| 1. |
- Gustafsson, Stefan, et al.
(författare)
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Electromagnetic dispersion modeling and measurements for HVDC power cables
- 2014
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Ingår i: IEEE Transactions on Power Delivery. - : IEEE Press. - 0885-8977 .- 1937-4208. ; 29:6, s. 2439-2447
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a general framework for electromagnetic (EM) modeling, sensitivity analysis, computation, and measurements regarding the wave propagation characteristics of high-voltage direct-current (HVDC) power cables. The modeling is motivated by the potential use with transient analysis, partial-discharge measurements, fault localization and monitoring, and is focused on very long (10 km or more) HVDC power cables with transients propagating 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. Experimental time-domain measurement data from an 80-km-long HVDC power cable are used to validate the electromagnetic model, and a mismatch calibration procedure is devised to account for the connection between the measurement equipment and the cable. Quantitative sensitivity analysis is devised to study the impact of parameter uncertainty on wave propagation characteristics. The sensitivity analysis can be used to study how material choices affect the propagation characteristics, and to indicate which material parameters need to be identified accurately in order to achieve accurate fault localization. The analysis shows that the sensitivity of the propagation constant due to a change in the conductivity in the three metallic layers (the inner conductor, the intermediate lead shield, and the outer steel armor) is comparable to the sensitivity with respect to the permittivity of the insulating layer. Hence, proper modeling of the EM fields inside the metallic layers is crucial in the low-frequency regime of 0-100 kHz.
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| 2. |
- Nordebo, Sven, et al.
(författare)
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Electromagnetic dispersion modeling and measurements for HVDC power cables
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)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)
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Low-frequency dispersion characteristics of a multilayered coaxial cable
- 2013
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Ingår i: Journal of Engineering Mathematics. - : Springer Netherlands. - 0022-0833 .- 1573-2703. ; 83:1, s. 169-184
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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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| 4. |
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| 5. |
- Nordebo, Sven, et al.
(författare)
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Wave modeling and fault localization for underwater power cables
- 2011
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Ingår i: 2011 IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications (APWC). - : IEEE Press. - 9781457700460 ; , s. 698-701
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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. |
- Gustafsson, Mats, et al.
(författare)
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A time-domain approach to the extinction paradox for scattering of electromagnetic waves
- 2008
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Ingår i: ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- The extinction paradox states that a perfectly electric conducting target which is large compared to the wavelength removes from the incident radiation exactly twice the amount of power it can intercept by its geometrical cross section area. In this paper, the extinction paradox is generalized to include temporally dispersive material parameters with finite values of the permittivity and the permeability. From a time-domain approach it is shown that the high-frequency limit of the extinction cross section depends on the material parameters of the target and that a limiting value not necessarily exists. These findings are exemplified by several numerical illustrations with different values of the extinction cross section in the high-frequency limit.
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| 7. |
- Gustafsson, Mats, et al.
(författare)
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Design of frequency selective windows for improved indoor outdoor communication
- 2006
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 54:6, s. 1897-1900
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Tidskriftsartikel (refereegranskat)abstract
- The use of low emissivity windows degrades radio communication. This Communication presents design, manufacturing, and test measurements for an energy saving window that is transparent to GSM, GPS, and 3G radio wave frequencies. A frequency selective structure (FSS) is used in the metallic coating of the window to provide the desirable transparency in the frequency range from 900 MHz to 2 GHz. The periodic pattern used for the FSS is of the aperture type and the elements are hexagon loops. The FSS simulations are performed using the mode matching technique as well as the finite-difference time domain method. A frequency selective window was manufactured from a commercially available low emissivity glass. Measurements indicate that the frequency selective window has approximately 10 dB better transmission in the 900 MHz-2 GHz band than the original window.
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| 8. |
- Gustafsson, Mats, et al.
(författare)
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Design of Frequency Selective Windows for Improved Indoor Outdoor Communication
- 2005
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The use of low emissivity windows degrades radio communication. This paperpresents design, manufacturing and test measurements for an energy savingwindow that is transparent to GSM, GPS and 3G radio wave frequencies.A frequency selective structure (FSS) is used in the metallic coating of thewindow to provide the needed transparency that ranges from 900MHz to2GHz. The periodic pattern used for the FSS is of the aperture type and theelements are hexagon loops. FSS simulations are performed using two dierentmethods, namely the mode matching technique and the Finite-DierenceTime Domain method. A frequency selective window is manufactured from acommercially available low emissivity glass. Measurements indicate that thefrequency selective window shows an improvement of at least 10 dB in thetransmission over the original window.
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