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  • 1.
    Akyuz, Mose
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Positive streamer discharges in air and along insulating surfaces: experiment and simulation2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The power quality of modern society relies on the electrical properties of the dielectric insulators used in the power industry. Much research work has been conducted with an aim to understand and predict the insulating behaviour of such materials under different kinds of atmospheric conditions, but still there are many unsolved problems. In particular, there is a lack of knowledge concerning the electrohydrodynamic and electrophysical processes at the insulator surface and the surrounding medium. No detailed knowledge exists at present of the processes governing the development of electrical discharges along the surface of insulators.

    With an aim to enhance the knowledge in this field in general and on the electrical performance of outdoor insulators in particular a detailed study of the positive streamer discharges in air and along dielectric surfaces was conducted. The study was also extended to gain more knowledge on the water drop initiated electrical discharges in air and the attachment of natural lightning flashes to a Franklin conductor.

    In the first phase, the study was focused on positive streamer discharges propagating in air. The spatial distribution of the charge of a branched streamer discharge was obtained and the charge contained in a single streamer branch was quantified. In the second phase measurements and simulations of streamer discharges propagating along insulating surfaces were conducted with an aim to understand how the insulating surfaces interact with streamer discharges. In addition to quantifying the parameters of streamer discharges propagating along insulating surfaces, the results of these studies made it possible to separate and quantify the effects of the dielectric constant and the surface properties on the streamer discharges. In the third phase a comprehensive computer algorithm was developed to simulate 3-dimensional propagation of positive streamer discharges in air and along dielectric surfaces taking into account the branching effect.

    The conditions necessary for the initiation of streamer discharges were applied to obtain the minimum strength of the background electric field required to initiate electrical discharges in the presence of water drops. In particular the study provided an explanation of how lightning flashes are initiated in thunderclouds in background electric fields as low as 200 kV/m. Finally, the study was extended to understand the performance of lightning conductors paying special attention to the influence of conductor radius and the streamer inception criterion.

  • 2.
    Akyuz, Mose
    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.
    Larsson, Anders
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Franke, Axel
    Characteristics of Laser-triggered Electric Discharges in Air2005In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 12, no 5, p. 1060-1070Article in journal (Refereed)
  • 3. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    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.
    Channel tortuosity of long laboratory sparks2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 8, p. 521-526Article in journal (Refereed)
    Abstract [en]

    Channel tortuosity of 50 cm long laboratory sparks were measured by analyzing a set of images taken by three cameras. The cameras were placed at a radial distance of 200 cm from the spark gap. The angle between any two cameras was 120 degrees. The sparks were generated between a steel rod and. a plane electrode. The distribution of the direction change of the channel was found to be Gaussian with a standard deviation of 15.3 degrees. The average tortuosity of the channel defined as the mean absolute value of the direction change was 11.8 +/- 1.4 degrees, which is smaller than the average tortuosity of natural lightning and close to the tortuosity of triggered lightning. The average tortuosity is dependent on the segment length used in calculating the direction change. A gradual increase in the average tortuosity (0.08 degrees/cm) was seen when the sparks propagated towards the plane electrode.

  • 4. Amarasinghe, Dulan
    et al.
    Sonnadara, Upul
    Berg, Marcus
    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.
    Correlation between brightness and channel currents of electrical discharges2007In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 14, no 5, p. 1154-1160Article in journal (Refereed)
    Abstract [en]

    Channel brightness of 500 mm long electrical discharges were measured by analyzing a set of digitized images taken by 3 cameras placed symmetrically around a discharge gap at a radial distance of 200 cm from the axis of the spark. The sparks were generated between a steel rod and a plane electrode. The distribution of the brightness across the channel represented a Gaussian distribution. A linear correlation was seen between the channel brightness measured by different cameras looking at the same spark channel. No correlation was seen between the channel brightness and the channel depth (direction perpendicular to the camera plane). The measured peak current and the brightness of the main spark channel show a high degree of correlation (R-2=0.97). The sum of brightness of branches was equal to the brightness of the parent channel. One can use this result to calculate the relative distribution of branch currents in complex electrical discharges including natural lightning flashes. If the current in the parent channel is known, branch currents can be calculated by measuring the optical intensities using photographic techniques.

  • 5.
    Anatory, Justinian
    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.
    Kissaka, Mussa
    Faculty of Electrical and Computer Systems Engineering, University of Dar es Salaam.
    Mvungi, Nerey
    Faculty of Electrical and Computer Systems Engineering, University of Dar es Salaam.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The effects of load impedance, line length, and branches in the BPLC transmission-lines analysis for-medium-voltage channel2007In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 22, no 4, p. 2156-2162Article in journal (Refereed)
    Abstract [en]

    This paper presents the effects of load impedance, line length and branches on the performance of medium-voltage power-line communication (PLC) network. The power-line network topology adopted here is similar to that of the system in Tanzania. Different investigation with regard to network load impedances, direct line length (from transmitter to receiver), branched line length and number of branches has been investigated. From the frequency response of the transfer function (ratio of the received and transmitted signal), it is seen that position of notches and peaks in the magnitude and phase responses are largely affected in terms of attenuation and dispersion by the above said network parameters/configuration. These are observed in the time domain responses too. The observations presented in the paper could be helpful in suitable design of the PLC systems for a better data transfer and system performance.

  • 6.
    Anatory, Justinian
    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.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Kissaka, Mussa
    Faculty of Electrical and Computer Systems Engineering, University of Dar es Salaam.
    Mvungi, Nerey
    Faculty of Electrical and Computer Systems Engineering, University of Dar es Salaam.
    The Effects of Load Impedance, Line Length, and Branches in the BPLC—Transmission-Line Analysis for Indoor Voltage Channel2007In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 22, no 4, p. 2150-2155Article in journal (Refereed)
    Abstract [en]

    This paper presents the effects of load impedance, line length and branches on the performance of an indoor voltage broadband power line communications (BPLC) network. The power line network topology adopted here is similar to that of the system found in Tanzania. Different investigations with regard to network load impedances, direct line length from transmitter to receiver, branched line length, and number of branches has been carried out. From the frequency response of the transfer function (ratio of the received and transmitted signal), it is seen that position of notches and peaks in the magnitude and phase responses are largely affected by the above said network parameters/configuration, mainly in terms of attenuation and dispersion. These effects are observed in the time domain responses also. The observations presented in the paper could be helpful in the suitable design of the BPLC systems for a better data transfer and system performance.

  • 7.
    Baránková, Hana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bárdos, Ladislav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Söderström, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cold Atmospheric Plasma in Nitrogen and Air Generated by the Hybrid Plasma Source2006In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 24, no 4, p. 1410-1413Article in journal (Refereed)
    Abstract [en]

    Generation of long plumes of cold atmospheric plasma in nitrogen and air has been successfully performed by the hybrid hollow electrode activated discharge (H-HEAD) source. The source with a simple cylindrical electrode terminated by a gas nozzle combines the microwave antenna plasma with the hollow cathode plasma generated inside the gas nozzle by pulsed dc power. The H-HEAD source is capable of generating up to 10 cm long plumes in air at microwave powers below 500 W and at air flow rates as low as 100 sccm (standard cubic centimeter per minute). The corresponding flow rates in the nitrogen plasma are even less than 80 sccm. The discharges in air and nitrogen have similar shapes and are comparable with the corresponding plasma columns in argon. A comparison of the optical emission spectra of the plasma in nitrogen and air is presented. The temperatures generated on steel substrates by interaction with nitrogen and air plasma columns at different microwaves and dc powers are compared with the corresponding effects in argon plasma.

  • 8.
    Baránková, Hana
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bárdos, Ladislav
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Söderström, Daniel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Gustavsson, Lars-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Characterization of Hybrid Atmospheric Plasma in Air and Nitrogen2006In: SVC, Society of Vacuum Coaters: 49th Annual Technical Conference Proceedings, 2006, p. 41-43Conference paper (Refereed)
  • 9.
    Becerra, Marley
    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.
    A self-consistent upward leader propagation model2006In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, no 16, p. 3708-3715Article in journal (Refereed)
    Abstract [en]

    The knowledge of the initiation and propagation of an upward moving connecting leader in the presence of a downward moving lightning stepped leader is a must in the determination of the lateral attraction distance of a lightning flash by any grounded structure. Even though different models that simulate this phenomenon are available in the literature, they do not take into account the latest developments in the physics of leader discharges. The leader model proposed here simulates the advancement of positive upward leaders by appealing to the presently understood physics of that process. The model properly simulates the upward continuous progression of the positive connecting leaders from its inception to the final connection with the downward stepped leader (final jump). Thus, the main physical properties of upward leaders, namely the charge per unit length, the injected current, the channel gradient and the leader velocity are self-consistently obtained. The obtained results are compared with an altitude triggered lightning experiment and there is good agreement between the model predictions and the measured leader current and the experimentally inferred spatial and temporal location of the final jump. It is also found that the usual assumption of constant charge per unit length, based on laboratory experiments, is not valid for lightning upward connecting leaders.

  • 10.
    Becerra, Marley
    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.
    A simplified physical model to determine the lightning upward connecting leader inception2006In: IEEE Transactions on Power Delivery, ISSN 0885-8977, Vol. 21, no 2, p. 897-908Article in journal (Refereed)
  • 11.
    Becerra, Marley
    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.
    Time dependent evaluation of the lightning upward connecting leader inception2006In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, no 21, p. 4695-4702Article in journal (Refereed)
    Abstract [en]

    The evaluation of the upward connecting leader inception from a grounded structure has generally been performed neglecting the effect of the propagation of the downward stepped leader. Nevertheless, field observations suggest that the space charge produced by streamer corona and aborted upward leaders during the approach of the downward lightning leader can influence significantly the initiation of stable upward positive leaders. Thus, a physical leader inception model is developed, which takes into account the electric field variations produced by the descending leader during the process of inception. Also, it accounts for the shielding effect produced by streamer corona and unstable leaders formed before the stable leader inception takes place. The model is validated by comparing its predictions with the results obtained in long gap experiments and in an altitude triggered lightning experiment. The model is then used to estimate the leader inception conditions for free standing rods as a function of tip radius and height. It is found that the rod radius slightly affects the height of the downward leader tip necessary to initiate upward leaders. Only an improvement of about 10% on the lightning attractiveness can be reached by using lightning rods with an optimum radius. Based on the obtained results, the field observations of competing lightning rods are explained. Furthermore, the influence of the average stepped leader velocity on the inception of positive upward leaders is evaluated. The results obtained show that the rate of change of the background electric field produced by a downward leader descent largely influences the conditions necessary for upward leader initiation. Estimations of the leader inception conditions for the upper and lower limit of the measured values of the average downward lightning leader velocity differ by more than 80%. In addition, the striking distances calculated taking into account the temporal change of the background field are significantly larger than the ones obtained assuming a static downward leader field. The estimations of the present model are also compared with the existing leader inception models and discussed.

  • 12.
    Becerra, Marley
    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.
    Soula, Serge
    Chauzy, Serge
    Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no D12, p. D12205-Article in journal (Refereed)
    Abstract [en]

    Electric field measurements above ground have shown that the space charge layer created by corona at ground level shields the background electric field produced by the thundercloud. Therefore it is expected that this space charge layer can also influence the conditions required to initiate upward lightning from tall objects. For this reason, a numerical model that describes the evolution of the main electrical parameters below a thunderstorm is used to compute the space charge layer development. The time variation of the electric field measured at 600 m above ground during the 1989 rocket triggered lightning experiment at the Kennedy Space Center (Florida) is used to drive the model. The obtained space charge density profiles are used to compute the conditions required to initiate stable upward lightning positive leaders from tall towers. Corona at the tip of the tower is neglected. It is found that the space charge layer significantly affects the critical thundercloud electric fields required to initiate upward lightning leaders from tall objects. The neutral aerosol particle concentration is observed to have a significant influence on the space charge density profiles and the critical thundercloud electric fields, whereas the corona current density does not considerably affect the results for the cases considered in the analysis. It is found that a lower thundercloud electric field is required to trigger a lightning flash from a tall tower or other tall slender grounded structure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions.

  • 13.
    Berg, Marcus
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Estimation of hydrophobicity of insulating surfaces by studying sessile water drops2001Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today, the traditional insulator materials for high voltage powerlines, i.e. glass and porcelain, are gradually being replaced with new materials, most notably silicone rubber. One of the properties that make composite insulators based on silicone rubber attractive is their hydrophobicity, which in the laboratory can be estimated by measuring contact angles of sessile water drops. The hydrophobic surface gives composite insulators better electrical flashover characteristics than hydrophilic insulators when being wet or polluted. However, the hydrophobicity of insulators in service is degraded by many factors such as pollution deposits, surface arcing and ageing, and should therefore be checked regularly.

    In this thesis, image analysis of water drop patterns on an inclined flat polymeric insulator surface has been performed in order to find a simple mathematical function that indicates the level of hydrophobicity of the insulator surface. The result, given the name of "Average of Normalised Entropies", ANE, seems to correlate well with hydrophobicity as defined by the classification of the Swedish Transmission Research Institute. This function is a composition of three other functions, viz. the standard deviation, the Shannon entropy and the "fraction of small differences". All these are in turn based on the histogram of horizontal nearest-neighbour pixel differences for a given digital greyscale image of a water drop pattern. ANE is fairly independent of illumination intensity (exposure), electronic gain and offset, and also of limited changes in the surface inclination.

    It is known that the shape of water drops can enhance the local electric field and influence the initiation of electrical discharges on the insulator surface. In this thesis, a particularly simple form of the Young-Laplace equation governing the shape of a sessile drop is derived and augmented with measures that facilitate efficient numerical computation. This mathematical representation will be useful for simulating axisymmetric drops in a vertical electric field as well as for contact angle measurement methods based on fitting theoretical drop shapes to sessile drops in digital images.

  • 14. Berk, Herbert L.
    et al.
    Fisch, Nathaniel J.
    Burdakov, Alexander
    Dimov, Germadi I.
    Ivanov, Alexander A.
    Kruglyakov, Eduard P.
    Moiseenko, Vladimir
    Noack, Klaus
    Pastukhov, Vladimir P.
    Tanaka, Shigetoshi
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Scientists protest professor's dismissal2008In: Physics today, ISSN 0031-9228, E-ISSN 1945-0699, Vol. 61, no 12, p. 10-Article in journal (Refereed)
  • 15.
    Bernhoff, Hans
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    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 resources in sheltered sea areas: A case study of the Baltic Sea2006In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 31, no 13, p. 2164-2170Article in journal (Refereed)
    Abstract [en]

    Wave energy is a renewable source, which has not yet been exploited to a large extent. So far the main focus of wave energy conversion has been on the large wave energy resources of the great oceans on northern latitudes. However, large portions of the world potential wave energy resources are found in sheltered waters and calmer seas, which often exhibit a milder, but still steady wave climate. Examples are the Baltic Sea, the Mediterranean and the North Sea in Europe, and ocean areas closer to the equator. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. In the present work we instead focus on wave power plants consisting of a number of small wave energy converters, forming large arrays. In this context, we look at advantageous arrangements of point absorbers, and discuss the potential of the Baltic Sea as a case study.

  • 16.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Solum, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Perers, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lundström, Ludvig
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Lindblom, Adam
    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.
    Ericsson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Nilsson, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ivanova, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Danielsson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Eriksson, Sandra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bengtsson, H
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Isberg, Jan
    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.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Karlsson, K-E
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wolfbrandt, Ane
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    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.
    Rotating and Linear Syncronous Generators for Renewable Electric Energy Conversion: an Update of the Ongoing Research Projects at Uppsala University2004Conference paper (Other academic)
  • 17.
    Bolund, Björn
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Thorburn, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    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.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Upgrading Generators with new Tools and High Voltage Technology2004In: International journal on hydropower and dams, ISSN 1352-2523, Vol. 11, no 3, p. 104-108Article in journal (Refereed)
  • 18.
    Böhnke, Tobias
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Kratz, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Hultåker, Annette
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Köhler, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Edoff, Marika
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Roos, Arne
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ribbing, Carl-Gustaf
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Surfaces with high solar reflectance and high thermal emittance on structured silicon for spacecraft thermal control2008In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 30, no 9, p. 1410-1421Article in journal (Refereed)
    Abstract [en]

    Presented here is an examination of unstructured and structured (by anisotropic etching), monocrystalline silicon wafers coated with sputter deposited aluminum and chemical vapor deposited silicon dioxide for high solar reflectance and high thermal emittance, respectively. The topography of the samples was characterized with optical and scanning electron microscopy. Optical properties were examined with reflectance and transmittance spectroscopy, partly by usage of an integrating sphere. The measurement results were used to estimate the equilibrium temperature of the surfaces in space. The suitability of the surfaces with high solar reflectance and high thermal emittance to aid in the thermal control of miniaturized, highly integrated components for space applications is discussed. A silicon dioxide layer on a metal layer results in a slightly lower reflectance when compared to surfaces with only a metal layer, but might be beneficial for miniaturized space components and modules that have to dissipate internally generated heat into open space. Additionally, it is an advantage to microstructure the emitting surface for enhanced radiation of excess heat.

  • 19. Cooray, V.
    et al.
    Zitnik, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Manyahi, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Liu, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Physical Model of Surge-Current Characteristics of buried vertical Rods in the Presence of Soil Ionisation2002In: 26th International Conference on Lightning Protection, ICLP-2002, Cracow, Poland, September 2-6, Vol. 1, p357-362, 2002, Vol. 1, p. 357-362Conference paper (Refereed)
  • 20.
    Cooray, V.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Strandberg, G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rahman, M.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Montano, R.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Scuka, V.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A Novel Modification of the ’Transmission Line Model’ of Lightning Return Strokes2002In: 26th International Conference on Lightning Protection, ICLP2002, Cracow, Poland, September 2-6,                       Vol. 1, p50-55, 2002, Vol. 1, p. 50-55Conference paper (Refereed)
  • 21.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on radiation field pulses generated by cloud lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1397-1406Article in journal (Refereed)
    Abstract [en]

    As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result. the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they; propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes.

  • 22.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Becerra, Marley
    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.
    On the NOx generation in corona, streamer and low pressure electrical discharges2008In: The Open Atmospheric Science Journal, ISSN 1874-2823, E-ISSN 1874-2823, Vol. 2, p. 176-180Article in journal (Refereed)
  • 23.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Becerra, Marley
    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.
    On the NOx production in ‘cold’ electrical discharges2007In: International Conference on Atmospheric Electricity, ICAE, Beijing, China, 2007Conference paper (Other academic)
  • 24.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, C.
    Karolinska institutet.
    Andrews, C.J.
    Lightning caused injuries in humans2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 386-394Article in journal (Refereed)
    Abstract [en]

    A lightning flash may interact with humans in several ways. The possible pathways of interactions are direct strike, side flash, touch voltage, step voltage, subsequent stroke, connecting leaders and shock waves. The permanent or the temporary injuries that a victim suffers depend, among other parameters, on the type of interaction through which the body is exposed to a lightning strike and the path and the strength of the electric current passing through the body. In addition to the effects of electric current passing through the body, strong light and shock waves may also interact with the body in various ways. In this paper, the different types of injuries that may result from a lightning strike are documented and they are summarized, from engineering rather than a medical perspective

  • 25.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Dwyer, J.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rassoul, H.
    On the possibility of accelerating electrons to X-ray energies in the electric fields created during the meeting of positive and negative streamer fronts in laboratory electrical discharges2007Conference paper (Other academic)
  • 26.
    Cooray, Vernon
    et al.
    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.
    Rakov, Vladimir
    A model to represent negative and positive lightning first strokes with connecting leaders2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, no 2-4, p. 97-109Article in journal (Refereed)
    Abstract [en]

    A channel base current model of the current generation (CG) type is introduced to describe both negative and positive first return strokes. The key feature of the model is the association of the slow front of the channel base current waveform with the upward connecting leader. This feature is mathematically represented by a discharge propagation speed profile, which is characterized by an initial exponential increase with increasing height. It is shown that the previous models of the CG type may be incapable of reproducing adequately the observed electromagnetic fields when the channel base current contains a slow front.

  • 27.
    Cooray, Vernon
    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.
    Efficiencies for production of NOx and O3 by streamer discharges in air at atmospheric pressure2005In: 10th International Conference on Electrostatics, Helsinki, Finland, June 15-17, 2005Conference paper (Refereed)
  • 28.
    Cooray, Vernon
    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.
    Efficiencies for production of NOx and O3 by streamer discharges in air at atmospheric pressure2005In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 63, p. 977-983Article in journal (Refereed)
  • 29.
    Cooray, Vernon
    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.
    On the Mechanism of X-ray Generation in Dart Leaders of Lightning Flashes2008In: EOS Trans. AGU, 89(53), Fall Meet. Suupl., Abstract AE21A-05, San Francisco, USA, 2008Conference paper (Refereed)
  • 30.
    Cooray, Vernon
    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.
    On the relationship between the discharge current, energy dissipation and the NOx production in spark discharges2005In: International Conference on Lightning and static Electricity, ICOLSE, Seattle, Washington, USA, September 19-23, 2005, p. PHE-44.1-Conference paper (Refereed)
  • 31.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    Department of Electrical and Computer Engineering, University of Florida.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The lightning striking distance—Revisited2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 296-306Article in journal (Refereed)
    Abstract [en]

    First return stroke current waveforms measured by Berger [Methods and results of lightning records at Monte San Salvatore from 1963–1971 (in German), Bull. Schweiz. Elektrotech. ver. 63 (1972) 21403—21422] and Berger and Vogelsanger [Measurement and results of lightning records at Monte San Salvatore from 1955–1963 (in German), Bull. Schweiz. Elektrotech. ver. 56 (1965) 2–22] are used to estimate the charge stored in the lightning stepped leader channel. As opposed to previous charge estimates based on the entire current waveform, only the initial portion of measured current waveforms (100 μs in duration) was used in order to avoid the inclusion of any charges not involved in the effective neutralization of charges originally stored on the leader channel. The charge brought to ground by the return stroke within the first 100 μs, Qf,100 μs (in C) is related to the first return stroke peak current, Ipf (in kA), as Qf,100 μs=0.61 Ipf. From this equation the charge distribution of the stepped leader as a function of the corresponding peak return stroke current is estimated. This distribution (along with the assumed average electric field of 500 kV/m in the final gap) is used to estimate the lightning striking distance S (in meters) to a flat ground as a function of the prospective return stroke peak current I (in kA): S=1.9 Ipf0.90. For the median first stroke peak current of 30 kA one obtains S=41 m, while the traditional equation, S=10 Ipf0.65, gives S=91 m. In our view, the new equation for striking distance provides a more physically realistic basis for the electro-geometric approach widely used in estimating lightning incidence to power lines and other structures.

  • 32.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Rakov, Vladimir
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    The relationship between the leader charge and the return stroke current: Berger's data revisited2004In: International Conference on Lightning Protection, 2004Conference paper (Refereed)
  • 33.
    Cooray, Vernon
    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.
    The striking distance of lightning flashes and the early streamer emission (ESE) hypothesis2007In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, no 5-6, p. 336-341Article in journal (Refereed)
    Abstract [en]

    The attachment of a lightning flash to a lightning conductor (or to any other structure) takes place through a connecting leader that rises from the structure towards the descending stepped leader of a lightning flash. The spatial separation between the tip of the stepped leader and the lightning conductor (or the grounded structure) at the initiation of the connecting leader is known as the striking distance. In this paper the striking distance of stepped leaders is derived as a function of conductor height, conductor radii and the prospective return stroke current. Based on these results the validity of the early streamer emission (ESE) hypothesis is discussed. According to the ESE hypothesis, the striking distance of a lightning conductor can be increased by the artificial initiation of streamers from a lightning conductor. The results cast doubt on the validity of the ESE hypothesis. This in turn calls for more experimental data and field validations before using the ESE hypothesis in standard lightning protection practice.

  • 34.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Zitnik, Mihael
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Manyahi, Mighanda
    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.
    Rahman, Mahbubur
    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.
    Physical model of surge-current characteristics of buried vertical rods in the presence of soil ionisation2004In: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 60, p. 193-202Article in journal (Refereed)
  • 35.
    Danielsson, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Wave Energy Conversion: Linear Synchronous Permanent Magnet Generator2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis studies the electric aspects of a linear synchronous permanent magnet generator. The generator is designed for use in a wave energy converter, which determines the fundamental requirements of the generator. The electromagnetic properties of the generator are investigated with a finite element based simulation tool. These simulations formed the base of the design and construction of a laboratory prototype. Several experiments where conducted on the prototype generator. The results verify at large the simulation tool. However, a difference between the measured and simulated air gap flux was discovered. This was attributed to the longitudinal ends of the generator, which are ignored in the simulation tool. Experiences from the construction, and further finite element studies, led to a significant change in the support structure of the first offshore prototype generator. A complete wave energy converter was constructed and launched, the 13th of March, on the west coast of Sweden. A study of the load resistance impact on the power absorption has been carried out. An optimal load interval, with regard to power absorption, has been identified. Furthermore, the generator has proofed to withstand short term overload several times larger than the nominal load. Finally, the longitudinal ends’ influence on the flux distribution was investigated with an analytical model, as well as finite element simulations. A possible problem with large induction of eddy currents in the actuator back steel was identified.

    This work is a part of a larger project, which aims do develop a viable wave energy conversion system.

    List of papers
    1. Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator
    Open this publication in new window or tab >>Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator
    2006 (English)In: IEEE Transactions on Magnetics, Vol. 41, no 9, p. 2490-2495Article in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-94984 (URN)
    Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2018-05-31Bibliographically approved
    2. Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters
    Open this publication in new window or tab >>Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters
    2006 (English)In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 14, p. 1130-1145Article in journal (Refereed) Published
    Abstract [en]

    A directly coupled linear permanent magnet generator of longitudinal flux-type is investigated. The generator will be used for power take-off in a wave energy converter. A combined field- and circuit model, solved by a time stepping finite element technique, is used to model and analyse the electromagnetic behaviour of the machine. A large number of simulations form the basis of a design study where the influence of armature current level, number of cables per slot, and pole width is investigated with respect to efficiency, generator size, and the load angle. A case study is performed for a chosen generator design. The electromagnetic behaviour is examined both for nominal load and for overloads. The generator has a nominal output power of 10 kW for a constant piston speed of 0.7 m s(-1). The electromagnetic efficiency at nominal load is 86.0%, the load angle 6.6 degrees, and the power fluctuation 1.3%. At 300% overload the load angle barely exceeds 12 degrees and the cable temperature is below 25 degrees C provided that the stator back is thermally connected to the sea water. The numerical calculations have been verified for small speeds by experiments.

    Keyword
    design methodology, finite element, linear synchronous generators, permanent magnet, wave energy converter
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-95676 (URN)10.1002/er.1209 (DOI)000242188900002 ()
    Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
    3. Verification of Cyclic Boundary Condition and 2D Field Model for Synchronous PM Linear Generator
    Open this publication in new window or tab >>Verification of Cyclic Boundary Condition and 2D Field Model for Synchronous PM Linear Generator
    In: IEEE Transaction on MagneticsArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-94986 (URN)
    Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
    4. First experimental results from sea trials of a novel wave energy system
    Open this publication in new window or tab >>First experimental results from sea trials of a novel wave energy system
    Show others...
    In: Applied Physics LetterArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-94987 (URN)
    Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
    5. Analytic model of flux distribution in linear PM synchronous machines including longitudinal end effects
    Open this publication in new window or tab >>Analytic model of flux distribution in linear PM synchronous machines including longitudinal end effects
    In: Submitted to IEEE Transaction on MagneticsArticle in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-94988 (URN)
    Available from: 2006-10-20 Created: 2006-10-20Bibliographically approved
    6. Electromagnetic forces in the air gap of a permanent magnet linear generator at no load
    Open this publication in new window or tab >>Electromagnetic forces in the air gap of a permanent magnet linear generator at no load
    2006 (English)In: Journal of Applied Physics, Vol. 99, no 3, p. 1-5Article in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-94989 (URN)
    Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2016-06-22Bibliographically approved
    7. Measuring air gap width of permanent magnet linear generators using search coil sensor
    Open this publication in new window or tab >>Measuring air gap width of permanent magnet linear generators using search coil sensor
    2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 2, p. 024518-Article in journal (Refereed) Published
    Abstract [en]

    A concept for a wave power plant is being developed at the Centre for Renewable Electric Energy Conversion at the A˚ngström Laboratory at Uppsala University. The concept is based on a permanent magnet linear generator placed on the seabed, directly driven by a surface following buoy. Critical for the survival of the generator is that the air gap between the moving and static parts of the generator is constantly fixed at the designed width to prevent the moving and static parts from connecting during operation. This paper shows the design and evaluation of an inductive sensor for measuring the air gap width during generator operation. In order to survive during years on the seafloor inside the wave power plants, the sensor has deliberately been chosen to be a passive component, as well as robust and compact. A coil etched on a printed circuit board, i.e., a search coil, was the chosen basis for the sensor. The sensor has been tested on an existing test rig of a wave power plant and the results have been compared with finite element simulations.The results show that a search coil magnetic sensor etched on a printed circuit board is a suitable concept for measuring the air gap width. Experimentally measured and theoretically calculated sensor signals show very good agreement. The setup has a sensitivity of +/-0.4 mm in the range of 4-9.5 mm air gap. The potential for future improvements of the sensitivity is considerable.

    Keyword
    High-current and high-voltage technology: power systems; power transmission lines and cables, Electric motors, Spatial dimensions, Sensors ; remote sensing, Finite-element and Galerkin methods
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-94990 (URN)10.1063/1.2403964 (DOI)000243890800148 ()
    Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2017-12-14Bibliographically approved
    8. An electrical approach to wave energy conversion
    Open this publication in new window or tab >>An electrical approach to wave energy conversion
    Show others...
    2006 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, no 31, p. 1309-1319Article in journal (Refereed) Published
    Abstract [en]

    Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-95677 (URN)10.1016/j.renene.2005.07.009 (DOI)
    Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2017-12-14Bibliographically approved
    9. Simulated Response of a Linear Generator Wave Energy Converter
    Open this publication in new window or tab >>Simulated Response of a Linear Generator Wave Energy Converter
    2004 (English)In: Proceedings of the Fourteenth International Offshore and Polar Engineering Conference, 2004, p. 260-260Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-94992 (URN)1-880633-62-1 (ISBN)1098-6189 (ISBN)
    Conference
    ISOPE, 23-28 May, 2004, Toulon, France
    Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2013-07-31Bibliographically approved
    10. A direct drive wave energy converter: Simulations and experiments
    Open this publication in new window or tab >>A direct drive wave energy converter: Simulations and experiments
    Show others...
    2005 (English)In: Proc of 24th International Conference on Offshore Mechanics & Arctic Engineering, American Society of Mechanical Engineers , 2005Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    American Society of Mechanical Engineers, 2005
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-94993 (URN)
    Conference
    24th International Conference on Mechanics and Arctic Engineering (OMAE), Halkidiki, Greece, June 12-17
    Available from: 2006-10-20 Created: 2006-10-20 Last updated: 2013-07-31Bibliographically approved
  • 36.
    Danielsson, Oskar
    et al.
    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.
    Study of a Longitudinal Flux Permanent Magnet Linear Generator for Wave Energy Converters2006In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 14, p. 1130-1145Article in journal (Refereed)
    Abstract [en]

    A directly coupled linear permanent magnet generator of longitudinal flux-type is investigated. The generator will be used for power take-off in a wave energy converter. A combined field- and circuit model, solved by a time stepping finite element technique, is used to model and analyse the electromagnetic behaviour of the machine. A large number of simulations form the basis of a design study where the influence of armature current level, number of cables per slot, and pole width is investigated with respect to efficiency, generator size, and the load angle. A case study is performed for a chosen generator design. The electromagnetic behaviour is examined both for nominal load and for overloads. The generator has a nominal output power of 10 kW for a constant piston speed of 0.7 m s(-1). The electromagnetic efficiency at nominal load is 86.0%, the load angle 6.6 degrees, and the power fluctuation 1.3%. At 300% overload the load angle barely exceeds 12 degrees and the cable temperature is below 25 degrees C provided that the stator back is thermally connected to the sea water. The numerical calculations have been verified for small speeds by experiments.

  • 37.
    Danielsson, Oskar
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Leijon, Mats
    Analytic model of flux distribution in linear PM synchronous machines including longitudinal end effectsIn: Submitted to IEEE Transaction on MagneticsArticle in journal (Refereed)
  • 38.
    Danielsson, Oskar
    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, Electricity.
    Sjöstedt, Elisabeth
    Detailed Study of the Magnetic Circuit in a Longitudinal Flux Permanent-Magnet Synchronous Linear Generator2006In: IEEE Transactions on Magnetics, Vol. 41, no 9, p. 2490-2495Article in journal (Refereed)
  • 39.
    Danielsson, Oskar
    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.
    Thorburn, Karin
    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.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    A direct drive wave energy converter: Simulations and experiments2005In: Proc of 24th International Conference on Offshore Mechanics & Arctic Engineering, American Society of Mechanical Engineers , 2005Conference paper (Refereed)
  • 40.
    Danielsson, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabeth
    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.
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Simulated Response of a Linear Generator Wave Energy Converter2004In: Proceedings of the Fourteenth International Offshore and Polar Engineering Conference, 2004, p. 260-260Conference paper (Refereed)
  • 41.
    Danielsson, Oskar
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Stålberg, Magnus
    Verification of Cyclic Boundary Condition and 2D Field Model for Synchronous PM Linear GeneratorIn: IEEE Transaction on MagneticsArticle in journal (Refereed)
  • 42. Dwyer, J. R.
    et al.
    Saleh, Z.
    Rassoul, H. K.
    Concha, D.
    Rahman, Mahbubur
    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.
    Jerauld, J.
    Uman, M. A.
    Rakov, V. A.
    A study of X-ray emission from laboratory sparks in air at atmospheric pressure2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, p. D23207-Article in journal (Refereed)
  • 43.
    Eriksson, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Isberg, 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.
    Theory and Experiment on an Elastically Moored Cylindrical Buoy2006In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 31, no 4, p. 959-963Article in journal (Refereed)
    Abstract [en]

    In this paper, we compare simulated forces and accelerations for a moored floating buoy with full-scale experimental results in real ocean waves. The buoy is moored with a wire connected by springs to a concrete foundation situated at the seafloor. This study aims to develop a computer model using potential theory with a linearized free-surface boundary condition to describe the motion of such a system. The intention is to use the model for future study of wave-energy absorption and design of converters. Another objective is to see how complex a model is required to get accurate results. The method used is computationally fast and makes it possible to couple linear buoy wave interaction with nonlinear generator models, so that different loads and latching can be studied. A computationally fast method is required to model farms of wave-energy converters.

  • 44.
    Eriksson, Mikael
    et al.
    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.
    Dynamics of a Linear Generator for Wave Energy Conversion2004Conference paper (Refereed)
  • 45. Fernandoa, Mahendra
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on the electric field time derivatives generated by return strokes in lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1388-1396Article in journal (Refereed)
    Abstract [en]

    The effects of propagation over finitely conducting ground on the features of radiation component of the electric field time derivatives are investigated. The results show that the peak, the half-width and the risetime of the electric field time derivative change significantly in propagating over finitely conducting ground. Furthermore, any correlation that may exist between various parameters could also change significantly due to propagation effects. Consequently, in return stroke model validations using experimentally measured fields, remote sensing of return stroke current time derivatives using measured electric field time derivatives and in the calculation of induced voltages generated by lightning flashes in electrical installations the distortions caused by propagation effects on the electric field time derivatives cannot be neglected.

  • 46.
    Hagnestål, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Moiseenko, Vladimir
    Coil design for the straight field line mirror2009In: Fusion science and technology, ISSN 1536-1055, E-ISSN 1943-7641, Vol. 55, no 2T, p. 127-130Article in journal (Refereed)
    Abstract [en]

    Coil systems for producing the Straight Field Line Mirror field using axisymmetric and quadrupolar coils are calculated. Two applications are intended, a fusion-fission nuclear waste transmutation device and a small plasma deposition device. Position, size and current for the axisymmetric coils are optimized as well as radial profile and current for the quadrupolar coils for the two applications. Calculations show that such a coil system can produce the Straight Field Line Mirror field for long-thin mirrors with moderate mirror ratio, but some other coil configuration needs to be found for mirrors where the coils cannot reside close to the plasma edge. In this work, the material science experiment mirror can be produced with about 1% error but the fusion-fission device field has not at this moment been reproduced with acceptable errors.

  • 47. Henfridsson, Urban
    et al.
    Neimane, Viktoria
    Strand, Kerstin
    Kapper, Robert
    Bernhoff, Hans
    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.
    Sundberg, Jan
    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.
    Ericsson, Ellerth
    Bergman, Karl
    Wave energy potential in the Baltic Sea and the Danish part of the North Sea, with reflections on the Skagerrak2007In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 32, no 12, p. 2069-2084Article in journal (Refereed)
    Abstract [en]

    Wave power, along with renewable energy-generating sources like tides and streams, is underestimated considering its advantageous physical properties and predictability. This paper examines possible examples of wave power installations in the Baltic Sea and the Danish part of the North Sea. Hindcasting data is used allowing estimations of wave energy generated and results show promising areas in the North Sea, but also several parts of the Baltic Sea are of interest. The study is based upon linear generator technique, placed on the seabed using point-absorbers arranged in arrays of up to several thousand units. The study aims at showing the physical possibilities of wave energy, including economical feasibility and environmental advantages of wave energy even in moderate wave climates. With discussion from two examples in the Baltic Sea, one in the Danish North Sea and a new pilot study site in the Swedish part of Skagerrak, this study show feasible illustrations of wave energy takeouts. Project examples vary in size due to distance to grid, grid voltage, and may thus be economically feasible. Examples also show considerations in societal and nature conservation matters, including aspects such as industrial and military interests, archaeological or marine reserves and local geology. The authors conclude that wave energy electric conversion is an option that needs more attention and which has several advantages compared to conventional renewable sources. Sound engineering, in combination with producer, consumer and broad societal perspective is advised for a sustainable development of wave energy conversion.

  • 48.
    Lehto, Marcus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Bodén, Roger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Simu, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Micro Structural Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Schweitz, Jan-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    A polymeric paraffin microactuator2008In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 17, no 5, p. 1172-1177Article in journal (Refereed)
    Abstract [en]

    Paraffin wax is a promising material in microactuators not only because of its ability of producing large displacements and high forces at the same time but also because of the variety of manufacturing techniques available. In this paper, a simple actuator based on paraffin wax as the active material is fabricated and tested. Ultraviolet-curable epoxy is used in a technique combining simultaneous moulding and liquid-phase photopolymerization in a single-process step to build the stiff part of the actuator body. A heater is integrated in the paraffin reservoir, and a polyimide tape is used as the deflecting membrane. Thermornechanical analysis of the paraffin wax shows that it exhibits a volume expansion of 10%, including phase transitions and linear expansion. As for the actuator, a stroke of 90 mu m is obtained for the unloaded device, whereas 37 mu m is recorded with a 0.5-N contact load at a driving voltage of 0.71 V and a frequency of 1/32 Hz. The actuator can be used in microsystems, where both large strokes and forces are needed. The low-cost materials and low driving voltage also makes it suitable for disposable systems.

  • 49.
    Leijon, Mats
    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.
    Segergren, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences.
    Assembly comprising a Water Turbine and a Generator, the Rotor of which is Direct-Connected to each one of the Blades the Turbine: PCT-application for Swedish patent SE 0400667-22005Patent (Other (popular science, discussion, etc.))
  • 50.
    Leijon, Mats
    et al.
    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.
    Eriksson, Mikael
    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.
    Isberg, Jan
    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.
    Ivanova, Irina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Sjöstedt, Elisabet
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Ågren, Olov
    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.
    An electrical approach to wave energy conversion2006In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, no 31, p. 1309-1319Article in journal (Refereed)
    Abstract [en]

    Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project.

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