriet, Vattenfall Res & Dev, SE-81426 Alvkarleby, Sweden.
    Yang, Weijia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Allocation of Frequency Control Reserves and its Impact on Wear and Tear on a Hydropower Fleet2018In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 33, no 1, p. 430-439Article in journal (Refereed)
    Abstract [en]

    Power systems are making a transition from purely technical, centrally planned systems to market based, decentralized systems. The need for balancing power and frequency control reserves are increasing, partially due to variable renewable production, which gives an opportunity for new incomes but also a challenge in terms of changed modes of operation with risk for reduced lifetime for controllable power plants. This paper investigates how the allocation of a sold volume of frequency control reserves within a large hydropower production fleet can affect the costs of providing primary and secondary reserves, in terms of its impact on wear and fatigue, production losses, and the quality of the delivered frequency control. The results show that for primary control, low static gain in the governors results in poor quality and a large amount of load cycles of the units. High static gain, on the other hand, increases the production losses. The control work of the fleet can be reduced by using a proper balance of primary and secondary control gain on each unit, although the intuitive results from linear models exaggerate this effect. Automatic secondary control improves the system frequency quality but also increases the wear.

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