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Techniques for Localization of Insulation Degradation along Medium-Voltage Power Cables
KTH, School of Electrical Engineering (EES).
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Time Domain Reflectometry (TDR) has been used for localization of transmission line discontinuities in diverse applications. Various challenges have to be addressed when applying TDR for localization of insulation degradation in power cables. The dominant problem is that TDR detects reflections coming from insulation changes, but it also records reflections related to geometrical irregularities along the cable length and, in some cases, surrounding medium variations. It is realized that one can compare TDR measurements before and after changes have occurred or have been induced in the aged sections. Thus the signals from the deteriorated insulation can be distinguished from other reflections that are constant.

The measurement technique to localize water-treeing in cross-linked polyethylene (XLPE) insulation is based on the voltage nonlinearity of water trees. TDR measurements have been performed before, after and during the application of high AC voltages. The high stresses affect the cable characteristic impedance and speed of wave propagation in the water-treed region. The possibility to detect local changes in the velocity of wave propagation has been presented as a technique for localization of insulation ageing. Localization of impedance changes related to water treeing and water ingress in mass impregnated paper insulated cables has also been achieved.

To characterize the power cables in the high frequency domain two parameter extraction methods have been developed. The first one uses TDR measurements and analyses short pulse propagation along the cable. The second one is based on the S-parameter measurements in the frequency domain. The methods extract the complex propagation constant and the characteristic impedance, as well as the LCRG Telegrapher's Equation parameters for the frequencies between 300 kHz and 300 MHz.

The dependence of the high frequency power cables properties on the metallic screen design and cable surrounding medium has been studied. The cable characteristics are modeled using time- and frequency-domain numerical simulations. This is required due to the complex spiralized structure of the outer metallic screen. It is established that this screen design causes a dependence of the cable characteristics on the surrounding medium.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , xii, 114 p.
Series
Trita-ETS, ISSN 1650-674X ; 2005:03
Keyword [en]
Electrical power technology, Attenuation measurement, cross-linked polyethylene insulation, discontinuities, localization, mass-impregnated insulation, numerical analysis, parameter estimation, power cable metallic screen, scattering parameters, time domain reflectometry, velocity measurements, water treeing
Keyword [sv]
Elkraftteknik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-207ISBN: 91-7178-044-0 (print)OAI: oai:DiVA.org:kth-207DiVA: diva2:7911
Public defence
2005-05-27, E1, Lindstedtsvägen 3, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101012Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2010-10-12Bibliographically approved
List of papers
1. Calibration for Time Domain Propagation Constant Measurements on Power Cables
Open this publication in new window or tab >>Calibration for Time Domain Propagation Constant Measurements on Power Cables
2003 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 52, no 2, 415-418 p.Article in journal (Refereed) Published
Abstract [en]

A method has been developed for characterizingthe wave propagation properties of medium voltage (MV) powercables. It delivers the complex propagation constant of lossy cabletransmission lines as a function of frequency. The technique isbased on time domain measurements and frequency domain analysisof short pulse propagation. Particular attention is paid to thecalibration, as samples with arbitrary characteristic impedancescan cause multiple reflections in the test setup. The influence ofnumerical artefacts is also investigated. The developed techniqueis demonstrated on MV crosslinked polyethylene (XLPE) cables.The results are verified by comparison with frequency domainmeasurements of the cable S-parameters.

Keyword
attenuation measurement, calibration, frequency domain analysis, scattering parameters, time domain reflectometry, transmission lines
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5120 (URN)10.1109/TIM.2003.811657 (DOI)000183212000046 ()
Note
QC 20101012Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
2. Extraction of the High Frequency Power Cable Characteristics from S-parameter Measurements
Open this publication in new window or tab >>Extraction of the High Frequency Power Cable Characteristics from S-parameter Measurements
Show others...
2004 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 11, no 3, 461-470 p.Article in journal (Refereed) Published
Abstract [en]

A technique is developed for extraction of the wave propagation properties of power cables from S-parameter measurements. The method extracts the complex propagation constant and the characteristic impedance, as well as the LCRG Telegrapher's Equation parameters. The extraction process is developed after clarifying the effect of the connection between the measurement port and the power cable. It is concluded that treating the connection solely as a characteristic impedance change could lead to considerable errors in the parameter extraction. Furthermore, the method corrects for electrical lengths, which are not accounted for by the standard Network Analyzer calibration. The extraction is demonstrated for a medium voltage crosslinked polyethylene (XLPE) cable over the frequency range 300 kHz to 300 MHz. The results are compared to a time domain short pulse propagation method for cable characterization. Both measurement methods are evaluated against a cable model.

Keyword
Attenuation measurement, Cross linked polyethylene insulation, Parameter estimation, Power cables, Scattering parameters
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5121 (URN)10.1109/TDEI.2004.1306724 (DOI)000222131200008 ()2-s2.0-3142739324 (Scopus ID)
Note
QC 20100914Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
3. High Frequency Characterisation of Water-treed XLPE Cables
Open this publication in new window or tab >>High Frequency Characterisation of Water-treed XLPE Cables
2003 (English)In: PROCEEDINGS OF THE 7TH INTERNATIONAL CONFERENCE ON PROPERTIES AND APPLICATIONS OF DIELECTRIC MATERIALS, VOLS 1-3, 2003, 187-190 p.Conference paper, Published paper (Refereed)
Abstract [en]

Time Domain Reflectometry (TDR) has been used for localisation of transmission line discontinuities in various applications. One of the challenges when applying TDR is to obtain knowledge of the high frequency characteristics of both the degraded and the undegraded sections of the cable. The wave propagation characteristics of water-treed XLPE cables are investigated in this study. The parameters are extracted from the cable S-parameters measured with a Network Analyzer (NA) in the frequency range from 300 kHz to 300 MHz. The cable samples are characterised at different temperatures and with different water content of the water trees. The effect of the application of nominal voltage for extended period on the cable wave propagation characteristics is also shown. High voltage dielectric spectroscopy is used as a reference method for estimation of the level of water tree deterioration.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5125 (URN)10.1109/ICPADM.2003.1218384 (DOI)000186114700045 ()0-7803-7725-7 (ISBN)
Conference
7th International Conference on Properties and Applications of Dielectric Materials NAGOYA, JAPAN, JUN 01-05, 2003
Note
QC 20101012Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2010-10-12Bibliographically approved
4. Wave Propagation on Power Cables with Special Regard to Metallic Screen Design
Open this publication in new window or tab >>Wave Propagation on Power Cables with Special Regard to Metallic Screen Design
2007 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 14, no 2, 409-416 p.Article in journal (Refereed) Published
Abstract [en]

The high frequency properties of coaxial power cables are modeled using time- and frequency-domain numerical simulations. This is required due to the complex helical structure of the outer metallic screen. The finite element (FEM) and finite difference time domain methods (FDTD) have been employed to study the effect of screen spiralization. It is established that this screen design causes a dependence of the cable high frequency characteristics on the surrounding medium. Analytical model based on modal analysis of wave propagation in coaxial cables confirms the numerical observations.

Keyword
attenuation measurement, coaxial transmission lines, electromagnetic coupling, finite element methods, FDTD methods, helices, power cable shielding, velocity measurement
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5123 (URN)10.1109/TDEI.2007.344621 (DOI)000245598900019 ()2-s2.0-34147112279 (Scopus ID)
Note
Uppdaterad från submitted till published: 20101012. QC 20101012Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
5. Techniques for Localization of Water-treed Regions along Medium-Voltage Power Cables
Open this publication in new window or tab >>Techniques for Localization of Water-treed Regions along Medium-Voltage Power Cables
2005 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208Article in journal (Other academic) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5124 (URN)
Note
QS 2010 QS 20120319Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
6. Diagnosis of moisture in oil/paper distribution cables-part II: Water penetration in cable insulation-experiment and modeling
Open this publication in new window or tab >>Diagnosis of moisture in oil/paper distribution cables-part II: Water penetration in cable insulation-experiment and modeling
2004 (English)In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 19, no 1, 15-20 p.Article in journal (Refereed) Published
Abstract [en]

Dynamics of water penetration in mass impregnated cable insulation has been studied. For experimental purposes, artificial damage has been inflicted to a 40-cm-long cable sample and water ingress has been continuously monitored by frequency response measurements. A similar experiment has been conducted on 2.8-m-long cable sample, where both frequency response and time-domain reflectometry (TDR) measurements have been performed. After termination of both experiments, actual moisture content has been measured radially and axially. Based on dielectric measurements, a model of water ingress has been developed and diffusion coefficients have been estimated for mass impregnated cable paper.

Keyword
Dielectric response, Karl Fischer titration, Mass impregnated cable, Moisture content, Oil paper insulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5122 (URN)10.1109/TPWRD.2003.820430 (DOI)000187886300003 ()2-s2.0-0348129456 (Scopus ID)
Note
QC 20100908Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
7. Design and Application of a Coupling Connection for High Frequency and High Voltage Diagnostic Measurements on Power Cables
Open this publication in new window or tab >>Design and Application of a Coupling Connection for High Frequency and High Voltage Diagnostic Measurements on Power Cables
2003 (English)In: 18th Nordic Insulation Symposium (NORD-IS), 183-190 p.Article in journal (Refereed) Published
Abstract [en]

Time Domain Reflectometry (TDR) for localisation of power cable discontinuities requiresthe knowledge of the cable wave propagation properties. Additionally, it is beneficialif one can apply high voltage to the cable under investigation for the purpose ofdielectric spectroscopy.This paper presents a design of a high frequency coupling connection that sustains theapplication of high voltages. The extraction of the high frequency cable parameters isthen possible using S-parameter measurements with a Network Analyzer (NA) in thefrequency range 300kHz to 300MHz. The coupling connection is then used in fieldTDR measurements for localisation of cable joints.

Keyword
high frequency parameters, power cables, high voltage dielectric spectroscopy, TDR, localisation of cable joints
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-5126 (URN)
Note
QC 20101012Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2010-10-12Bibliographically approved

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