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Technique Employing Inductive Coupler for Propagation Constant Extraction on Power Cables with Twisted Screen Wires
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2005 (English)In: Proceedings of the Nordic Insulation Symposium, 242-245 p.Article in journal (Refereed) Published
Abstract [en]

This paper investigates a new propagation constant measuring technique in which an inductive coupler allows only the selected part of the cable to be measured. The propagation constants are extracted from frequency and time domain measurements. The extracted propagation constants from measurements with an inductive coupler are compared with the reference propagation constant obtained from direct measurements on the cable. The dependence of the extracted propagation constant accuracy on the measured cable part length is investigated.

Place, publisher, year, edition, pages
Trondheim, Norway, 2005. 242-245 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-9866OAI: oai:DiVA.org:kth-9866DiVA: diva2:134362
Note

QC 20100709

Available from: 2009-01-20 Created: 2009-01-20 Last updated: 2017-04-25Bibliographically approved
In thesis
1. Development of on-line diagnostic methods for medium voltage XLPE power cables
Open this publication in new window or tab >>Development of on-line diagnostic methods for medium voltage XLPE power cables
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

On-line diagnostics of power system components is an important area since it allows the diagnostics to be performed at regular intervals during the normal operation of the components. This combined with reliability centered maintenance could lead to reduced customer outages. In this thesis the on-line diagnostic methods for medium voltage cross-linked polyethylene (XLPE) cables are investigated based on Time Domain Reflectometry (TDR).

Degradation of XLPE insulated power cables by water-trees (WT) is a primary cause of failure of these cables. The detection of WT and information about the severity of the degradation can be obtained with off-line measurements using dielectric spectroscopy.  In many situations only a limited part of the cable may be degraded by the WT. In such a situation a method for localization of this WT section would be desirable.

The developed high frequency measurements superimposed on HV system is presented. It was used to measure the propagation constant of the WT aged cables as a function of the applied HV. This was done in order to study the diagnostic criteria, which could be used for on-line TDR diagnostics of WT aged cables.

A physically based dielectric model of WT was developed in order to explain qualitatively and quantitatively the permittivity and loss of WT at different frequencies and voltages.

The sensors applicable for the on-line TDR were investigated in terms of sensitivity and bandwidth. High frequency models were built and the simulation results in frequency and time domains were verified by measurements.

The developed on-line TDR systems are presented. Their applicability to detect water penetration under the cable sheath and localize the broken screen wires was investigated during the measurements in laboratory environment.

The results of field measurements with on-line TDR are presented. Variations due to load cycling of the cable were observed, where an increase in the cable temperature cause an increase of the pulse propagation velocity in the cable. The temperature dependent wave propagation in the cable is investigated and explained by modeling.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. x, 119 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-9872 (URN)978-91-7415-220-3 (ISBN)
Public defence
2009-02-13, F3, Lindstedsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20100709Available from: 2009-01-29 Created: 2009-01-20 Last updated: 2010-07-12Bibliographically approved
2. On-line time domain reflectometry diagnostics of medium voltage XLPE power cables
Open this publication in new window or tab >>On-line time domain reflectometry diagnostics of medium voltage XLPE power cables
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Degradation of XLPE insulated power cables by water-trees is a primary cause of failure of these cables. The detection of water-trees and information about the severity of the degradation can be obtained with off-line measurement using dielectric spectroscopy. In many situations only a limited part of the cable may be degraded by the water-trees. In such a situation a method for localization of this water-treed section would be desirable. On-voltage Time Domain Reflectometry (TDR) diagnostics proved to be capable of localizing the water-tree degraded sections of the cable. The possibility of using on-voltage TDR as a diagnostic method opens up as a further step for the development of an on-line TDR method where the diagnostics are performed using pre-mounted sensors on the operating power cable. The benefits with such a method are: ability to perform diagnostics without disconnecting the cable from a power grid; the diagnostics performed during a longer period of time could give an extra information; no need for an external high-voltage supply unit.

In this thesis the sensors for the on-line TDR are investigated in terms of sensitivity and bandwidth. High frequency models were built and the simulation results in frequency and time domains were verified by measurements. Results of the on-voltage TDR measurements on the degraded XLPE cables in laboratory as well as on-site are presented.

The on-line TDR system and the results of a four-days on-line measurement sequence are presented. Variations due to load cycling of the cable were observed, where an increase in the cable temperature cause an increase of the pulse propagation velocity in the cable.

A method has been developed for high frequency characterization of power cables with twisted screen wires, where the measurements are performed using inductive strip sensors. This technique allows the high frequency parameters of the selected section of the cable to be extracted. The high frequency parameters are extracted from frequency domain measurements of S-parameters as well as from TDR measurements.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. xi, 69 p.
Series
Trita-EE, ISSN 1653-5146 ; 2006:010
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-3921 (URN)91-7178-327-X (ISBN)
Presentation
2006-04-27, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100709Available from: 2006-04-12 Created: 2006-04-12 Last updated: 2010-11-11Bibliographically approved

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