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Electromagnetic dispersion modeling and analysis for HVDC power cables
Linnaeus University, Faculty of Science and Engineering, School of Computer Science, Physics and Mathematics.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Derivation of an electromagnetic model, regarding the wave propagation in a very long (10 km or more) High Voltage Direct Current (HVDC) power cable, is the central part of this thesis. With an existing “perfect” electromagnetic model there are potentially a wide range of applications.The electromagnetic model is focused on frequencies between 0 and 100 kHz since higher frequencies essentially will be attenuated. An exact dispersion relation is formulated and the propagation constant is computed numerically. The dominating mode is the first Transversal Magnetic (TM) mode of order zero, denoted TM01, which is also referred to as the quasi-TEM mode. A comparison is made with the second propagating TM mode of order zero denoted TM02. The electromagnetic model is verified against real time data from Time Domain Reflection (TDR) measurements on a HVDC power cable. A mismatch calibration procedure is performed due to matching difficulties between the TDR measurement equipment and the power cable regarding the single-mode transmission line model.An example of power cable length measurements is addressed, which reveals that with a “perfect” model the length of an 80 km long power cable could be estimated to an accuracy of a few centimeters. With the present model the accuracy can be estimated to approximately 100 m.In order to understand the low-frequency wave propagation characteristics, an exact asymptotic analysis is performed. It is shown that the behavior of the propagation constant is governed by a square root of the complex frequency in the lowfrequency domain. This thesis also focuses on an analysis regarding the sensitivity of the propagation constant with respect to some of the electric parameters in the model. Variables of interest when performing the parameter sensitivity study are the real relative permittivityand the conductivity.

Place, publisher, year, edition, pages
Växjö, 2012. , 10 p.
Keyword [en]
HVDC power cables, electromagnetic model, TDR measurement, sensitivity analysis, dispersion relation, propagation constant, low-frequency asymptotics
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:lnu:diva-32525OAI: oai:DiVA.org:lnu-32525DiVA: diva2:700037
Presentation
2012-12-11, D1136, Växjö, 13:15 (English)
Opponent
Supervisors
Available from: 2014-08-19 Created: 2014-02-27 Last updated: 2014-08-19Bibliographically approved
List of papers
1. Electromagnetic dispersion modeling and measurements for HVDC power cables
Open this publication in new window or tab >>Electromagnetic dispersion modeling and measurements for HVDC power cables
2011 (English)Report (Other academic)
Abstract [en]

This paper provides a general framework for electromagnetic modeling, computation and measurements regardingthe 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 andthe 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 aspectsregarding 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 cableand the instrumentation.A mismatch calibration procedure is therefore devised to account for the connection between the measurement equipmentand 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 discussedand analyzed using statistical methods based on the Cram\'{e}r-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 givenmeasurement data is in the order of centimeters.

Publisher
40 p.
National Category
Engineering and Technology
Research subject
Physics, Electrotechnology
Identifiers
urn:nbn:se:lnu:diva-14989 (URN)
Available from: 2011-10-18 Created: 2011-10-17 Last updated: 2017-01-10Bibliographically approved
2. Low-frequency dispersion characteristics of a multilayered coaxial cable
Open this publication in new window or tab >>Low-frequency dispersion characteristics of a multilayered coaxial cable
Show others...
2013 (English)In: Journal of Engineering Mathematics, ISSN 0022-0833, E-ISSN 1573-2703, Vol. 83, no 1, 169-184 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Springer Netherlands, 2013
National Category
Mathematics Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-25989 (URN)10.1007/s10665-012-9616-3 (DOI)000327855300009 ()2-s2.0-84888434349 (Scopus ID)
Available from: 2013-05-31 Created: 2013-05-31 Last updated: 2017-12-06Bibliographically approved
3. Electromagnetic dispersion modeling and sensitivity analysis for HVDC power cables
Open this publication in new window or tab >>Electromagnetic dispersion modeling and sensitivity analysis for HVDC power cables
2012 (English)Report (Other academic)
Abstract [en]

This paper addresses electromagnetic wave propagation in High Voltage Direct Current (HVDC) power cables. An electromagnetic model, based on long (10 km or more) cables with a frequency range of 0 to 100 kHz, is derived. Relating the frequency to the propagation constant a dispersion relation is formulated using a recursive approach. The propagation constant is found numerically with normalized residue calculation. The paper is concluded with a sensitivity analysis of the propagation constant with respect to the electrical parameters εr (the real relative permittivity) and σ (the conductivity)

Place, publisher, year, edition, pages
Växjö: Linnaeus University, Scool of Computer Science, Physics and Mathematics, 2012
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:lnu:diva-22296 (URN)
Available from: 2012-11-14 Created: 2012-11-06 Last updated: 2017-01-10Bibliographically approved
4. Electromagnetic dispersion modeling and measurements for HVDC power cables
Open this publication in new window or tab >>Electromagnetic dispersion modeling and measurements for HVDC power cables
Show others...
2014 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 29, no 6, 2439-2447 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE Press, 2014
National Category
Signal Processing
Research subject
Physics, Waves and Signals
Identifiers
urn:nbn:se:lnu:diva-27494 (URN)10.1109/TPWRD.2014.2324181 (DOI)000345513600003 ()2-s2.0-84913596312 (Scopus ID)
Available from: 2013-07-09 Created: 2013-07-09 Last updated: 2017-12-06Bibliographically approved

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