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1.
  • Nordebo, Sven, et al. (författare)
  • Electromagnetic dispersion modeling and measurements for HVDC power cables
  • 2011
  • Rapport (övrigt vetenskapligt)abstract
    • This paper provides a general framework for electromagnetic modeling, computation and measurements regarding the wave propagation characteristics of High-Voltage Direct Current (HVDC) power cables. The modeling is focused on very long (10 km or more) HVDC power cables and the relevant frequency range is therefore in the low-frequency regime of about 0-100 kHz. An exact dispersion relation is formulated together with a discussion on practical aspects regarding the computation of the propagation constant and the related characteristic impedance. Experimental time-domain measurement data from an 80 km long HVDC power cable is used to validate the model. It is concluded that a single-mode transmission line model is not adequate to account for the mismatch between the power cable and the instrumentation. A mismatch calibration procedure is therefore devised to account for the connection between the measurement equipment and the cable. A dispersion model is thus obtained that is accurate for early times of pulse arrival. To highlight the potential of accurate electromagnetic modeling, an example of high-resolution length-estimation is discussed and analyzed using statistical methods based on the Cramer-Rao lower bound. The analysis reveals that the estimation accuracy based on the present model (and its related model error) is in the order of 100 m for an 80 km long power cable, and that the potential accuracy using a perfect model based on the given measurement data is in the order of centimeters.
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3.
  • Nordebo, Sven, et al. (författare)
  • Low-frequency dispersion characteristics of a multilayered coaxial cable
  • 2013
  • Ingår i: Journal of Engineering Mathematics. - Springer Netherlands. - 0022-0833. ; 83:1, s. 169-184
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper provides an exact asymptotic analysis regarding the low-frequency dispersion characteristics of a multilayered coaxial cable. A layer-recursive description of the dispersion function is derived that is well suited for asymptotic analysis. The recursion is based on two well-behaved (meromorphic) subdeterminants defined by a perfectly electrically conducting (PEC) and a perfectly magnetically conducting termination, respectively. For an open waveguide structure, the dispersion function is a combination of two such functions, and there is only one branch point that is related to the exterior domain. It is shown that if there is one isolating layer and a PEC outer shield, then the classical Weierstrass preparation theorem can be used to prove that the low-frequency behavior of the propagation constant is governed by the square root of the complex frequency, and an exact analytical expression for the dominating term of the asymptotic expansion is derived. It is furthermore shown that the same asymptotic expansion is valid to its lowest order even if the outer shield has finite conductivity and there is an infinite exterior region with finite nonzero conductivity. As a practical application of the theory, a high-voltage direct current (HVDC) power cable is analyzed and a numerical solution to the dispersion relation is validated by comparisons with the asymptotic analysis. The comparison reveals that the low-frequency dispersion characteristics of the power cable is very complicated and a first-order asymptotic approximation is valid only at extremely low frequencies (below 1 Hz). It is noted that the only way to come to this conclusion is to actually perform the asymptotic analysis. Hence, for practical modeling purposes, such as with fault localization, an accurate numerical solution to the dispersion relation is necessary and the asymptotic analysis is useful as a validation tool.
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5.
  • Nordebo, Sven, et al. (författare)
  • Wave modeling and fault localization for underwater power cables
  • 2011
  • Ingår i: 2011 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC). - 978-1-4577-0046-0 ; s. 698-701
  • Konferensbidrag (refereegranskat)abstract
    • This paper describes some preliminary results regarding Time-Domain pulse Reflection (TDR) measurements and modeling performed on the Baltic Cable submarine HVDC link between southern Sweden and northern Germany. The measurements were conducted in collaboration between the Linnaeus University, Lund University, Baltic Cable AB and ABB High Voltage Cables AB, and is part of the research project: “Fundamental wave modeling for signal estimation on lossy transmission lines”. Preliminary results on measurements and modeling are included here, as well as a first numerical study regarding the low-frequency dispersion characteristics of power cables. The numerical study shows that the finite conductivity of the cable lead shield has a great impact on the losses at low frequencies (0-1 kHz), and that the low-frequency asymptotics of the propagation constant is consistent with common propagation models based on the skin-effect.
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6.
  • Andersson, Mats R., et al. (författare)
  • Electroluminescence from Substituted Poly(thiophenes) : From Blue to Near-Infrared
  • 1995
  • Ingår i: Macromolecules. - American Chemical Society. - 0024-9297. ; 28:22, s. 7525-7529
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a systematic approach to the control of the conjugation length along the poly(thiophene) backbone. The planarity of the main chain can be permanently modified by altering the pattern of substitution and character of the substituents on the poly(thiophene) chain, and the conjugation length is thus modified. We obtain blue, green, orange, red, and near-infrared electroluminescence from four chemically distinct poly(thiophenes). The external quantum efficiencies are in the range of 0.01-0.6%.
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7.
  • Bogren, Jörgen, 1961-, et al. (författare)
  • Tema Vintermodell
  • 2006
  • Rapport (övrigt vetenskapligt)abstract
    • Syftet med Vintermodellen är att beräkna och värdera de väsentligaste konsekvenserna för trafikanter, väghållare och samhälle av olika strategier och åtgärder inom vinterväghållningen. Huvudrapporten är i sig en sammanfattning av de rapporter som beskriver Vintermodellens olika delmodeller. Navet i Vintermodellen är Väglagsmodellen, som utgående från väderdata, vidtagna väghållningsåtgärder och trafik beräknar väglaget timme för timme under vintersäsongen. Väglagsmodellen styr beräkningarna i de olika effektmodellerna: Olycksmodellen, Framkomlighetsmodellen, Fordonskostnadsmodellen, Miljömodellen och Modellen för väghållarkostnader. I Olycksmodellen beräknas olyckskvoter, olyckstyper och konsekvenser, allt kopplat till olika väglag och deras varaktigheter.I Framkomlighetsmodellen beräknas olika väglags effekt på medelhastigheter och restider.I Fordonskostnadsmodellen beräknas kostnader för bränsleförbrukning och korrosion på grund av vägsalt.I Miljömodellen beräknas konsekvenserna för vägnära vegetation av vägsalt.I Modellen för väghållarkostnader beräknas dels direkta kostnader för åtgärderna, dels kostnader för skador och slitage på beläggning, vägmarkeringar etc. som följd av vinterväghållningsåtgärder.
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