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  • 1.
    Eriksson, Roland
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Papazyan, Ruslan
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mugala, Gavita
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Localization of insulation degradation in medium voltage distribution cables2006Ingår i: 2006 International Conference on Industrial and Information Systems, Vols 1 and 2, NEW YORK: IEEE , 2006, s. 167-172Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper presents a methodology for successful localization of degraded insulation in medium voltage cables. Extensive work has been performed on development of cable models and characterization of new and degraded cable material to support the diagnostic technique. A non-destructive technique has been developed using differential Time Domain Reflecometry (TDR) measurements. The main application has been localization of water treed sections of XLPE cables where the voltage dependence of the permittivity of water treed insulation has been used as diagnostic criteria.

  • 2.
    Mugala, Gavita
    KTH, Skolan för elektro- och systemteknik (EES).
    High frequency characteristics of medium voltage XLPE power cables2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The response of a cable can be used to analyze the variation of the material characteristics along its length. For diagnosis of possible ageing, it is necessary to know how cable design, material properties and cable insulation ageing affects the wave propagation. A cable model has therefore been worked out based upon the high frequency properties of the cable insulation and conductor systems. The high frequency characteristics of the semi-conducting screens, new and water-tree aged cross-linked polyethylene (XLPE) insulation have been determined by two measuring techniques. Semi-conducting screens have a great influence on the attenuation of cables at high frequencies.

    A dielectric function based on an empirical formula is fitted to the measured characteristics of the semi-conducting screens. The dielectric function is used in the cable model set-up to predict the propagation constant of the cables.

    The high frequency characteristics of the water-tree degraded XLPE insulation obtained from measurements are related to the water content of the water trees of the samples. An effective materials model is developed to estimate the water content of the water trees and the conductivity of the water.

    The propagation constant from the cable model is compared to the propagation constant obtained from measurements made on cables. Using approximate high frequency cable models, the relative contributions of the conductor and insulation systems to the attenuation and phase velocity of the cables are analyzed.

  • 3.
    Mugala, Gavita
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Eriksson, Roland
    KTH, Tidigare Institutioner                               , Elkraftteknik.
    Gäfvert, Uno
    ABB.
    High frequency characterization of the semi-conducting screens of medium voltage XLPE cables2002Ingår i: Electrical Insulation and Dielectric Phenomena, 2002 Annual Report Conference on, Cancun, 2002, s. 887-890Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this study, a high frequency measurement technique to characterize the semi-conducting materials of the medium voltage XLPE cables in the frequency range of 30 kHz to 500 Mhz has been developed. The influence of the experimental set-up and the sample preparation methods are investigated. A dielectric response model is then developed for the semiconducting materials and this is incorporated into a model for the whole cable. The propagation characteristics obtained from the cable model are then compared with those obtained from measurements carried out on the actual XLPE cables.

  • 4.
    Mugala, Gavita
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Eriksson, Roland
    KTH, Tidigare Institutioner, Elkraftteknik.
    Gäfvert, Uno
    ABB.
    Pettersson, Per
    Vattenfall.
    Measurement technique for high frequency characterization of semi-conducting materials in extruded cables2004Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 11, nr 3, s. 471-480Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Knowledge on the dependence of wave propagation characteristics on material properties and cable design is important in establishing diagnostic methods for cable insulation. In this study, a high frequency measurement technique to characterize the semi-conducting screens in medium voltage cross-linked polyethylene (XLPE) cables has been developed. The frequency ranges from 30 kHz to 500 MHz. The influence of the experimental set-up, sample preparation methods, pressure and temperature are investigated. A dielectric function is developed for the semiconducting screens and this is incorporated into a high frequency model for the cable. The propagation characteristics obtained from the high frequency cable model are compared with those obtained from measurements made on the same cables.

  • 5.
    Mugala, Gavita
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Eriksson, Roland
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Pettersson, Per
    Vattenfall.
    Comparing two measurement techniques for high frequency characterization of power cable semi-conducting and insulating materials2006Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 13, nr 4, s. 712-716Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the high frequency characteristics of the materials that make up medium voltage extruded cables is important in establishing diagnostics schemes based on electromagnetic pulse propagation methods. Two measurement techniques have been developed and used to characterize the high frequency material properties of semi-conducting screens and cross linked polyethylene (XLPE) insulation up to 100 MHz. The experimental details, parameter extraction and limitations of the two measurement techniques are presented.

  • 6.
    Mugala, Gavita
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Eriksson, Roland
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Pettersson, Per
    Vattenfall.
    Dependence of XLPE insulated power cable wave propagation characteristics on design parameters2007Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 14, nr 2, s. 393-399Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Propagation losses occur in medium voltage power cables as pulses propagate through them. Since cables have many components, these can make different contributions to the propagation losses. The relative contributions of the conductors, insulation and semi-conducting screens to the propagation characteristics of the cable are analyzed. The propagation characteristics of the cables are studied by a developed "approximate" model providing analytical expressions that can quantify the contributions to the losses by the different parts of the conductor and dielectric system. The model is compared with an "exact" model and is tested on four cables. © 2007 IEEE.

  • 7.
    Mugala, Gavita
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Eriksson, Roland
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Pettersson, Per
    Vattenfall.
    High frequency characteristics of water-tree degraded XLPE insulation in power cables2007Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 14, nr 5, s. 1271-1277Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The high frequency characteristics, the complex permittivity in particular, of water-tree degraded XLPE insulation in power cables are determined using a two port measurement method. The insulation samples are obtained from both laboratory made samples and those from ex-service cables. The electrical measurements are related to the water tree content of the samples which is estimated by an optical method. An effective materials model is derived to help understand the observed characteristics. From the model it is possible to estimate the water content of the water tree and the conductivity of the water. There is a considerable difference in the water tree characteristics between laboratory and service aged cables. The conductivity of the water in the water trees of service aged cables is much higher than that found in laboratory aged samples.

  • 8.
    Mugala, Gavita
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Papazyan, Ruslan
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Nakov, P.
    High frequency characterization of medium voltage cables using time domain Reflectometry techniques2001Ingår i: 17th Nordic Insulation Symposium(NORD-IS 01), Stockholm, Sweden, 2001, s. 211-218Konferensbidrag (Refereegranskat)
  • 9.
    Mugala, Gavita
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Pettesson, Per
    Vattenfall.
    Eriksson, Roland
    KTH, Tidigare Institutioner                               , Elkraftteknik.
    Development of a measurement technique for high frequency characterization of insulation materials2004Ingår i: 2004 ANNUAL REPORT CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA, NEW YORK: IEEE , 2004, s. 206-209Konferensbidrag (Refereegranskat)
    Abstract [en]

    A technique to measure the high frequency characteristics of insulation materials has been developed. Using this technique, high frequency characteristics of known insulation materials have been obtained to check its accuracy. The test cell, measurement technique and the extraction of the relevant parameters from the measurements are discussed.

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