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  • 201.
    Bayazit, Dervis
    et al.
    Federal Home Loan Bank of Atlanta, Financial Risk Modeling Department, Atlanta GA.
    Uzunoglu, Bahri
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Simplex optimization for particle filter joint parameter estimation of electricity prices with jump diffusion2013Inngår i: Journal of financial and economic practice, Vol. 13, nr 2, s. 1-14Artikkel i tidsskrift (Fagfellevurdert)
  • 202.
    Becerra, Marley
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    On the Attachment of Lightning Flashes to Grounded Structures2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis deals with the physical modeling of the initiation and propagation of upward positive leader discharges from grounded structures during lightning strikes. It includes the analysis of upward leaders initiated under the influence of the electric field produced by a dominant negative cloud charge and due to the combined action of a negative thundercloud and a descending downward stepped negative leader. Thus, a self-consistent model based on the physics of leader discharges is developed for the evaluation of the attachment of lightning flashes to any kind of grounded structure. The predictions of the model have been found to be in good agreement with the results of laboratory long air gap experiments and with classical and altitude rocket triggered lightning experiments.

    Due to the high application level and predictive power of the developed model, several contributions to the physical understanding of factors influencing the initiation and propagation of upward positive leaders during thunderstorms have been made. For instance, it has been found that the initiation of upward connecting leaders is strongly affected by the average velocity of the downward stepped leader. Similarly, it is shown that the switching voltage impulses used in the laboratory do not “fairly approximate” the electric fields produced by a descending downward leader, as claimed by supporters of Early Streamer Emission (ESE) devices. Furthermore, it is found that the space charge layer created by corona at ground level significantly increases the thundercloud electric fields required to initiate upward lightning leaders from tall objects. On the other hand, it is also shown that the upward leader velocity depends on the downward leader average velocity, the prospective return stroke current, the lateral distance of the downward leader channel and the ambient electric field.

    By implementing the model to the analysis of complex structures, it has been observed that the corners of actual buildings struck by lightning coincide rather well with the places characterized by low leader inception electric fields. Besides, it has been found that the leader inception zones of the corners of complex structures do not define symmetrical and circular regions as it is generally assumed.

    Delarbeid
    1. A simplified physical model to determine the lightning upward connecting leader inception
    Åpne denne publikasjonen i ny fane eller vindu >>A simplified physical model to determine the lightning upward connecting leader inception
    2006 (engelsk)Inngår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, Vol. 21, nr 2, s. 897-908Artikkel i tidsskrift (Fagfellevurdert) Published
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97281 (URN)
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2016-06-22bibliografisk kontrollert
    2. Time dependent evaluation of the lightning upward connecting leader inception
    Åpne denne publikasjonen i ny fane eller vindu >>Time dependent evaluation of the lightning upward connecting leader inception
    2006 (engelsk)Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, nr 21, s. 4695-4702Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97282 (URN)10.1088/0022-3727/39/21/029 (DOI)000242476000031 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    3. Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals
    Åpne denne publikasjonen i ny fane eller vindu >>Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals
    2008 (engelsk)Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, nr 8, s. 085204-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The early emission of streamers in laboratory long air gaps under switching impulses has been observed to reduce the time of initiation of leader positive discharges. This fact has been arbitrarily extrapolated by the manufacturers of early streamer emission devices to the case of upward connecting leaders initiated under natural lightning conditions, in support of those non-conventional terminals that claim to perform better than Franklin lightning rods. In order to discuss the physical basis and validity of these claims, a self-consistent model based on the physics of leader discharges is used to simulate the performance of lightning rods in the laboratory and under natural lightning conditions. It is theoretically shown that the initiation of early streamers can indeed lead to the early initiation of self-propagating positive leaders in laboratory long air gaps under switching voltages. However, this is not the case for positive connecting leaders initiated from the same lightning rod under the influence of the electric field produced by a downward moving stepped leader. The time evolution of the development of positive leaders under natural conditions is different from the case in the laboratory, where the leader inception condition is closely dependent upon the initiation of the first streamer burst. Our study shows that the claimed similarity between the performance of lightning rods under switching electric fields applied in the laboratory and under the electric field produced by a descending stepped leader is not justified. Thus, the use of existing laboratory results to validate the performance of the early streamer lightning rods under natural conditions is not justified.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97283 (URN)10.1088/0022-3727/41/8/085204 (DOI)000254329500024 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    4. Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers
    Åpne denne publikasjonen i ny fane eller vindu >>Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers
    2007 (engelsk)Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, nr D12, s. D12205-Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    Emneord
    North America, United States, Florida, density currents, Current density, concentration, particles, aerosols, Charge density, experimental studies, time variations, Thunderstorm, digital simulation, numerical models, Thundercloud, shields, electrical field, lightning, Space charge
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97284 (URN)10.1029/2006JD008308 (DOI)000247534000003 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    5. A self-consistent upward leader propagation model
    Åpne denne publikasjonen i ny fane eller vindu >>A self-consistent upward leader propagation model
    2006 (engelsk)Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 39, nr 16, s. 3708-3715Artikkel i tidsskrift (Fagfellevurdert) Published
    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.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97285 (URN)10.1088/0022-3727/39/16/028 (DOI)000239613700040 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    6. On the velocity of positive connecting leaders associated with negative downward lightning leaders
    Åpne denne publikasjonen i ny fane eller vindu >>On the velocity of positive connecting leaders associated with negative downward lightning leaders
    2008 (engelsk)Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, s. L02801-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A self-consistent leader propagation model is used to estimate the velocity of upward connecting positive leaders initiated from a tall tower under the influence of downward negative lightning leaders. The propagation of upward connecting leaders has been found to be influenced not only by the average velocity of the downward leader but also by the prospective return stroke current, the lateral position of the downward leader channel as well as by the ambient electric field. This result show that the velocity and propagation time of upward connecting positive leaders change from flash to flash due to the variations in these parameters.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97286 (URN)10.1029/2007GL032506 (DOI)000252566900008 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    7. Identification of lightning vulnerability points on complex grounded structures
    Åpne denne publikasjonen i ny fane eller vindu >>Identification of lightning vulnerability points on complex grounded structures
    2007 (engelsk)Inngår i: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, nr 9, s. 562-570Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The identification of the most vulnerable points on a given structure to be struck by lightning is an important issue on the design of a reliable lightning protection system. Traditionally, these lightning strike points are identified using the rolling sphere method, through an empirical correlation with the prospective peak return stroke current. However, field observations in Kuala Lumpur and Singapore have shown that the points where lightning flashes strike buildings also depend on the height and geometry of the structure. Since a lightning strike point is believed to be the place on a grounded structure where a propagating upward leader is first initiated, a physical leader inception model is used here to estimate the background electric field required to initiate a stable upward leader from the corners of some complex buildings. The computed location of the points from where leaders are incepted are compared with the damaged points on buildings struck by lightning. The observed lightning strike points coincide rather well with the corners of the buildings which are characterized by lower leader inception electric fields. Furthermore, it is found that the geometry of the buildings significantly influences the conditions necessary to initiate upward leaders and, therefore, the location of the most likely strike points.

    Emneord
    Lightning, Lightning protection, Lightning strike points, Air terminals, External lighting protection systems
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97287 (URN)10.1016/j.elstat.2006.12.003 (DOI)000248704500003 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2017-12-14bibliografisk kontrollert
    8. Lightning striking distance of complex structures
    Åpne denne publikasjonen i ny fane eller vindu >>Lightning striking distance of complex structures
    2008 (engelsk)Inngår i: IET Generation, Transmission and Distribution, ISSN 1751-8687, Vol. 2, nr 1, s. 131-138Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Traditionally, the location of lightning strike points has been determined by using the rolling sphere method, but recently the collection volume method (CVM) has also been proposed for the placement of air terminals on complex structures. Both these methods are empirical in nature and a more advanced model based on physics of discharges is needed to improve the state of affairs. This model is used to evaluate the striking distance from corners and air terminals on actual buildings and the results are qualitatively compared with the predictions of the rolling sphere method and the CVM. The results show that the striking distance not only depends upon the prospective return stroke current and the geometry of the building, but also on the lateral position of the downward leader with respect to the strike point. A further analysis is performed to qualitatively compare the lightning attraction zones obtained with the CVM and the leader inception zones obtained for a building with and without air terminals. The obtained results suggest that the collection volume concept overestimates the protection areas of air terminals placed on complex structures, bringing serious doubts on the validity of this method.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-97288 (URN)10.1049/iet-gtd:20070099 (DOI)000252958100015 ()
    Tilgjengelig fra: 2008-05-14 Laget: 2008-05-14 Sist oppdatert: 2016-04-12bibliografisk kontrollert
    Fulltekst (pdf)
    FULLTEXT01
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    COVER01
  • 203.
    Becerra, Marley
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    On The Initiation of Upward Positive Leader Discharges During Lightning Strikes2007Licentiatavhandling, monografi (Annet vitenskapelig)
  • 204.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    A simplified model to represent the inception of upward leaders from grounded structures under the influence of lightning stepped leaders2005Inngår i: VIII International Symposium on Lightning Protection, SIPDA, Sao Paulo, Brazil, November 21-25, 2005Konferansepaper (Fagfellevurdert)
  • 205.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    A Simplified Physical Model to Determine the Lightning Upward Connecting Leader Inception2006Inngår i: IEEE Transactions on Power Delivery, Vol. 21, nr 2, s. 897-908Artikkel i tidsskrift (Fagfellevurdert)
  • 206.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    An improved upward leader propagation model2006Inngår i: Proceedings of the 28th Internat Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, s. 581-586Konferansepaper (Fagfellevurdert)
  • 207.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Dynamic modeling of the lightning upward connecting leader inception2006Inngår i: Proceedings of the 28th International Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, s. 543-548Konferansepaper (Fagfellevurdert)
  • 208.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Early streamer emission principle does not work under natural lightning!2008Konferansepaper (Fagfellevurdert)
  • 209.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Laboratory experiments cannot be utilized to justify the action of Early Streamer Emission terminals2008Inngår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, nr 8, s. 085204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The early emission of streamers in laboratory long air gaps under switching impulses has been observed to reduce the time of initiation of leader positive discharges. This fact has been arbitrarily extrapolated by the manufacturers of early streamer emission devices to the case of upward connecting leaders initiated under natural lightning conditions, in support of those non-conventional terminals that claim to perform better than Franklin lightning rods. In order to discuss the physical basis and validity of these claims, a self-consistent model based on the physics of leader discharges is used to simulate the performance of lightning rods in the laboratory and under natural lightning conditions. It is theoretically shown that the initiation of early streamers can indeed lead to the early initiation of self-propagating positive leaders in laboratory long air gaps under switching voltages. However, this is not the case for positive connecting leaders initiated from the same lightning rod under the influence of the electric field produced by a downward moving stepped leader. The time evolution of the development of positive leaders under natural conditions is different from the case in the laboratory, where the leader inception condition is closely dependent upon the initiation of the first streamer burst. Our study shows that the claimed similarity between the performance of lightning rods under switching electric fields applied in the laboratory and under the electric field produced by a descending stepped leader is not justified. Thus, the use of existing laboratory results to validate the performance of the early streamer lightning rods under natural conditions is not justified.

  • 210.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    On the interaction of lightning upward connecting positive leaders with humans2009Inngår i: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 51, nr 4, s. 1001-1008Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Upward connecting leaders can be initiated from humans under the influence of lightning downward stepped leaders, thereby causing severe injuries. In order to improve the scarce knowledge about the interaction of upward connecting leaders with humans, a self-consistent model based on the physics of leader discharges is used in this paper. Furthermore, a current-generation-type return-stroke model is applied to calculate the current pulse produced during the neutralization of unsuccessful aborted upward leaders. It is estimated that an upward connecting leader can be initiated even when the victim is located several tens of meters away from the lightning channel. However, the lightning exposure to a direct strike and to an aborted leader is found to be reduced by 50% and 70%, respectively, when an individual standing straight adopts the squat position. In the case of an aborted upward leader, it is estimated that a short-duration pulse of opposite polarity in the kiloampere range would be produced by the neutralization of the leader charge. Rough estimates of the total energy dissipated in the victim's body by the current of an aborted unsuccessful upward leader range between hundred and thousand joules.

  • 211.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    On the physics of the interaction of aborted lightning upward connecting leaders with humans2008Konferansepaper (Fagfellevurdert)
  • 212.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    On the velocity of positive connecting leaders associated with negative downward lightning leaders2008Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, s. L02801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A self-consistent leader propagation model is used to estimate the velocity of upward connecting positive leaders initiated from a tall tower under the influence of downward negative lightning leaders. The propagation of upward connecting leaders has been found to be influenced not only by the average velocity of the downward leader but also by the prospective return stroke current, the lateral position of the downward leader channel as well as by the ambient electric field. This result show that the velocity and propagation time of upward connecting positive leaders change from flash to flash due to the variations in these parameters.

  • 213.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Velocity of Laboratory Electrical Discharges at low Pressure2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Abstract AE42A-05

  • 214.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Abidin, Hartono Zainal
    Location of the vulnerable points to be struck by lightning in complex structures2005Inngår i: International Conference on Lightning and Static Electricity, Seattle, 2005, s. GND-20.1Konferansepaper (Fagfellevurdert)
  • 215.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Acácio, Silva Neto
    Piantini, Alexandre
    Lightning attachment to power transmission lines: on the validity of the electrogeometric model2008Konferansepaper (Fagfellevurdert)
  • 216.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Hartono, Zainal
    Identification of lightning vulnerability points on complex grounded structures2007Inngår i: Journal of Electrostatics, ISSN 0304-3886, E-ISSN 1873-5738, Vol. 65, nr 9, s. 562-570Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The identification of the most vulnerable points on a given structure to be struck by lightning is an important issue on the design of a reliable lightning protection system. Traditionally, these lightning strike points are identified using the rolling sphere method, through an empirical correlation with the prospective peak return stroke current. However, field observations in Kuala Lumpur and Singapore have shown that the points where lightning flashes strike buildings also depend on the height and geometry of the structure. Since a lightning strike point is believed to be the place on a grounded structure where a propagating upward leader is first initiated, a physical leader inception model is used here to estimate the background electric field required to initiate a stable upward leader from the corners of some complex buildings. The computed location of the points from where leaders are incepted are compared with the damaged points on buildings struck by lightning. The observed lightning strike points coincide rather well with the corners of the buildings which are characterized by lower leader inception electric fields. Furthermore, it is found that the geometry of the buildings significantly influences the conditions necessary to initiate upward leaders and, therefore, the location of the most likely strike points.

  • 217.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Roman, F
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. elektricitetslära och åskforskning.
    Striking distance of vulnerable points to be struck by lightning on complex structures2006Inngår i: Proceedings of the 28th International Conference on Lightning Protection, ICLP, Kanazawa, Japan, 2006, s. 608-613Konferansepaper (Fagfellevurdert)
  • 218.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Roman, Francisco
    Lightning striking distance of complex structures2008Inngår i: IET Generation, Transmission and Distribution, ISSN 1751-8687, Vol. 2, nr 1, s. 131-138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditionally, the location of lightning strike points has been determined by using the rolling sphere method, but recently the collection volume method (CVM) has also been proposed for the placement of air terminals on complex structures. Both these methods are empirical in nature and a more advanced model based on physics of discharges is needed to improve the state of affairs. This model is used to evaluate the striking distance from corners and air terminals on actual buildings and the results are qualitatively compared with the predictions of the rolling sphere method and the CVM. The results show that the striking distance not only depends upon the prospective return stroke current and the geometry of the building, but also on the lateral position of the downward leader with respect to the strike point. A further analysis is performed to qualitatively compare the lightning attraction zones obtained with the CVM and the leader inception zones obtained for a building with and without air terminals. The obtained results suggest that the collection volume concept overestimates the protection areas of air terminals placed on complex structures, bringing serious doubts on the validity of this method.

  • 219.
    Becerra, Marley
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Francisco, Roman
    Cooray, Vernon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Lightning attachment to common structures: is the rolling sphere method really adequate?2008Konferansepaper (Fagfellevurdert)
  • 220.
    Behnood, Aref
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Optimal Operation of Battery Energy Storage Systems in Radial Distribution Networks2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In recent years, power systems are facing with various challenges arising from the increased share of renewable energy systems. Among all sections of power systems, distribution grids are affected the most since the majority of renewable energy sources are connected to distribution grids.

    As the penetration of Variable Energy Sources increases in electric grids, energy storage systems have become more influential. In this context, this thesis presents a new algorithm for the optimal operation of Battery Energy Storage Systems in distribution grids. The proposed algorithm aims to define the optimal operation of Battery Energy Storage Systems considering the network topology, the output power of Variable Energy Sources and the electricity prices from the one-day ahead electric market as well as real time control of the batteries through smart appliances.

    In order to do this, firstly a comprehensive study on the existing Optimal Power Flow methods is carried out. Then, AR-OPF which is a novel Optimal Power Flow method for radial distribution systems is presented and the required mathematical constraints, equations and parameters of Battery Energy Storage Systems for modelling in distribution systems are described. Then, the problem formulation and the proposed algorithm are discussed in detail.

    Further to energy storage as the main function of Battery Energy Storage Systems, the impact of the proposed method on other functions of Battery Energy Storage Systems such as voltage control, grid support and loss reduction will be investigated. In order to do so, the proposed algorithm is applied to the IEEE 34 node test system as a case study. This will be carried out through defining several different scenarios. Finally, a sensitivity analysis is performed on the size of the existing batteries and the electricity price. The thesis will be concluded by the findings and possible future works.

    Fulltekst (pdf)
    fulltext
  • 221.
    Bender, Anke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Francisco, Francisco G. A.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sundberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    A Review of Methods and Models for Environmental Monitoring of Marine Renewable Energy2017Inngår i: Proceedings of the 12th European Wave and Tidal Energy Conference, EWTEC , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A continued expansion of the marine renewable energy sector will result in an increased demand in monitoring the natural marine environment. This may be due to a basic scientific interest but is foremost linked to the requirement of pre- and post-construction studies in relation to environmental impact assessments and consenting processes for marine renewable energy projects. With focus on wave and tidal power, but without attempting to provide a comprehensive list, we review methods, technologies and other scientific tools used for monitoring and predicting possible impacts from marine energy installations, on both population and behavioural levels. This includes traditional methods such as fishing gear, like nets and cages, modern technologies such as platforms with multi parameter equipment and the use of deterministic models. This paper is intended to serve as an overview for technology developers as well as authorities, regulators and decision makers with interests in general techniques, and naturally for scientists and consultants commonly being executors of studies and monitoring programs. By giving relevant and up to date references this paper may also be useful for finding more detailed information on study methods and variants. Finally, we give recommendations on where development of technologies is needed in order to face future requirements.

    Fulltekst (pdf)
    fulltext
  • 222.
    Bender, Anke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sundberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Effects from wave power generators on the distribution of two sea pen species on the Swedish west coast2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Global electricity demand doubled between 1990 and 2016 and several countries are planning for a significant increase in offshore renewable energies along the European coast. In 2015 renewable energy accounted for more than half of the new generating capacity installed in the power sector worldwide. These activities bring up an increased interest about possible environmental impacts or additional values of the new technologies. The Wave Energy Park "Sotenäs Project" is located on the west coast of Sweden, 120 km north of Gothenburg, and was the site for environmental impact studies from wave energy generators on two sea pen species, Virgularia mirabilis (Müller, 1776) and Pennatula phosphorea (Linnaeus, 1758). Sea pens and burrowing mega fauna communities are designated threatened or declining habitats or species by the OSPAR convention. Investigations of those taxa in relation to marine renewable energies are thereby both interesting and important. A ROV aided seabed survey in the wave power park and respective control areas were primarily conducted to assess Nephrops norvegicus (Linnaeus, 1758) abundance and video footages were used to compare the abundance of the two sea pen species within the same area. Preliminary results show a significant difference between the transects and years. However, a clear increased number of individuals inside the wave power park for the two sea pen species compared to the control transects were not identified. Long-term observations and complementary studies are necessary in order to draw firm conclusions.

  • 223.
    Bender, Anke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sundberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Effects of Wave Energy Generators on Nephrops norvegicus2018Inngår i: AWTEC 2018 Proceedings, 2018, artikkel-id 283Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Wave energy research is primarily focused on the technical developments of energy conversion but the parallel evaluation of environmental effects related to wave energy is also essential and reflects sustainable development of renewable energy. At the west coast of Sweden, 120 km north of Gothenburg, the Wave Energy Park “Sotenäs Project” is located. This area has been the location of environmental impact studies from wave energy generators on the macro crustacean species Nephrops norvegicus (Linnaeus, 1758), the Norway lobster. The Norway lobster is an ecologically as well as economically important species in Sweden and across Europe. The aim of this preliminary study was to detect possible positive or negative effects on numbers of individuals by the presence of the wave energy generators and the created “no take” zone. For that purpose, ROV aided seabed recordings of the characteristic Norway lobster burrow entrances were conducted inside the Wave Energy Park and respective control areas in 2016 and 2017. Preliminary results do not show a clear distinct result between the different transects and years. Long-term observations and complementary studies are necessary to draw conclusions and outweigh extreme and rare events of annual one-time samplings.

    Fulltekst (pdf)
    fulltext
  • 224.
    Bender, Anke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sundberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Environmental effects from wave power-Impacts on the Norway lobster2018Konferansepaper (Annet vitenskapelig)
  • 225.
    Bender, Anke
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Sundberg, Jan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Langhamer, Olivia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Chalmers Univeristy.
    Environmental effects from wave power devices on local fish and crustacean communities2018Konferansepaper (Annet vitenskapelig)
  • 226.
    Bengtsson, Sara
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Modelling of a Power System in a Combined Cycle Power Plant2011Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Simulators for power plants can be used for many different purposes, like training for operators or for adjusting control systems, where the main objective is to perform a realistic behaviour for different operating conditions of the power plant. Due to an increased amount of variable energy sources in the power system, the role of the operators has become more important. It can therefore be very valuable for the operators to try different operating conditions like island operation.

    The aim of this thesis is to model the power system of a general combined-cycle power plant simulator. The model should contain certain components and have a realistic behaviour but on the same time be simple enough to perform simulations in real time. The main requirements are to simulate cold start, normal operation, trip of generator, a controlled change-over to island operation and then resynchronisation.

    The modelling and simulations are executed in the modelling software Dymola, version 6.1. The interface for the simulator is built in the program LabView, but that is beyond the scope of this thesis.

    The results show a reasonable performance of the power system with most of the objectives fulfilled. The simulator is able to perform a start-up, normal load changes, trip of a generator, change-over to island operation as well as resynchronisation of the power plant to the external power grid. However, the results from the changing-over to island operation, as well as large load losses during island operation, show an unreasonable behaviour of the system regarding the voltage magnitude at that point. This is probably due to limitations in calculation capacity of Dymola, and the problem has been left to further improvements due to lack of time.

    There has also been a problem during the development of a variable speed regulated induction motor and it has not been possible to make it work due to lack of enough knowledge about how Dymola is performing the calculations. Also this problem has been left to further improvements due to lack of time.

    Fulltekst (pdf)
    FULLTEXT01
  • 227.
    Berg, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Linder, Maria
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Säkerhetsklassificering av dammar: En kartläggning av system i Sverige, Norge, Finland, Schweiz, Kanada och USA2013Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    In a comparing survey this thesis investigates

    classification systems for dams in Sweden, Norway,

    Finland, Switzerland, Canada and USA. The

    investigation is aiming at an understanding of how

    potential consequences of a dam failure are taken

    into account when classifying dams. Furthermore,

    the significance of the classification, regarding the

    requirements on the dam owner and surveillance

    authorities concerning dam safety is considered and

    reviewed. The thesis is pointing out similarities and

    differences in the line of dam safety.

    The survey of dam safety is firstly based upon legal

    requirements in the different countries and

    secondly on guidelines regarding dam safety. Dam

    owners generally are ultimately responsible for the

    safety of their dam, and often have their own

    routines regarding how this safety is to be achieved.

    In this thesis, however, the legal requirements are

    mainly focused upon.

    The investigation has resulted in an outlining of

    eight areas, where the classification systems in the

    various countries have been compared. The result

    has shown that although the consequence based

    classification systems of dams generally are based

    on similar parameters, the evaluation and

    determination of consequences due to dam failure

    differ, as do the system of responsibility regarding

    surveillance authorities.

    Fulltekst (pdf)
    fulltext
  • 228.
    Berggren, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Study of auxiliary power systemsfor offshore wind turbines: an extended analysis of a diesel gen-setsolution2013Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Until today the offshore wind power has grown in a steady pace and many new wind farms are being constructed around the globe. An important factor that is investigated today in the industry are the security of power supply to the equipment needed for controlling the offshore system during emergency situations. When a offshore wind farm is disconnected from the external grid and an emergency case occur the wind turbine generators lose their ability to transfer power and they are forced to be taken out of operation. As there are a number of loads in the wind turbines (navigation lights, sensor- and communication-apparatus, ventilation- and heating equipment etc.) they have a load demand which must be supplied in emergency mode. The German Transmission System operator (TSO) TenneT GmbH has set a requirement that the wind turbines is to be supplied by an auxiliary power supply (APS) in 12 hours and therefore there is need for a long-term auxiliary power supply system. This master thesis was assigned to investigate the most feasible APS-system. From the study of a number of different APS's one concept was chosen. This was the diesel gen-set solution placed on an offshore substation at sea. The system was modeled in the software DIgSILENT PowerFactory where a load flow analysis validated the calculated data and a study of the impact of  transients in the system was performed.

    Fulltekst (pdf)
    MasterThesis_JoakimBerggren_8803220451
  • 229.
    Bergkvist, Mikael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Roos, Arne
    Ribbing, Carl G
    Anomalies in integrating sphere measurements on structured samples1988Inngår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 27, nr 18Artikkel i tidsskrift (Fagfellevurdert)
  • 230.
    Berglund, Albin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Evolution of Cavity Tip Vortices in High-Pressure Turbines2017Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    This degree project in applied physics studies the tip gap flows over the rotor blades of a high-pressure turbine. The rotor blade used in the study has an improved design that utilizes both a cavity tip and an uneven profiling to reduce turbine loss. The designed rotor blade is shown to admit a 21% lower leakage mass flow rate across the tip gap than a reference rotor blade with a flat tip. By studying the designed rotor blade using transient CFD, the flow field of the tip gap region has been studied through one blade passage. The flow field characteristics of particular interest are the leakage mass flow rate across the tip gap region, which is proportional to turbine loss, and the characteristic vortices that reside within the cavity tip. By using post-processing scripts, the leakage mass flow rate has been calculated for every time step across one blade passage, showing a strong time dependence. The characteristic vortices are found using two different vortex detection algorithms, and their respective vorticity magnitude is shown to depend on the leakage mass flow rate. The simulation shows that the vorticity magnitude is increasing above a threshold of leakage mass flow rate, and that it is decreasing under this threshold. This effect is shown to destabilize the leakage mass flow rate, increasing its amplitude over its period of one blade passage.

    Fulltekst (pdf)
    Evolution of Cavity Tip Vortices in High-Pressure Turbines
  • 231.
    Bergman, Adam
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Utvärdering av Blitzortung blixtlokaliseringssystem: En jämförande studie med SMHI som referenssystem2017Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    Blitzortung is a non-commercial lightning detection system intended for recreational use only. In this thesis the performance of the Blitzortung system is evaluated in order to see to which extent it can be compared to a high performance commercial lightning detection system for use in Sweden. Also a graphical tool for visualising lightning strikes detected by Blitzortung on maps containing an electric grid with the related infrastructure is proposed.

    The evaluation is accomplished by comparing lightning data registered by Blitzortung with lightning data from the national lightning locating system provided by the Swedish meteorological institute. By analysing lightning data from the lightning high-season in Sweden between the year 2012-2016, and by conducting a more in depth evaluation of the system based on data from 2016, the Blitzortung system performance is evaluated.

    Results for calculated flash density and flash rate density suggests that the Blitzortung system is improving over the study time, which is probably due to the fact that the number of sensors in Sweden has increased from a single station in 2012 to 30 stations in 2016. The performance evaluation show a relative detection efficiency of 34 % for strokes correlated between the systems in relation to the total strokes detected by SMHI. For strokes detected south of latitude 61 in Sweden the relative DE (detection efficiency) is 44.7 %, and for CG(cloud-toground) strokes it is 43.0 %. If only CG-strokes south of latitude 61 is considered the corresponding value is 55.1 %. The performance of the Blitzortung-system seems to be depending on the number of sensors in the region of interest. The relative positional error between the networks south of latitude 61 was shown to have a smaller median error of 1750 m and an upper quartile on 3350 m, compared to north of latitude 61 where the median error was 2780 m and the upper quartile 5900 m.

    The results indicates a systematic directional error for correlated strokes between the systems. It is also shown that the included parameters for Blitzortung strokes could not be used in any meaningful way for predicting positional errors between the networks.

    Fulltekst (pdf)
    Utvardering-Blitzortung_Bergman
  • 232.
    Bergman, Anton
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Energi analysering och optimering av kyl- och värmesystem2017Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    The thesis project aims to investigate and analyze existing heating and cooling systems in public places and homes in Nordic countries from energy consumption aspects, and suggest possible optimized solutions to reduce their energy consumption. It was conducted, in particular, based on an average sized grocery store on Åland. The investigation and analysis have shown that the consumption of district heating was causing a high and unnecessary bill.

    Through a few coarse adjustments of control parameters in the control software for the cooling and heating system, we could maintain a lower consumption of district heat by 13%. These adjustments are just the beginning of what has been accomplished in terms of optimization. This is pleasing in the short term, but it is hard to certify if the changes will maintain the satisfying results under a longer period.

    For improvement and further work for optimization, data over a longer term, preferably a couple of months and most preferably one year, are needed. The data on temperatures for both setpoint and actual value may be logged every minute to get good and soft trend lines to follow. With trend lines for both inheritance and setpoint, optimized regulation can be made.

    Fulltekst (pdf)
    fulltext
  • 233.
    Bernhoff, H
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Review of electric energy storage2002Rapport (Annet vitenskapelig)
  • 234.
    Bernhoff, H
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Sjöstedt, E
    Leijon, M
    Wave energy resources in sheltered sea areas: A case study of the Baltic Sea2003Inngår i: Fifth European wave energy conference 17-19 Sept, 2003Konferansepaper (Annet vitenskapelig)
  • 235.
    Bernhoff, Hans
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Leijon, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. Avdelningen för elektricitetslära och åskforskning.
    Conversion of wave energy to electricity2004Inngår i: Scandinavian Shipping Gazette, nr October 1Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 236.
    Bilock, Alexander
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Probabilistic Approach to InsulationCoordination2016Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    The present work was performed at HVDC

    ABB as an initial study on how to adopt

    probabilistic concepts into the VCSHVDC

    insulation coordination.

    Due to large voltage levels in HVDC

    applications the corresponding

    insulation need to be properly

    addressed to ensure a safe, economical

    and reliable operation. Traditionally,

    only the maximum overvoltage is

    considered, where no adoption to the

    shape of the overvoltage distribution

    is regarded. Use of probabilistic

    concepts in the insulation coordination

    procedure can ideally reduce insulation

    margins with a maintained low risk of

    flashover. Analysis and understanding

    of probabilistic concepts of AC systems

    is needed in order to implement the

    concepts into VSC-HVDC.

    With use of advanced VSC-HVDC models,

    faults are simulated with varied fault

    insertion time in PSCAD. The resulting

    overvoltages from the simulation is

    gathered using different statistical

    methods in order to obtain the

    approximated overvoltage distribution.

    It was found from the simulation

    results that use of a Gaussian

    distribution is inappropriate due to

    shape variety in the overvoltage

    distributions. Instead, Kernel Density

    Estimate can serve as a flexible tool

    to approximate overvoltage

    distributions with a variety in number

    of modes and shape. The retrieved

    approximated overvoltage distributions

    are compared with the insulation

    strength in order to calculate the risk

    of flashover. The comparison shows that

    the insulation can be tuned in order to

    match set requirements. The thesis work

    should be seen as pilot study, where

    key problems have been pointed out and

    recommended further studies are

    proposed.

    Fulltekst (pdf)
    fulltext
  • 237.
    Bizzozero, Federica
    et al.
    Polytechnic University of Milan, Dipartimento Elettron Informaz & Bioingn.
    Bozzi, Silvia
    Polytechnic University of Milan, Dipartimento Elettron Informaz & Bioingn.
    Gruosso, Giambattista
    Polytechnic University of Milan, Dipartimento Elettron Informaz & Bioingn.
    Passoni, Giuseppe
    Polytechnic University of Milan, Dipartimento Elettron Informaz & Bioingn.
    Giassi, Marianna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära. mariarma.giassi@angstrom.uu.se.
    Spatial interactions among oscillating wave energy converters: electricity production and power quality issues2016Inngår i: Proceedings Of The Iecon 2016 - 42Nd Annual Conference Of The Ieee Industrial Electronics Society, IEEE, 2016, s. 4235-4240Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Point absorbers, i.e. wave energy converters (WECs) whose characteristic dimensions are small with respect to the typical wavelength, are designed to be installed in arrays, in order to get a cost-effective power generation. Starting from a coupled hydrodynamic electromagnetic model of a heaving point absorber, this paper presents an in-depth analysis of the hydrodynamic interactions among devices in array. The final goal is to find out the configurations of a four WEC array, which maximize the energy absorption and the quality of the power output. At this aim, different topological layouts, distances among converters and incident wave directions are investigated. The results highlight that a proper design of the wave farms allows to significantly reduce power fluctuations without negative side effects on electricity production.

  • 238.
    Björk, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Analys av stationsreglering vid Forsmarks kärnkraftverk: koppling mot eldynamiska simuleringsverktyg och modeller2016Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    This master thesis is done within the Energy Systems Engineering program at Uppsala University and performed for Forsmarks Kraftgrupp, Vattenfall. The nuclear power plant at Forsmark consists of three BWR units and is an important component in the Swedish power system. The nuclear power units are individually connected to the 400 kV transmission grid to export their production, but also to supply the units with auxiliary power when needed. As a backup the units are also connected to the 70 kV grid and each have several sub grids supported by backup diesel engines and batteries.This is to guarantee that the nuclear power units always have electrical power to support their vital auxiliary systems.

    To evaluate the function of the separate local power grids of Forsmark’s nuclear units and their interaction with the offsite grid, the simulation software Simpow have been used. With Simpow, the function of controllers, pumps and motors, vital for the plants safety, can be analyzed for different operation conditions and plant changes. Today the Electrical Power Analysis and Plant Engineering Group are in the process of changing from Simpow to new simulation software, PowerFactory. During this process the question of how to best implement the plant controller have been raised. The plant controller controls the thermal power, pressure and water level of the reactor, all contributing to the dynamics of the units power supply during operation. An implementation of the plant controller exist in Simpow for the plant’s older units Forsmark 1 and 2, but for the newest unit Forsmark 3 there is only a standard model of a steam turbine with governor implemented.

    In this thesis the effect of the plant controller systems are investigated to serve as a basis for implementation of the plants dynamics in the modelling of Forsmark 3 in PowerFactory.

    Fulltekst (pdf)
    fulltext
  • 239.
    Björkelund de Faire, Elias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Implementering av mjukvarubaserat PLC-system för reglering av magnetiseringen av en synkrongenerator2011Independent thesis Basic level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    In order to reduce the price for, and improve the performance of automatic control systems for magnetization of synchronus generators, the possibilities of using a PC based software PLC system, Programmable Logic Controller, has been investigated. The result is a system based on the CoDeSys software PLC with runtime environment from 3S-Software, communicating with external units via Modbus fieldbus. System price is reduced from €5000 to €2000 and system processing speed is reduced from 10 ms for a Siemens S7 PLC to 4 ms with the CoDeSys PLC system though unsolved problems with runtime seizure caused by improper settings in the PC BIOS.

    Fulltekst (pdf)
    fulltext
  • 240.
    Björlin Svozil, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    The Distribution System Operator: A Changing Role2013Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    With the introduction of distributed generation and

    information and communication technology the

    distribution system operator need to adapt to the

    changing circumstances of the market place. This has

    put requirements on the distribution system operator

    to transform from a passive management philosophy

    and become pro-active in its management of the

    system.

    The aim of this report is to investigate how the

    changing market place will put new requirements on

    the distribution system operator and how it will

    transform its business model.

    The pro-active distribution system operator will have

    to manage new type of consumers (Prosumer, DGO/

    Aggregator, TSO) with different contracts and new

    consumer relationships. These new consumers will be

    in need of faster (real-time) and more transparent

    information in order to support the system and its

    system services.

    The Distribution system operator will have to

    transform from being passive and become pro-active

    in order to solve the new requirements that it will

    face, in order to produce value for its consumers and

    partners.

    Fulltekst (pdf)
    fulltext
  • 241. Blackmore, T.
    et al.
    Batten, W. M. J.
    Bahaj, A. S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Inlet grid-generated turbulence for large-eddy simulations2013Inngår i: International journal of computational fluid dynamics (Print), ISSN 1061-8562, E-ISSN 1029-0257, Vol. 27, nr 6-7, s. 307-315Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new technique of generating turbulence in large-eddy simulations (LES) has been investigated and results compared with previous studies for validation. The proposed gridInlet technique uses a grid pattern on the inlet boundary patch to produce grid-generated turbulence as used in wind tunnel experiments. This allows the turbulence integral length scale to be controlled by changing the grid size, while the turbulence intensity is controlled by changing the inlet distance. The objective of this paper is to investigate domain and mesh requirements to implement the gridInlet technique. This technique is most suited to studies on the influence of high-intensity isotropic turbulence on objects, particularly if comparisons are to be made to experimental data obtained with grid-generated turbulence.

  • 242. Blackmore, Tom
    et al.
    Batten, WilliamM J.
    Műller, GeraldU
    Bahaj, AbuBakrS
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Influence of turbulence on the drag of solid discs and turbine simulators in a water current2013Inngår i: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 55, nr 1, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laboratory experiments have been used to investigate the effects of turbulence on the drag of both solid discs and porous disc turbine simulators. These discs were introduced to turbulent flows, in a gravity-fed water flume, with various levels of turbulence intensity and integral length scales. The turbulence was generated using three different grid configurations, which produced intensities and scales comparable with previous wind tunnel studies. The drag measurements were taken with discs of two different diameters and porosities with and without the upstream grids. The experimental results have demonstrated that the drag coefficients, of all the discs tested, are significantly dependent on both the turbulence intensity and integral length scale. For small integral length scales, relative to the disc, the drag coefficients converged for turbulence intensities greater than 13 %, with an increase of around 20 % in drag coefficient over the low-intensity case. Experiments with turbulence intensities of 10 % demonstrated minimum drag coefficients when the integral length scale-to-disc diameter ratio was around 50 %. Significant variations in the drag coefficient of circular bluff bodies are therefore expected when operating in turbulent flows with different characteristics.

  • 243. Blackmore, Tom
    et al.
    Batten, W.M.J.
    Bahaj, A.S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Turbulence generation and its effect in LES approximations of tidal turbines2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Tidal flows suitable for the installation of tidal stream turbines are highly turbulent with a broad range of turbulent scales, and intensities of around 10%. It is important to understand how turbulent flows affect the performance and wake profiles for the accurate prediction of the performance of single devices and arrays. Previous studies have considered the effects of turbulence intensity, but the effects of turbulent eddy size have not been investigated. This paper presents a new method for generating turbulence in large eddy simulations of uniform actuator disc rotor models. The advantage of the gridded actuator disc is that the generated turbulence may be controlled, so the effects of turbulence length scale and intensity may be investigated. Initial results show the wake recovery is faster behind a rotor generating larger turbulent length scales and intensities, with a corresponding increase in axial induction and thrust. Therefore turbines may be positioned closer together if they generate more turbulence, increasing the power output of an array for a given area, although the individual device performance may be lower. Future work will consider the effects of free-stream turbulence on the performance and wake profiles of the gridded actuator disc, and validation against experimental data.

  • 244.
    Bladh, Johan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Hydropower generator and power system interaction2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    After decades of routine operation, the hydropower industry faces new challenges. Large-scale integration of other renewable sources of generation in the power system accentuates the role of hydropower as a regulating resource. At the same time, an extensive reinvestment programme has commenced where many old components and apparatus are being refurbished or replaced. Introduction of new technical solutions in existing power plants requires good systems knowledge and careful consideration. Important tools for research, development and analysis are suitable mathematical models, numerical simulation methods and laboratory equipment. This doctoral thesis is devoted to studies of the electromechanical interaction between hydropower units and the power system. The work encompasses development of mathematical models, empirical methods for system identification, as well as numerical and experimental studies of hydropower generator and power system interaction. Two generator modelling approaches are explored: one based on electromagnetic field theory and the finite element method, and one based on equivalent electric circuits. The finite element model is adapted for single-machine infinite-bus simulations by the addition of a network equivalent, a mechanical equation and a voltage regulator. Transient simulations using both finite element and equivalent circuit models indicate that the finite element model typically overestimates the synchronising and damping properties of the machine. Identification of model parameters is performed both numerically and experimentally. A complete set of equivalent circuit parameters is identified through finite element simulation of standard empirical test methods. Another machine model is identified experimentally through frequency response analysis. An extension to the well-known standstill frequency response (SSFR) test is explored, which involves measurement and analysis of damper winding quantities. The test is found to produce models that are suitable for transient power system analysis. Both experimental and numerical studies show that low resistance of the damper winding interpole connections are vital to achieve high attenuation of rotor angle oscillations. Hydropower generator and power system interaction is also studied experimentally during a full-scale startup test of the Nordic power system, where multiple synchronised data acquisition devices are used for measurement of both electrical and mechanical quantities. Observation of a subsynchronous power oscillation leads to an investigation of the torsional stability of hydropower units. In accordance with previous studies, hydropower units are found to be mechanically resilient to subsynchronous power oscillations. However, like any other generating unit, they are dependent on sufficient electrical and mechanical damping. Two experimentally obtained hydraulic damping coefficients for a large Francis turbine runner are presented in the thesis.

    Delarbeid
    1. Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
    Åpne denne publikasjonen i ny fane eller vindu >>Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
    2016 (engelsk)Inngår i: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, nr 1, s. 46-56Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-182155 (URN)10.1109/TEC.2015.2450994 (DOI)000372024100005 ()
    Eksternt samarbeid:
    Tilgjengelig fra: 2012-10-04 Laget: 2012-10-04 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    2. Torsional stability of hydropower units under influence of subsynchronous oscillations
    Åpne denne publikasjonen i ny fane eller vindu >>Torsional stability of hydropower units under influence of subsynchronous oscillations
    2013 (engelsk)Inngår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, nr 4, s. 3826-3833Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-182150 (URN)10.1109/TPWRS.2013.2263811 (DOI)000326184100032 ()
    Tilgjengelig fra: 2013-10-17 Laget: 2012-10-04 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    3. Synchronised measurements on hydropower units during power system startup
    Åpne denne publikasjonen i ny fane eller vindu >>Synchronised measurements on hydropower units during power system startup
    (engelsk)Inngår i: Hydro Review Worldwide, ISSN 1072-9542Artikkel i tidsskrift (Fagfellevurdert) Submitted
    Abstract [en]

    During a recent full-scale blackstart test of the Nordic power system, measurements of electrical and mechanical quantities using both phasor measurement units (PMUs) and synchronised local acquisition devices was performed. This paper describes the measurement system and discusses a few important considerations for synchronised measurements in multiple hydropower stations. One generator's response to a \unit[100]{MW} load step is shown and an observed subsynchronous oscillation is discussed. It is shown that comprehensive measurements using multiple synchronised data acquisition devices can be performed using off-the-shelf hardware and existing infrastructure. The findings show the danger of assuming that all the interesting information is found at the fundamental frequency.

    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-182157 (URN)
    Tilgjengelig fra: 2012-10-04 Laget: 2012-10-04 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    4. Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests
    Åpne denne publikasjonen i ny fane eller vindu >>Estimation of Hydropower Generator Parameters Through Field Simulations of Standard Tests
    2010 (engelsk)Inngår i: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 25, nr 4, s. 931-939Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    Emneord
    Applied voltage tests, finite-element (FE) methods, parameter estimation, short-circuit tests, slip tests, synchronous generators
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-139402 (URN)10.1109/TEC.2010.2064776 (DOI)000284415900002 ()
    Tilgjengelig fra: 2010-12-27 Laget: 2010-12-23 Sist oppdatert: 2018-02-05bibliografisk kontrollert
    5. Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
    Åpne denne publikasjonen i ny fane eller vindu >>Use of a finite element model for the determination of damping and synchronizing torques of hydroelectric generators
    2013 (engelsk)Inngår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 44, nr 1, s. 844-851Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    Emneord
    Damping torque, finite element method, single-machine infinite bus system, synchronizing torque, synchronous machines
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-182158 (URN)10.1016/j.ijepes.2012.08.027 (DOI)000311864800094 ()
    Tilgjengelig fra: 2012-10-04 Laget: 2012-10-04 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    6. Comparison of field and circuit generator models in single machine infinite bus system simulations
    Åpne denne publikasjonen i ny fane eller vindu >>Comparison of field and circuit generator models in single machine infinite bus system simulations
    2010 (engelsk)Inngår i: Electrical Machines (ICEM), 2010 XIX International Conference on, 2010Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

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

    Emneord
    damping, equivalent circuits, finite element analysis, rotors, synchronous generators, transient response, circuit generator model, circuit model parameter estimation, electromagnetic model, equivalent circuit representation, field generator model, finite element salient pole synchronous generator model, infinite network bus, machine damping property, machine stiffness property, rotor circuit, single machine infinite bus system simulations
    HSV kategori
    Forskningsprogram
    Teknisk fysik med inriktning mot elektricitetslära
    Identifikatorer
    urn:nbn:se:uu:diva-140377 (URN)10.1109/ICELMACH.2010.5608259 (DOI)
    Konferanse
    XIX International Conference on Electrical Machines (ICEM)
    Tilgjengelig fra: 2011-01-05 Laget: 2011-01-05 Sist oppdatert: 2018-02-05
    7. Effects of including automatic excitation control in transient field simulations of hydrogenerators
    Åpne denne publikasjonen i ny fane eller vindu >>Effects of including automatic excitation control in transient field simulations of hydrogenerators
    2009 (engelsk)Inngår i: Proceedings of the 44th International Universities Power Engineering Conference, University of Strathclyde Glasgow, 2009Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    University of Strathclyde Glasgow: , 2009
    Emneord
    Electrical Machines and Drives, Generator dynamics and control 2
    HSV kategori
    Identifikatorer
    urn:nbn:se:uu:diva-121652 (URN)
    Konferanse
    UPEC 2009
    Tilgjengelig fra: 2010-03-26 Laget: 2010-03-26 Sist oppdatert: 2018-02-05bibliografisk kontrollert
    Fulltekst (pdf)
    fulltext
  • 245.
    Bladh, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Lundin, Urban
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Synchronised measurements on hydropower units during power system startupInngår i: Hydro Review Worldwide, ISSN 1072-9542Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During a recent full-scale blackstart test of the Nordic power system, measurements of electrical and mechanical quantities using both phasor measurement units (PMUs) and synchronised local acquisition devices was performed. This paper describes the measurement system and discusses a few important considerations for synchronised measurements in multiple hydropower stations. One generator's response to a \unit[100]{MW} load step is shown and an observed subsynchronous oscillation is discussed. It is shown that comprehensive measurements using multiple synchronised data acquisition devices can be performed using off-the-shelf hardware and existing infrastructure. The findings show the danger of assuming that all the interesting information is found at the fundamental frequency.

  • 246. Bladh, Johan
    et al.
    Sundqvist, Per
    Lundin, Urban
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Torsional stability of hydropower units under influence of subsynchronous oscillations2013Inngår i: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 28, nr 4, s. 3826-3833Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 247.
    Bladh, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Wallin, Mattias
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Saarinen, Linn
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Lundin, Urban
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements2016Inngår i: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 31, nr 1, s. 46-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 248.
    Blennow, HJM
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för materialvetenskap. Institutionen för teknikvetenskaper, Elektricitetslära. DIVISION FOR ELECTRICITY AND LIGHTNING RESEARCH.
    Leijon, M
    Gubanski, SM
    Active high voltage insulation2002Inngår i: Journal of Electrostatics, Vol. 55, nr 2, s. 111-223Artikkel i tidsskrift (Fagfellevurdert)
  • 249.
    Blomström, Hanna
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Effektiviseringspotential inom industrisektorn: Energibesparing vid frekvensstyrning av centrifugalpumpar – en fallstudie2013Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    The project was performed at Siemens

    Industry Drive Technologies with the

    objective to provide actual values for

    the energy savings potential within

    Siemens scope of practice.

    In Sweden the electrical drives stand

    for about 30 % of the total electricity

    consumption and about 60 % of the

    electricity consumption within the

    industry. During the pre-study phase

    electrical drives with pump applications

    were identified as large energy users.

    Because of this a case study at one of

    Siemens customers, Stora Enso Fors was

    performed. The system that was evaluated

    during the case study was a throttled

    system with a centrifugal pump for

    pumping pulp.

    The results yielded that a saving of

    over 50 % could be achieved by replacing

    the throttle valve with a variable speed

    drive, a frequency converter. The

    payback period was two years and two

    months and the present value for the

    total life cycle cost of the variable

    speed system was 662.566 SEK lower than

    for the throttled system. As a

    consequence, Stora Enso Fors is advised

    to invest in a frequency converter for

    regulation of the system.

    The general conclusion is that a focus

    on system efficiency is the most

    important factor in energy efficiency

    projects and that the system regulation

    method has a large impact on the overall

    system losses and hence its efficiency.

    Energy efficiency potential for

    throttled systems with centrifugal pumps

    is large and significant economical

    savings can be made through investments

    with short payback time.

    Fulltekst (pdf)
    fulltext
  • 250. Blunden, L. S.
    et al.
    Bahaj, A. S.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Aziz, N. S.
    Tidal current power for Indonesia? An initial resource estimation for the Alas Strait2013Inngår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 49, nr 0, s. 137-142Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Indonesia – with its many narrow straits and significant tidal range – might be expected to have considerable potential for tidal current power generation. A particularly promising site is the Alas Strait, with shallow depth, high tidal current velocity and location far from major shipping lanes. In this study, a hydrodynamic numerical model of the Alas Strait was run and validated against some tidal current velocity measurements. The results of the model were then used to estimate the practically exploitable energy resources in the strait, using a development of a method used in previous resource estimations. In this method, the incident velocity on each row of an array was extracted from the model and then attenuated based on the direction of the flow and the number of rows deep into the array. In this way, the effects of practical array shape can be simulated without the need to include computationally expensive parameterization of turbines in the model. Two scenarios were considered, with and without a maximum depth limitation of 40 m. The first scenario gave an estimate of the practically exploitable annual energy yield from the Alas Strait of 330 GW h with the second scenario nearly double at 640 GW h.

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