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  • 101.
    Solum, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Investigating the overload capacity of a direct-driven synchronous permanent magnet wind turbine generator designed using high-voltage cable technology2007In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 31, no 11, p. 1076-1086Article in journal (Refereed)
    Abstract [en]

    Utilization of wind energy to maximum permissible limits for generating electrical power has become necessary to meet the global energy demands. Under such circumstances the present day conventional wind turbine generators pose a limitation regarding the overload capability, specifically significant when they need to operate in high-energy wind conditions. It is proposed that by employing a completely different generator winding concept, based on high-voltage cable technology, to a specific generator, it is possible to increase the generator overload capabilities and thereby making it operationally efficient in high wind speed situations. Therefore, the possibility of extracting more energy is predicted to increase. Simulations, based on finite-element methods combined with external circuit models for the generator, have been performed. The results demonstrate that under given thermal and electrical restrictions, a direct-driven permanent magnet synchronous wind turbine generator, based on high-voltage cable windings, is capable of being overloaded more than twice the rated power, thus making it very suitable for strong wind situations.

  • 102. Sonnadara, Upul
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Characteristics of cloud-to-ground lightning flashes over Sweden2006In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 74, no 5, p. 541-548Article in journal (Refereed)
    Abstract [en]

    A detailed study of the characteristics of cloud-to-ground (CG) lightning flashes over Sweden was carried out for the period 1987-2000 using data obtained from the Swedish lightning-locating network. Results are presented by analysing over half a million lightning ground flashes. The average variation of the annual mean of the total number of flashes was found to be 37%. About 12% of the CG flashes were positive flashes and their average variation about the annual mean was 26%. The average peak currents were fairly constant over the years with variations as little as 4% for negative flashes and 5% for positive flashes. The average peak current values for negative and positive flashes were -29.90 and +63.97 kA respectively. A correlation between the mean monthly flash count and percentage of positive flashes was seen. A similar relationship is seen with the mean monthly flash count and the peak currents for both polarities. In general, high flash density and high peak currents were observed in the southern part of Sweden where most of the major cities are located. Flash densities exceeding 0.4 flashes km(-2) were observed for several large cities. The maximum flash rate of 32 flashes h(-1) within a 10 km radius was seen in Jonkoping (14.18 degrees E, 57.78 degrees N) in the province of Smaland.

  • 103.
    Stålberg, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Waters, Rafael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Full-Scale Testing of PM Linear Generator for Point Absorber WEC2005In: Proceedings of the 6th European Wave and Tidal Energy Conference, 2005Conference paper (Refereed)
  • 104.
    Söderström, Daniel
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Baránková, Hana
    Bárdos, Ladislav
    Modelling the Dynamics of a Pulsed Atmospheric Plasma in Hollow Electrode GeometryIn: Journal of Physics D: Applied PhysicsArticle in journal (Refereed)
  • 105.
    Söderström, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Baránková, Hana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bárdos, Ladislav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On Dimensions of Atmospheric-Pressure Hollow Cathodes2007In: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 35, no 3, p. 522-526Article in journal (Refereed)
    Abstract [en]

    The hollow cathode is known as a source of high-density plasmas. This property is due to the hollow-cathode effect (HCE), which can be explained by the oscillations of fast electrons between repelling potentials of opposing space-charge sheaths. At atmospheric pressure, one should be able to create an HCE by adjusting the dimension of the hollow cathode. Experiments show that the dimensions could be as large as 500, so that the sheath thickness may be on the order of 100. Theoretical models of the atmospheric-pressure sheaths based on the conventional Child-Langmuir approach give the sheath thicknesses on the order of 10, which contradicts the experiments. We introduce here a new model which takes into account three groups of electrons: slow, fast, and secondary. By adding a group of fast and secondary electrons, we show that the sheath thickness increases as compared with only slow electrons present.

  • 106.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    On the representation of the lightning return stroke process as a current pulse propagating along a transmission line2005In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 20, no 2, p. 823-837Article in journal (Refereed)
    Abstract [en]

    Assuming that the representation of the lightning return stroke as a current pulse propagating along a transmission line is valid, the effects of different transmission line parameters both on the channel current and the electromagnetic fields are investigated. The transmission line parameters that are incorporated into the study are the spatial variation of the inductance and the capacitance, the channel resistance and its temporal variation and the finite conductance of the line. The results show that the introduction of the time varying channel resistance and the finite conductance will change the predictions of the model in such a direction that they will come closer to the experimental observations.

  • 107.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Representation of the return stroke as a transmission line: the apparent return stroke velocity2004In: Proceedings of International Conference on Lightning Protection, Avignon, France, 2004, 2004Conference paper (Refereed)
  • 108.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    On the influence of conductor heights and lossy ground in multi-conductor transmission lines for lightning interaction studies in railway overhead traction systems2004In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 71, no 2, p. 186-193Article in journal (Refereed)
    Abstract [en]

    Railway overhead traction system is a classic example of scattered conductor configuration, where tracks and other wires form multi-conductor transmission lines (MTLs) with large variation in conductor heights above ground and they are spread across regions having different soil conditions. Lightning transient analysis in such systems has not received much attention earlier. Here we analyze the influence of conductor heights and lossy ground on the induced voltages in a two conductor MTLs for the case of a direct lightning strike. For transient analysis, modified time domain transient ground impedance expressions having better early and late time behavior was used. The dependence of transient ground impedance on conductor heights and ground resistivity are presented and discussed. The early time transient ground impedances are unaffected by ground resistivity but their decaying nature is highly dominated by ground resistivity. It is found, if one of the conductors is close to ground (a rail) and if it is at large vertical distance from struck conductor (an auxiliary power line), then with increasing ground resistivity the peak induced voltages in the conductor close to ground initially increase, then decrease and finally tend to remain constant (within 100-10,000Ωm). This phenomenon is opposite to that compared to conductors that are close to each other with minimum vertical separation (two auxiliary power lines), where the peak induced voltages increase with increasing ground resistivity. The study focuses mainly to access when a mutual coupling due to system geometry or due to ground losses becomes dominant in determining induced effects from lightning in MTLs, which could be an important contribution to the lightning interaction studies for electrified railway systems.

  • 109.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montaño, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lindeberg, P. A.
    Hellström, U.
    Measurements of Lightning Transients Entering a Swedish Railway Facility2004In: Proceedings of 27th International Conference on Lightning Protection, 2004Conference paper (Other academic)
  • 110.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Mazloom, Ziya
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Technique for Reducing Transient Voltages in Multiconductor-Shielded Cables2007In: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 49, no 2, p. 434-440Article in journal (Refereed)
    Abstract [en]

    It is a common practice that the unused pairs (inactive conductors) in shielded cables are left open (open circuited at the terminal block) in telecommunication systems. In this paper, it is shown by both theory (based on transmission line analysis) and experiments that if those inactive conductors are shorted to the cable shield, then the transient voltages on the other active conductors (conductors in service) can be reduced when external transients/faults due to lightning or switching couple to the shield. This could be a good EMC practice for transient voltage reduction in telecommunication systems.

  • 111.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Pulse Propagation in Underground Wires-A Transmission Line Analysis2005Conference paper (Other academic)
  • 112.
    Theethayi, Nelson
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Yirdaw, Tegegne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, Raul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Experimental Investigation of Lightning Transients Entering a Swedish Railway Facility2007In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 22, no 1, p. 354-363Article in journal (Refereed)
    Abstract [en]

    Transients caused by lightning in railway facilities have not received much attention. In this paper, we describe the measurements of lightning transients entering a Swedish railway facility during the summer of 2003. The measurements of the transients were made in a technical house that provides an uninterrupted power supply for telecommunication systems and the signal systems. An analysis of the data has shown that transients in excess of 7 kV (peak to peak) can appear across the line-to-neutral supply system due to an indirect lightning strike. Some typical characteristics of the line-to-neutral transient voltages in terms of stroke locations and stroke amplitudes are presented. Further, from the experimental data, an empirical relation for predicting the line-to-neutral transient voltage in terms of stroke location and stroke current amplitude is obtained. Simple induced voltage calculations are presented to identify the levels of induced voltages appearing at the input of the technical house. The influence of ground conductivity on those induced voltages is also presented. The information presented in the paper is an important electromagnetic-compatibility issue associated with the lightning protection for railway systems.

  • 113.
    Thorburn, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wave energy transmission system concepts for linear generator arrays2004In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 31, no 11-12, p. 1339-1349Article in journal (Refereed)
    Abstract [en]

    Wave energy is a renewable source, which has so far not been exploited widely. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. This article presents a range of systems with point absorbers on the surface and linear generators placed on the seabed, converting the wave motion into electrical power. Electrical power components are combined in different ways to obtain solutions suitable for various conditions. Different topologies for the electrical system transmitting power to the grid are discussed. Qualitative case studies are used to exemplify system options and connection schemes.

  • 114.
    Thorburn, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Karlsson, Karl Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wolfbrandt, Arne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Time stepping finite element analysis of variable speed synchronous generator with rectifier2006In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 83, no 4, p. 371-386Article in journal (Refereed)
    Abstract [en]

    Several applications for renewable energy conversion make use of variable speed generators. A conversion from variable frequency to grid frequency is therefore essential. One part of the converter is a rectifier. A rectifier model is presented, which is integrated in a time stepping finite element simulation environment where the generator and circuit equations are solved simultaneously. The model handles bidirectional alternator speeds as the application is a linear generator for ocean wave energy conversion. The rectifier model is extended with a load model, consisting of R, L and E, and simulations show what impact the rectifier has on the generator’s behaviour.

  • 115.
    Thorburn, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Analytical and circuit simulations of linear generators in farm2006In: Transmission and Distribution Conference and Exhibition, 2005/2006 IEEE PES, 2006, p. 495-500Conference paper (Refereed)
    Abstract [en]

    Wave energy is an emerging kind of renewable energy, and several energy conversion methods are available today. One solution is to connect a buoy to a linear generator. Such units are quite small (10-100 kW), and farm solutions are suggested to increase power production. This paper shows the results from small farm simulations where the alternator motion is varied for the generators in the farm

  • 116.
    Thorburn, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Case study of upgrading potential for a small hydro power station2005In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 30, no 7, p. 1091-1099Article in journal (Refereed)
    Abstract [en]

    Schemes for upgrading hydro power are formed in many parts of the world. Small hydro power (<15 MW) constitutes a fraction of all hydro power, but upgrading can still be worthwhile. In this article, a small generating station in Sweden, with two generators, is simulated with new generators. The voltage is increased by introducing a cable wound stator, thereby the transformers can be excluded, and more efficient generators are introduced with a higher power factor. These improvements lead to an active power increase from 8.9 to 9.4 MW per generator, which means an increased total annual production by 4.2 GW h.

  • 117.
    Thorburn, Karin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Nilsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Generators and electrical systems for direct drive energy conversion2006Conference paper (Refereed)
  • 118.
    Thottappillil, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lightning strikes to tall towers with implications to electromagnetic interference2005In: Proceedings of RadioVetenskap och Kommunikation (RVK 05), Linkoping, Sweden, 2005, 2005, p. 465-470Conference paper (Refereed)
  • 119.
    Thottappillil, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Yaqing
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, Michael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lindeberg, Per Anders
    Hellström, Ulf
    Computer simulation model for Swedish railway system for evaluating the effects of lightning and EMI2003In: Proceedings of the World Congress on Railway Research, 2003Conference paper (Refereed)
  • 120.
    Thottappillil, Rajeev
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Uman, Martin
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Electric and magnetic fields from a semi-infinite antenna above a conducting plane2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 61, no 3-4, p. 209-221Article in journal (Refereed)
    Abstract [en]

    The electric and magnetic field structures around a semi-infinite thin-wire antenna vertically placed above a perfectly conducting ground plane are investigated when the antenna is supporting two different types of sources. It is shown that when the wire is carrying a uniform line charge, the electrostatic potentials are equal on the surfaces of imaginary cones of fixed cone angles with axis along the wire and apex at the conducting plane. The electrostatic field vectors are shown to be perpendicular to the imaginary cones and tangential to the meridian lines of half-spherical shells centered at the base of the line charge. The vertical components of the electrostatic field on the surface of these imaginary half-spherical shells of a given radius are constant, except at the wire itself. The magnetic field structure associated with a constant current in the semi-infinite antenna is that of an infinite wire. The electric and magnetic fields due to a time-varying charge or current pulse propagating with the speed of light along the vertical thin-wire antenna have a spherical transverse electromagnetic (TEM) field structure, identical to that for the case of a uniform line charge and a uniform current. The connection between the static and dynamic solutions is derived mathematically using two different approaches.

  • 121.
    Tyrberg, Simon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Offshore Surveillance of Wave Buoys2007Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To gain further knowledge about the motion of the wave buoys involved in the Islandsberg project for wave power, a surveillance system has been designed. The base for the system consists of a lattice tower to be placed on one of two islets southwest of Lysekil: Klammerskären. The distance from the islets to the wave energy research park and the wave buoys is between 150 and 300 meters. The tower will be 12 meters high and in it a network camera will be mounted, together with a small wind turbine, two solar panels, a battery bank and equipment for communication with land. A signal cable presently dispatched in the sea near Klammerskären will be used to connect the islets to a measuring station at the nearby island of Gullholmen. All the necessary permits for the project have been acquired, all of the equipment to be used has been delivered, and the full procedures for the construction and installation of the tower and the surveillance system have been laid out. The tower however, has not yet been mounted and the system has not been tested as a whole. When completed, the tower may be used as a station for further measurements within the Islandsberg project.

  • 122.
    Vernon, Cooray
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    NOx production in lightning flashes2007In: International Conference on Atmospheric Electricity, ICAE, Beijing, China, 2007Conference paper (Other academic)
  • 123. Waters, Rafael
    et al.
    Stålberg, Magnus
    Danielsson, Oskar
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Svensson, Olle
    Gustafsson, Stefan
    Strömstedt, Erland
    Eriksson, Mikael
    Sundberg, Jan
    Leijon, Mats
    First experimental results from sea trials of a novel wave energy systemIn: Applied Physics LetterArticle in journal (Refereed)
  • 124.
    Waters, Rafael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Stålberg, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Svensson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Gustavsson, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Strömstedt, Erland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sundberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Experimental results from sea trials of an offshore wave energy system2007In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, no 3, p. 034105-Article in journal (Refereed)
    Abstract [en]

    A full-scale prototype of a wave power plant has been installed off the Swedish west coast and the overall wave energy converter concept has been verified. Initial results have been collected and significant insights discovered. Energy absorption dependency on load as well as output voltage and power is demonstrated. It is shown that great overload capability of the directly driven linear generator is critical, and indicated that, for resistive loads, optimal load does not vary with wave climate. Future grid supplying energy production would necessitate parks of wave power plants in order to reduce power fluctuations.

  • 125.
    Wejander, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    En vindkraftparks inverkan på Gävle Energis elnät2010Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The effects from a planned wind farm on the grid utility Gävle Energis electrical grid have been studied. The wind farm is planned to be built in the forest 15 km north of Gävle and will have 23 turbines with rated power from 2 to 2.5 MW, resulting in a total installed power between 46 MW and 57.5 MW. The grid connection will be made at 70 kV. The aim of the analysis was to determine what effects the wind farm would have on the power grid in the form of electrical disturbances (flicker etc.), need for new investment and raised operational cost. To allow the connection of the wind farm technical solutions (new lines, power stations and grid reinforcements) have been constructed. The effects and need for further investment if a larger wind farm is built have also been studied. Calculations of the electrical noise where made, using data for 5 different wind turbines, and compared to the maximum allowable levels. Connections using both overhead lines and cables where studied. The majority of costs used in the economical analysis where taken from EBR:s widely used cost catalogue. The analysis shows that 57.5 MW can be installed with all the turbine models. The need for new investment depends on the line used but is in the range of 38.300.000 SEK to 61.100.000 SEK. Up to 63 MW can be installed without any further investment and up to 98 MW if further investment is made.

  • 126.
    Wolfbrandt, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Automated Design of a Linear Generator for Wave Energy Converters - A Simplified Model2006In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 42, no 7, p. 1812-1819Article in journal (Refereed)
    Abstract [en]

    An encouraging way to convert ocean wave energy into electricity through direct drive is by using a linear, synchronous, longitudinal-flux permanent-magnet machine (LFM), where the piston is driven by a buoy. In this paper, the speed of the piston is assumed to be constant or sinusoidal. The paper presents an automated method for optimizing the design variables of an LFM with a rectifier, using time-stepping finite-element analysis. The method yields feasible LFM designs tailored to a given ocean wave climate, assuming constant or sinusoidal piston speed. The method will help to avoid a large amount of field calculations to obtain an optimal LFM driven by a buoy. The systematic approach results in a transparent investigation, giving the engineer an easy way to determine the best design. The paper presents LFM designs for a calm site in the Baltic Sea as examples.

  • 127.
    Zitnik, Mihael
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Numerical Modelling of Transients in Electrical Systems2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with the numerical modelling of the response of electrical systems to transient surge voltages and currents caused by lightning. Electrical systems, when subjected to high amplitude transients behave in ways very different from its behaviour under normal operating conditions. Modelling the response of the system in a computationally efficient way, while maintaining sufficient accuracy, is the challenge being addressed in this thesis.

    While modelling transients in a complex system it is required to reduce the complexity of the system in the model to manageable levels, at the same time retaining all the important characteristics of the system, including the non-linear responses. Transmission line model in time domain is simple and can handle non-linearities easily. Therefore transmission line method is utilised for modelling complex systems in this thesis. Transmission line parameters are deduced from the geometry of the system using field simulation methods. The model is then implemented in a circuit simulation software.

    To enable computer modelling of transient protection, experiments were conducted on metal-oxide varistors and the results were compared with the predictions of the existing varistor models. From these comparisons the deficiency of existing varistor models are identified and a new improved varistor model is proposed that can overcome these deficiencies. Additionally, using the transmission line method a multiconductor cable model is developed and experimentally verified.

    Several practical problems of industrial importance are investigated using the transmission line modelling method. The co-ordination between the primary and secondary overvoltage protectors in a low voltage power installation is investigated and it is shown that the existing practice of co-ordinating the primary and secondary protectors based only on the current and voltage ratings do not always work. In another application of the method current and voltage distributions during a lighting strike to the railway signalling and traction system is determined. Lastly, simulation of direct lightning strike to a radio communication tower is performed and the division of current between the cable system and the tower construction is determined. The parameters that influence this current division are also determined.

  • 128.
    Ågren, Olov
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Moiseenko, V. E.
    On MHD stability, ellipticity, omnigenuity, constants of motions and a modified thermal barrier of a straight field line mirror2007In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 51, no 2T, p. 200-203Article in journal (Refereed)
    Abstract [en]

    The straight field line mirror field(1) is the unique field which gives the lowest ellipticity of the flux tube of an MHD stable minimum B mirror field. In this particular vacuum field, each gyro center bounces back and forth on a single magnetic field line, and a pair of two new constants of motion is associated with this property(2). Using these invariants in the Vlasov equation, it can be shown that the radial gyro center magnetic drift is absent to first order in the plasma beta, and the equilibrium is omnigenous. The neoclassical increase of the radial transport may thus be avoided without an axisymmetrization of this single cell mirror. A scheme to improve end confinement of ions, and simultaneously create an electric potential barrier for the electrons and a sloshing ion component, has been proposed. The end plugging transforms ions under way to escape into the loss cone into sloshing ions by ion cyclotron resonance heating. Numerical studies on sloshing ion production by RF heating(4) demonstrate strong absorption of the RF field near the fundamental gyro frequency resonance of the minority deuterium ions as well as near the tritium second harmonic gyro frequency resonance. The scenario indicates a possibility to achieve a high energy gain factor in this kind of single cell mirror with the proposed modified thermal barrier.

  • 129.
    Ågren, Olov
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Moiseenko, V. E.
    Noack, K.
    Hagnestål, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Possibilities for transmutation of nuclear waste and energy production with a "straight field line mirror" neutron source2009In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 55, no 2T, p. 46-51Article in journal (Refereed)
    Abstract [en]

    A pure fusion mirror device suffers from the predicted low values of the Q factor (energy gain factor). A much higher energy production may be achieved in a fusion-fission reactor, where the fusion plasma neutron source is surrounded by a fission mantle. The fusion neutrons are capable of initiating energy producing fission reactions in the surrounding mantle. A mirror machine can probably be designed to provide sufficient space for a 1.1 m wide fission mantle inside the current coils, and the power production from the fission reactions can in such a case exceed the fusion power by more than two orders of magnitude ( P-fis / P-fus approximate to 150), suggesting a realistic reactor regime for a mirror based fusion-fission device. An energy producing device may operate with an electron temperature around 1 keV Transmutation of long-lived radio active isotopes (minor actinides) from spent nuclear fuel from fission reactors can reduce geological storage from 100 000 years to only 300 years. Since the energy of D-T fusion neutrons are above the threshold for the most important transmutation reactions desired for treatment of nuclear waste, there may be an interest for a mirror transmutation device even if no net energy is produced. Recent theoretical simulations have considered the possibility to use the Gas Dynamic Trap (GDT) at Novosibirsk as a subcritical burner for transmutation by fusion neutrons. In the present work, possibilities for mirror based fusion-fission machines are discussed Means to achieve sufficient end confinement for a straight field line mirror fusion-fission system with a thermal barrier are briefly analyzed End leakage can alternatively be avoided by connecting the ends of a magnetic mirror with a stellerator tube, while the fusion neutrons are produced in the mirror part where a high energy sloshing ion component is confined. A zero dimensional model for such a mirror-stellarator system has been developed. The computed results indicate some possible parameter regimes for industrial transmutation and power production.

  • 130. Ågren, Olov
    et al.
    Moiseenko, Vladimir
    Johansson, Cecilia
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Gyro center invariant and associated diamagnetic current2005In: Physics of Plasmas, Vol. 12, no 12, p. 122503-1-122503-13Article in journal (Refereed)
  • 131. Ågren, Olov
    et al.
    Moiseenko, Vladimir
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Constants of motion in a minimum B mirror magnetic field2005In: Physical Rewiev E, Vol. 72, no 2, p. 026408-1-026408-5Article in journal (Refereed)
  • 132. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Magnetic mirror minimum B field with optimal ellipticity2004In: Physics of Plasmas, Vol. 11, no 11, p. 5041-5045Article in journal (Refereed)
  • 133. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Minimum B field with optimal ellipticity and idea for improved axial confinement by tuned ICRH cycles2005In: Transactions of Fusion Science and Technology, ISSN 1536-1055, Vol. 47, no 1T, p. 285-287Article in journal (Refereed)
  • 134. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rigid rotation symmetry of a marginally stable minimum B field and analytical expressions of the flux coordinates2005In: Physics of Plasmas, Vol. 12, no 4, p. 042505-1-042505-5Article in journal (Refereed)
  • 135. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sloshing ion distribution function in a minimum B mirror field2005In: Physics of Plasmas, Vol. 12, no 2, p. 022504-1-022504-5Article in journal (Refereed)
  • 136. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theoretical study of increased electron temperature in mirror machines by tuned ion cyclotrin resonance heating cycles2005In: Physics of Plasmas, Vol. 12, no 2, p. 022506-1-022506-10Article in journal (Refereed)
  • 137. Ågren, Olov
    et al.
    Savenko, Natalia
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Theory of the staight field line mirror2005In: Conference Proceedings of the 32nd EPS Plasma Physics Conference in Tarragona, Spain, Vol. 29C, p. P. - 4.069Article in journal (Refereed)
123 101 - 137 of 137
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