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  • 1.
    Abid, Fahim
    et al.
    KTH.
    Ghorbani, Hossein
    Pourrahimi, Amir Masoud
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Edin, Hans Ezz
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Differences in morphology and polarization properties of heat-treated XLPE and LDPE insulation2016Inngår i: 2016 IEEE CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA (IEEE CEIDP), IEEE conference proceedings, 2016, s. 113-116Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cross-linked polyethylene (XLPE) is the most commonly used insulating material for extruded high voltage cable applications. Degassing is a heat-treatment process that is performed to remove methane from XLPE insulation which is formed during the crosslinking reactions as a by-product. Apart from removing methane, heat-treatment influences the electrical properties through changing the morphology due to annealing and also removal of polar crosslinking by-products. Scanning electron microscopy (SEM) is generally used to observe the changes in crystalline structure of the polymer. Frequency domain spectroscopy (FDS) is widely used to study polarization properties of dielectric materials. In this study these two methods are used for a comparative analysis of XLPE and LDPE subjected to different heat-treatment time, with or without a diffusion barrier. Electrical measurements are performed at room temperature. From the SEM imaging conducted after permanganate acid etching, formation of spherulites due to heat-treatment is not obvious in neither LDPE nor in XLPE. However, distinctions between LDPE and XLPE in SEM micrographs are evident. From studies with dielectric polarization spectroscopy, it is found that the LDPE samples are less sensitive to heat-treatment in comparison to the XLPE samples while dissipation factor of XLPE samples are influenced by the choice of pressing film used during sample preparation.

  • 2.
    Doddapaneni, Venkatesh
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bissal, Ara
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Magnusson, Jesper
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Gati, Rudolf
    EFFECT OF POLYMER BASED NANOCOMPOSITES ON THE ELECTRICAL ARCS IN AIR2015Inngår i: 2015 42ND IEEE INTERNATIONAL CONFERENCE ON PLASMA SCIENCES (ICOPS), ISSN 0730-9244Artikkel i tidsskrift (Annet vitenskapelig)
  • 3.
    Doddapaneni, Venkatesh
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Magnusson, Jesper
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bissai, A.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik.
    Gati, R.
    Spectroscopic investigations of the ablated species from the polymers exposed to electric arcs in air2015Inngår i: 2015 3rd International Conference on Electric Power Equipment - Switching Technology, ICEPE-ST 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, s. 337-340Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Polymeric walls have been widely used in the last decades to improve the arc interruption process in electrical switching applications. This improvement is achieved by the evaporation (ablation) of the polymeric walls due to the highly energetic radiation generated by the electrical arcs. This experimental study deals with polymeric walls that are exposed to the electrical arcs generated between a 5 mm air gap with prospective current of 1.4 kA. In this paper, two different techniques are discussed aiming at the identification of the dominant ablated species produced during the arc interruption process, namely Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis coupled with Fourier transform infrared analysis of evolved gases (EGA). In addition, the morphological and chemical changes on the surface of the exposed polymeric walls are analyzed by microscopical techniques.

  • 4.
    Doddapaneni, Venkatesh
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Zhao, Yichen
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Ye, Fei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Gati, R.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Toprak, Muhammet S.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Funktionella material, FNM.
    Improving Uv Radiation Absorption by Copper Oxide NPs/PMMA Nanocomposites for Electrical Switching Applications2015Inngår i: Powder metallurgy and metal ceramics, ISSN 1068-1302, E-ISSN 1573-9066, Vol. 54, nr 7-8, s. 397-401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanocomposites based on the radiation absorbing polymer (PNCs) are of interest for a variety of applications including circuit breakers, UV-shielding windows, contact lenses, and glasses among others. Such PNCs can be made by incorporating suitable radiation absorbing nanoparticles into a polymeric matrix by in situ polymerization. In this study, spherical nanoparticles (5-6 nm) of oleic acid (OA) surface modified cupric oxide (CuO) are synthesized and used to improve the ultra-violet (UV) radiation absorption property of a polymer matrix, i.e., polymethylmethacrylate (PMMA). The synthesis of spherical CuO nanoparticles, surface modification using OA, dispersion of CuO nanoparticles with different concentrations in PMMA, and UV radiation absorption property of the resultant PNC are investigated. Two different PNCs are produced using OA modified CuO nanoparticles with different concentrations. As synthesized CuO nanoparticles and OA modified CuO nanoparticles are examined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The UV absorption edges are evaluated from the UV-Vis absorption spectra by using UV-Visible absorption spectroscopy. The results show that the UV radiation absorption of the PNC with higher concentration of CuO nanoparticles is improved compared with PMMA and the absorption edge moved towards longer wavelengths i.e., from 271 to 281 nm. These PNCs are successful in arc interruption process by absorbing a broad range of radiation emitted from high-energy copper arcs produced in the circuit breakers.

  • 5.
    Dubickas, Valentinas
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Edin, Hans
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Couplers for on-line Time Domain Reflectometry diagnostics of power cables2004Inngår i: 2004 ANNUAL REPORT CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA, 2004, s. 210-214Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper investigates three types ofcouplers for sending and receiving a Time DomainReflectometry (TDR) signal to and from a cable on-line.Transfer functions of the couplers were estimated andlumped element models were built. The couplers wereplaced on a power cable with High Voltage (HV)terminations. Measurements were performed at a HVsimulating realistic conditions. In this cable weinvestigated voltage pulse injection, propagation, anddetection for different coupler topologies and HVterminations.

  • 6.
    Dubickas, Valentinas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dielectric model of water trees in an XLPE cable2008Inngår i: International Symposium on Electrical Insulating Materials (ISEIM 08), Yokkaichi, Japan, 2008, s. 448-451Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper a water-tree degraded insulation is modeled as a matrix composed of cubic cells. In the model there are three types of cells: pure XLPE, XLPE with water inclusion and the XLPE cell with a cylindrical water channel. Voltage dependant dielectric properties of the water-trees are modeled by an elongation of the inclusions and appearance of the conducting channels caused by the Maxwell stress. Afterwards the modeled effective permittivity of the insulation matrix is compared with the dielectric spectroscopy measurements of a field aged XLPE cable.

  • 7.
    Dubickas, Valentinas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    High-Frequency Model of the Rogowski Coil With a Small Number of Turns2007Inngår i: IEEE Transactions on Instrumentation and Measurements, ISSN 0018-9456, Vol. 56, nr 6, s. 2284-2288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the Rogowski coil is modeled as adistributed-element transmission line. The elements in the distributedtransmission line are modeled using physically basedequations. It allows self and transfer impedances of the Rogowskicoil to be modeled using the physical dimensions and the materialproperties of the coil. The models of the impedances were verifiedby measurements in the frequency domain on three Rogowskicoils. The coils mounted on the power cable were modeled andsimulated in the time domain and afterward compared with themeasurements.

  • 8.
    Dubickas, Valentinas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On-line time domain reflectometry measurements of temperature variations of an XLPE power cable2006Inngår i: 2006 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Kansas City, Missouri, USA, 2006, s. 47-50Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper an on-line time domainreflectometry system and a four-days measurementssequence are presented. Detected pulse velocityvariations are attributed to temperature variations of thecable caused by a load cycling. The changes in the pulsevelocity are verified by propagation constantmeasurements of a power cable at differenttemperatures in 300 kHz - 500 MHz frequency range.Also an influence of temperature dependentsemiconducting screens and XLPE insulation to thechanges in the cable's capacitance is investigated.

  • 9.
    Dubickas, Valentinas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Technique Employing Inductive Coupler for Propagation Constant Extraction on Power Cables with Twisted Screen Wires2005Inngår i: Proceedings of the Nordic Insulation Symposium, s. 242-245Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 10.
    Dubickas, Valentinas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Temperature influence on wave propagation in XLPE power cables: on-line and laboratory measurements2009Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    This paper investigates the influence of temperature on the wave propagation in medium voltage XLPE power cables. During an on-line time domain reflectometry measurements a periodicity of the pulse velocity was observed. These variations are attributed to the temperature changes of the cable caused by the load cycling. The results of the on-line measurements were verified by laboratory measurements of the propagation constant as a function of temperature in the 0.3 – 500 MHz frequency range. It is shown that the changes in the propagation constant are mainly caused by the temperature dependent permittivities of the semiconducting shields and the XLPE insulation.

  • 11.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Partial Discharges Studied with Variable Frequency of the Applied Voltage2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis concerns partial discharge (PD) diagnostics withvariable frequency of applied voltage in the frequency range 1mHz - 400 Hz. The exploration of a new type of spectroscopythat combines partial discharge analysis and dielectricresponse is demonstrated. A question addressed is if and howthe PD activity varies with the frequency of the appliedvoltage. The nature of an existing frequency dependence couldbe useful in the classification of different defects and tojudge the degree of progressive ageing.

    A Variable-Frequency Phase Resolved Partial DischargeAnalysis (VF-PRPDA) technique is developed for the appliedvoltage frequency range 1 mHz - 400 Hz. The VF-PRPDA techniqueis combined with a system for high voltage dielectricspectroscopy that allows simultaneous measurements. TheVF-PRPDA technique is used for studying the frequencydependence of PD. The PD activity is for example measured byintegrated measures like total charge per cycle and totalnumber of discharges per cycle. Statistical measures like mean,standard deviation, skewness, kurtosis etc. are applied tomeasure the frequency dependence of the phasedistributions.

    High voltage dielectric spectroscopy is supplemented withharmonic analysis for studying non-linear dielectric responsecurrents.

    The VF-PRPDA technique is demonstrated on defined objectslike point-plane gaps and artificial voids, but also on aninsulated stator bar and a paper insulated cable. Surfacedischarges on insulating surfaces are studied in an environmentwith a controlled relative humidity and temperature. Theadsorption of moisture on the insulating surface alters thesurface conductivity of the surface and the frequencydependence of the PD activity.

    The influence of temperature upon the PD activity is studiedfor a oil paper insulated cable.

    The results of the measurements show that the partialdischarge activity in general is frequency dependent over thefrequency range 1 mHz - 400 Hz. The reasons behind thefrequency dependence are linked to surface- and bulk-conducting mechanisms, frequency dependent field distributionsand statistical effects of the supply of start electrons.

    An algorithm is developed that relates the phase resolved PDcurrent measured with the PRPDA technique to the non-linearcurrent measured with dielectric spectroscopy. The algorithm isexperimentally verified by simultaneous measurements of PRPDAand dielectric spectroscopy on defined objects. The resultsexplain the contribution of PD to the apparent capacitance andloss. Moreover, the harmonics of the fundamental currentcomponent yield information about, for example, polaritydependent discharge sources.

    Keywords:diagnostic methods, partial discharges, phaseresolved, variable frequency, dielectric spectroscopy,dielectric response, harmonics, insulation

  • 12.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    the influence of dielectric polarisation on the measured pd charge in a two-layer dielectric system1999Inngår i: Proceedings of Nordic Insulation Symposium, 1999, s. 433-441Konferansepaper (Annet vitenskapelig)
  • 13.
    Edin, Hans
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Forssén, Cecilia
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Variable frequency partial discharge analysis of in-service aged machine insulation2003Inngår i: Proceedings Nordic Insulation Symposium, 2003, s. 29-35Konferansepaper (Fagfellevurdert)
  • 14.
    Edin, Hans
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Gäfvert, Uno
    harmonic content in partial discharge current measured with dielectric spectroscopy1998Inngår i: Annual report. 1998, 1998Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Phase resolved partial discharge analysis and dielectricspcctroscopy measurements have been performed at50Hz and variable voltage on two artificial defects thathave different average charge phase distributions. Influenceof partial discharges on permittivity and loss-factoris dcduced to the phase position of the partial dischargeactivity. Symmetry properties between positive andnegative charge distributions have been related to theharmonic content of the partial discharge current.

  • 15.
    Edin, Hans
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Gäfvert, Uno
    Simultaneous measurement of phase resolved partial discharges and dielectric spectroscopyInngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135Artikkel i tidsskrift (Annet vitenskapelig)
  • 16.
    Edin, Hans
    et al.
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Jayaram, Shesha
    KTH, Tidigare Institutioner, Elektrotekniska system.
    Gäfvert, Uno
    influence of relative humidity on surface discharge over the frequency range 01 hz to 100 hzInngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135Artikkel i tidsskrift (Annet vitenskapelig)
  • 17.
    Ekelund, Maria
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gedde, Ulf W
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Long-term performance of poly(vinyl chloride) cables. Part 1: Mechanical and electrical performances2007Inngår i: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 92, nr 4, s. 617-629Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cables insulated with plasticized poly(vinyl chloride) were aged in air at temperatures between 80 degrees C and 180 degrees C and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break (HELB) to the mechanical properties and to establish a lifetime criterion. The mechanical data taken at room temperature after ageing could be superimposed with regard to ageing time and temperature. The ageing-temperature shift factor showed an Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter modulus and Young's modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration which was confirmed by IR spectroscopy and DSC. The core insulation showed smaller changes in these mechanical parameters; the loss of plasticizer by migration was greatly retarded by the closed environment, according to data obtained by IR spectroscopy and DSC, and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). A comparison of data obtained from this study and data from other studies indicates that extrapolation of data for the jacketing insulation can be performed according to the Arrhenius equation even down to service temperatures (20-50 degrees C). The low-temperature deterioration of the jacketing is, according to this scheme, dominated by loss of plasticizer by migration.

  • 18.
    Engdahl, Göran
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Blomberg, Lars
    Brunsell, Per
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Rosander, Staffan
    Electrotechnical modelling2011Annet (Annet vitenskapelig)
  • 19.
    Engdahl, Göran
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Eriksson, Roland
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Hörnfeldt, Sven
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Schönborg, Niclas
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Electrotechnical Modelling and Design2011Annet (Annet vitenskapelig)
  • 20.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Field model of partial discharges at variable frequency of the applied voltage2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper the PD frequency dependence of acylindrical cavity in a delaminated insulation issimulated using a field model. It is shown how thestatistical time lag influences the PD frequencydependence. The technique of Variable FrequencyPhase Resolved Partial Discharge Analysis (VFPRPDA)is applied to a test object and measurementdata is compared with the results of the simulations.

  • 21.
    Forssén, Cecilia
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Influence of cavity size and cavity location on partial discharge frequency dependence2004Inngår i: 2004 ANNUAL REPORT CONFERENCE ON ELECTRICAL INSULATION AND DIELECTRIC PHENOMENA, New York: IEEE , 2004, s. 438-441Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Variable frequency phase resolved partial discharge analysis (VF-PRPDA) is a partial discharge measurement technique where the frequency of the applied voltage is variable. In this paper, the VF-PRPDA technique is applied to a test object containing a cylindrical cavity in an otherwise homogeneous insulation of polycarbonate. The frequency is varied in the range 10 mHz-100 Hz. It is shown how the frequency dependence of PD is influenced by the cavity diameter and the cavity location in relation to the electrodes. The PD frequency dependence is also numerically modeled for an isolated cylindrical cavity with diameter 1.5 mm using a field model.

  • 22.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Measured Applied Frequency Dependence of Partial Discharges in Disc-Shaped Cavities2007Inngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135Artikkel i tidsskrift (Annet vitenskapelig)
  • 23.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Measured Partial Discharge Inception Voltage for a Cavity at Different Applied Frequencies2007Inngår i: Nordic Insulation Symposium (Nord-IS 07), 2007, s. 59-62Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Partial discharges (PD) can be measured at variable frequency of the applied voltage. The interpretation of such measurements requires a physical understanding of the observed PD frequency dependence. This paper studies the influence of the applied frequency on the partial discharge inception voltage (PDIV). The PDIV is measured for insulated disc-shaped cavities at applied frequency in the range 0.1 to 100 Hz. It is found that the PDIV increases with increasing applied frequency, probably as an effect of the statistical time lag. In addition, the measured PDIV is lower than that predicted by Paschens’s law. The effect of preexcitation on PDIV is also studied. A period without voltage supply prior to each PDIV measurement is  seen to cause a faster increase in the PDIV with frequency.

  • 24.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Modeling of a discharging cavity in a dielectric material exposed to high electric fields2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Partial discharges are localized electric discharges that do not bridge the electrodes. For high voltage components measurements of partial discharges arecommonly used to diagnose the condition of the insulationsystem. Traditionally partial discharges are measuredat a single frequency of the applied voltage. Howeverthe rather newly developed technique of VariableFrequency Phase Resolved Partial Discharge Analysis(VF-PRPDA) makes it possible to measure partial dischargesat variable frequency of the applied voltage. Thebenefit of varying the frequency is that more informationabout the state of the insulation system is obtainedthan from measurements at a single frequency. This paperpresents a model of partial discharges in a cavity atvariable applied frequency. The aim of the model is to increasethe physical understanding of how the frequencyof the applied voltage affects the partial discharges in thecavity. This paper studies the influence from the statisticaltime lag on the frequency dependent discharge sequenceand results from simulations are compared withmeasurement data. The model is a 2D time dependent FEMLAB model in PDE mode which is handled from aMATLAB script.

  • 25.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Modeling Partial Discharges in a Cavity at Different Applied Frequencies2007Inngår i: Annual Conference on Electrical Insulation and Dielectric Phenomena: Vancouver, CANADA, OCT 14-17, 2007, 2007, s. 132-135Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A model of partial discharges (PD) in an insulated disc-shaped cavity is presented. The flat cavity walls are covered with copper foil and each PD is assumed to affect the whole cavity. The discharge process in the cavity is simulated dynamically and the model is charge consistent. The model is used to simulate the sequence of PDs in the cavity at two different applied frequencies: 0.02 Hz and 100 Hz. The simulation results are compared with measurements and good agreement is found. As the applied frequency is increased from 0.02 Hz to 100 Hz, the mean apparent charge increases and the number of PDs per cycle of the applied voltage reduces. This is interpreted as an effect of the statistical time lag of PD.

  • 26.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Partial Discharges in a Cavity at Variable Applied Frequency: Part 1: Measurements2008Inngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, nr 6, s. 1601-1609Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.

  • 27.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Partial discharges in a cavity at variable applied frequency part 2: Measurements and modeling2008Inngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, nr 6, s. 1610-1616Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    In this paper partial discharges (PD) in a disc-shaped cavity are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The measured PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, changed with the varying frequency. A charge consistent model is presented and used to dynamically simulate the sequence of PDs in the cavity. The simulation results show that the properties of the cavity surface, mainly the surface conductivity and the surface emission of electrons, change with the varying applied frequency. This is interpreted as an effect of the difference in time between consecutive PDs at different applied frequencies. This is the second of two papers addressing the frequency dependence of PD in a cavity. The first paper described how the PD frequency dependence changes with the applied voltage amplitude, the cavity size and the cavity location.

  • 28.
    Forssén, Cecilia
    et al.
    KTH, Skolan för elektro- och systemteknik (EES).
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES).
    Partial discharges in cylindrical cavities at variable frequency of the applied voltageArtikkel i tidsskrift (Annet vitenskapelig)
  • 29.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Corona in oil as a function of geometry, temperature and humidity2010Inngår i: 2010 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE , 2010, s. 5724061-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Corona discharge in oil is one of a number of important defects that may exist in a power transformer. This paper investigates the corona in oil from a needle-plane geometry. Different aspect ratios of the geometry are investigated as well as the temperature dependence from 25 to 100 °C. The corona discharges are measured both in time domain with oscilloscopes and as phase resolved patterns. By using COMSOL, a simple simulation of the electric field in the needle-plane geometry is computed. Simulation of electrical field around the needle tip for different needle length and distance from the needle tip to plane is performed. An amplification factor of electrical field around the tip, according to these parameters is developed. By considering corona inception voltage as a function of electrical field around the tip, by using the same geometries for simulation and measurement, inception field for corona in oil as a function of electrical field is calculated. The results show the dependency of corona inception voltage, discharge magnitude and repetition rate on the geometrical parameters, temperature and humidity.

  • 30.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Partial Discharge Due to Bubbles in Oil2011Konferansepaper (Fagfellevurdert)
  • 31.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicus
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Oil Aging due to Partial Discharge Activity2013Inngår i: Proceedings of the23rd NORDIC INSULATIONSYMPOSIUM, NORD-IS &Akademika Publishing , 2013, s. 85-88Konferansepaper (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Oil is the main insulation in power transformers and over long time of ageing its insulation properties can change. In this paper ageing of oil due to the exposure to electric discharges was investigated. The effect of high energy discharges (complete arc) and low energy discharges (partial discharges) on oil properties such as breakdown strength and oil conductivity was investigated. An experimental setup consisting of two spherical electrodes was designed. The adjustable distance between the two electrodes made it possible to have PD with different magnitude. The oil conductivity and breakdown strength was measured for three sets of experiments. The first group of experiments was performed on new oil in order to have a reference for comparison. In the second group of experiments the new oil samples was exposed to 1000 and 3000 lightning impulses. In the third group of experiments new oil samples was exposed to partial discharge for different duration of time. Oil conductivity and breakdown strength of these aged samples were compared with new oil. The results show that after exposure to lightning impulse oil conductivity increases and breakdown strength decreases, However PD activity for short time does not change the oil conductivity but it reduces the breakdown strength.

  • 32.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Xiaolei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Partial Discharge Characteristics Due to Air and Water Vapor Bubbles in Oil2011Konferansepaper (Annet (populærvitenskap, debatt, mm))
  • 33.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    Elektroteknisk teori och konstruktion, Electromagnetic Engineering.
    Wang, Xiaolei
    Elektroteknisk teori och konstruktion, Electromagnetic Engineering.
    Kiiza, Respicus
    Elektroteknisk teori och konstruktion, Electromagnetic Engineering.
    Nikjoo, Oya
    Elektroteknisk teori och konstruktion, Electromagnetic Engineering.
    Aging of oil impregnated paper due to Pd activity2013Konferansepaper (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Air filled cavity may appear inside solid insulation either due to bad manufacturing or as a result of insulation ageing. A cavity is a weak point in insulation and if the electric stress is high enough; partial discharge can be initiated inside the cavity. In this paper changing of PD parameters (number of PD, maximum magnitude of PD and average magnitude of PD) was investigated over time on oil impregnated paper with an artificial cavity in between the sheets of paper. PD parameters were recorded from the inception of PD until final puncture breakdown occurs in the sample. Experiment was performed on sample with different thickness. Specific pattern on changing of PD number and maximum magnitude of PD was observed for most of the experiments. The pattern includes three stages, big discharges appear at inception of PD and over a very short time they disappear. At stage two, the number and magnitude of PD increase rapidly from small values until they reach to a maximum value. At stage three, the number and magnitude of PD decreases and reach to a constant value. The PD parameter keep constant until the time that final breakdown occurs. The dielectric spectroscopy performed on the sample before and after exposure to PD shows that PD activity causes a permanent shift on ε" which can be explained by PD by-products.

  • 34.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Effect of Partial Discharges on Thermal Breakdown of Oil Impregnated Paper2015Inngår i: IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, ISSN 1931-4973, E-ISSN 1931-4981, Vol. 10, s. S14-S18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate the effect of partial discharges (PDs) on the thermal breakdown voltage of oil-impregnated paper (OIP). A disk-shaped cavity in a stack of paper sheets formed the PD source. The paper sample was exposed to PDs for 18 h. Dielectric spectroscopy measurements were performed on the samples before and after exposure to PD activity. The dielectric spectroscopy results showed a big change in the real and imaginary part of the permittivity. These results were used to calculate the activation energy and heat losses inside the insulation. In order to investigate the possibility of thermal breakdown in the system, the OIP system was simulated by using the FEM software COMSOL Multiphysics. The heat produced by PD pulses and dielectric losses was considered in the simulation. The results show that for the OIP insulation, PD activity can reduce the thermal breakdown voltage by a factor up to 4 times.

  • 35.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Xiaolei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Tenbohlen, Stefan
    Effect of Partial Discharges on Thermal Breakdown of Oil Impregnated Paper2014Inngår i: Conference Proceedings of ISEIM 2014, IEEE conference proceedings, 2014, s. -199Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper the effect of partial discharges on the thermal breakdown voltage of oil-impregnated paper is investigated. A disc shaped cavity in a stack of paper sheets formed a PD source. The paper sample was exposed to partial discharges for 18 hours. Dielectric spectroscopy measurements were performed on the samples before and after exposure to PD activity. The dielectric spectroscopy results showed a big change in the real and imaginary part of the permittivity. These results were used to calculate activation energy and heat losses inside the insulation. In order to investigate the possibility of thermal breakdown in the system, the oil-impregnated paper system was simulated by using the FEM software Comsol Multiphysics. The heat produced by PD pulses and dielectric losses was considered in the simulation. The results show that for the oil-impregnated paper insulation, the PD activity can reduce the thermal breakdown voltage by a factor up to 4 times.

  • 36.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Xiaolei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Partial discharge patterns in a cavity embedded in oil-impregnated papers: Part 2: Effect of thermalageingArtikkel i tidsskrift (Annet vitenskapelig)
  • 37.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Xiaolei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Nikjoo, Roya
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Effect of temperature on surface discharge in oil2012Inngår i: 2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE , 2012, s. 96-99Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper surface discharge along the oil-pressboard interface was investigated. Surface discharges were measured both in time domain by means of an oscilloscope and as phase resolve patterns. The effect of temperature from 20°C to 90°C on surface discharge inception, extinction and surface flashover voltage were investigated. Trend of number and maximum magnitude of PD was compared for 20°C and 90°C over time. The effect of voltage rise and surface flashover on number and maximum magnitude of PD were investigated. The results show that PD inception voltage is lower for higher temperature but surface flashover voltage is higher for higher temperature. However for 90°C the final damage due to surface discharge is much severe compared to 20°C.

  • 38.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Janus, Patrick
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wang, Xiaolei
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    DIT Dar Es Salaam Institute of Technology, Tanzania .
    Partial Discharges in a Cavity Embedded in Oil-Impregnated Paper: Effect of Electrical and Thermal Aging2015Inngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 22, nr 2, s. 1071-1079, artikkel-id 7076808Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, the rapid aging due to Partial Discharge (PD) activity was investigated in unaged and thermally aged oil-impregnated paper with a disk-shaped cavity between the sheets of paper. The PD inception voltage and the voltage for instantaneous breakdown were measured, and the time to breakdown was measured by applying voltages less than the instantaneous breakdown voltage. A comparison between time to breakdown of unaged and thermally aged paper shows no significant difference between thermally aged and unaged paper at sustaining PD activity. The time to breakdown as a function of applied electric field was plotted and compared for both cases showing points scattered around a line in log-log scale. Changes of the PD parameters, such as PD magnitude and PD repetition rate were analyzed from the beginning of PD activity up to the moment of breakdown. The results show that the number and magnitude of PD increase at the beginning of aging until they reach to a maximum value, then both quantities decrease slowly over time until the final puncture breakdown occurs. The results emphasize the importance of PD monitoring on real equipment with oil-impregnated paper as insulation system, such as power transformers, since a focus on the number and magnitude of PD at just the present time may mislead the interpretation. Dielectric spectroscopy measurements performed on unaged and thermally aged paper showed an increasing trend of epsilon '' after the sheets of paper were exposed to thermal aging for longer time. Dielectric spectroscopy measurements performed on samples before and after exposure to PD activity showed a big change of epsilon '', This change can be attributed to byproducts and ions produced by PD activity.

  • 39.
    Ghaffarian Niasar, Mohamad
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kiiza, Respicius Clemence
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dielectric Frequency Response of Oil-impregnated paper: the Effect of Partial Discharges Compared to other InfluencesManuskript (preprint) (Annet vitenskapelig)
  • 40. Ghorbani, H.
    et al.
    Christen, T.
    Edin, Hans Ezz
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Role of thermal and electrical relaxations for the long-term conduction current in polyethylene2016Inngår i: Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 1106-1109Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The characterization of the electrical conduction behavior of polymeric insulating material is a challenging task. Typical reasons are the underlying complexity of the physical processes, the smallness of the current, and the long relaxation times. Moreover, even if the external conditions like applied voltage and temperature are time-constant, often a steady-state direct current (DC) is not established during the measurement time, which may last up from hours to months. This work reports on DC current measurements on 1 mm thick press molded LDPE and XLPE samples. The results show that the conductance is slowly decaying sub-linearly with time, I∼tp, with 0 <-p < 1, p often around-0.5. In certain cases an intermediate current maximum is observed. There is strong indication that the decay of the effective conductivity is due a thermal process rather than to an electrical process.

  • 41. Ghorbani, H.
    et al.
    Saltzer, M.
    Abid, Fahim
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Effect of heat-treatment and sample preparation on physical properties of XLPE DC cable insulation material2016Inngår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 23, nr 5, s. 2508-2516, artikkel-id 7736807Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Power cables with extruded crosslinked polyethylene (XLPE) insulation are used in HVAC and HVDC applications. These cables usually go through a degassing process to remove the methane formed in XLPE during the cross-linking reactions. In case of HVDC cables, the general belief is that the polar peroxide decomposition products (PDP) content significantly influences the conduction and space charge behavior of XLPE. This belief is mainly based on the results of experiments made on thin XLPE samples with different heat-treatments; but since heat-treatment also influences the morphology of the polymer, it is necessary to consider this effect as well. It is common to use polyethylene terephthalate (PET) film as a protective layer during sample press molding. Studies on the influence of the pressing film on the electrical properties of the sample are rare. In this work, the results of a series of experiments performed on 0.5 mm thick XLPE plaque samples in reference to additive free LDPE samples with different heat-treatment times are presented. Beside the PDP content, the morphology, DC conductivity and polarization properties are studied and analyzed. It was found that the pressing film used during sample preparation has a significant effect on the results and if not corrected, it may lead to wrong conclusions about the influence of the PDP content. Eliminating the effect of the pressing film, no clear correlation between the DC conductivity, dielectric loss and the PDP content was observed. The relation between the PDP content and DC conductivity is not found to be obvious, hence this correlation may need to be further evaluated.

  • 42.
    Ghorbani, Hossein
    et al.
    ABB AB, High Voltage Cables, Karlskrona, Sweden.
    Hoq, Tanbhir
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Effect of heat treatment on morphology and dielectric properties of PE cable insulation material2015Inngår i: Nordic Inslu. Symp., 2015Konferansepaper (Fagfellevurdert)
  • 43.
    Ghorbani, Hossein
    et al.
    ABB AB, High Voltage Cables, Karlskrona, Sweden.
    Saltzer, Markus
    ABB AB, High Voltage Cables, Karlskrona, Sweden.
    Abid, Fahim
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Heat-treatment and physical properties of high voltage DC XLPE cable insulation materialManuskript (preprint) (Annet vitenskapelig)
  • 44. Giddens, J
    et al.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Gäfvert, Uno
    Measuring system for phase resolved partial discharge detection at low frequencies1999Inngår i: 11th International symposium on high voltage engineering, 1999, s. 5.228-5.231Konferansepaper (Annet vitenskapelig)
  • 45. Giddens, J
    et al.
    Edin, Hans
    Gäfvert, Uno
    statistical analysis for phase resolved partial discharge detection at low frequencies1999Inngår i: Proceedings of Nordic Insulation Symposium, 1999, s. 141-148Konferansepaper (Annet vitenskapelig)
  • 46. Giddens, J
    et al.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Gäfvert, Uno
    statistical analysis of partial discharges for the frequency range 1 Hz to 400 HZ1999Inngår i: : Proceedings of Nordic Insulation Symposium, 1999, s. 141-148Konferansepaper (Annet vitenskapelig)
  • 47.
    Gäfvert, Uno
    et al.
    ABB Corporate Research.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Forssén, Cecilia
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Modelling of Partial Discharge Spectra Measured with Variable Applied Frequency2003Inngår i: Proceedings of the 7th international conference on properties and applications of dielectric materials, 2003, s. 839-842Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Variable Frequency Phase Resolved Partial Discharge Analysis (VF-PRPDA) is a newly developed method for partial discharge measurements. In this method the frequency of the applied voltage is variable and not fixed at the power frequency as in the standard PRPDA implementation. In this paper, simulations illuminate the frequency dependence of PD of a discharging cavity embedded in an otherwise homogeneous insulation. It is shown how the frequency dependence is influenced by the conductivity of the bulk insulation, the surface conductivity of the cavity walls and the statistical time lag. The results of simulations are compared with result of measurements on an asphalt-mica insulated machine stator bar.

  • 48. Holbøll, Joachim
    et al.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    PD Detection vs. Loss Measurements at High Voltages with variable power frequencies1997Inngår i: International Symposium on High Voltage Engineering, 1997, s. 4.421-4.425Konferansepaper (Annet vitenskapelig)
  • 49. Holbøll, Joachim
    et al.
    Edin, Hans
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Gäfvert, Uno
    Time domain PD-detection vs. dielectric spectroscopy1997Inngår i: IEEE 1997 Annual Report: IEEE conference proceedings, 1997, s. 498-503Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A theoretically developed relationship between partial discharges and the response from a system for dielectric spectroscopy was experimentally confirmed. The losses caused by the discharges were highest at test voltages with low frequencies. At 0.1 Hz, tanδ tip-up at discharge inception was very difficult to observe. A very clear tip-up could be seen by detection of the third harmonic in the current through the test object. This is much more sensitive to the detection of internal partial discharges than traditional loss measurements, in particular when using low frequency test voltages

  • 50.
    Jonsson, B. Lars G.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Venkatesulu, Bandapalle
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Observations on the Resistive Losses and the Electrostatic Field Distribution in anInsulating Nanocomposite2011Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It has been reported that adding insulating nanoparticles to an epoxy like polymers increases its dielectric breakdown strength. Thermal runaway can act as one of several precursors to the electrical breakdown process, and resistive losses can be an underlying cause of the temperature increase. In this paper, to examine the influence of nanoparticles on the breakdown strength, the magnitude of the electric field distribution and its corresponding resistive losses around insulating Al2O3-nanoparticles has been determined for linear and non-linear epoxy polymer media w.r.t. filling degree of particles. The dc-E-field distribution has been ascertained using both analytical and numerical methods. It was observed that nanoparticle addition to a polymer creates both "no heating" regions and "significant heating" regions in the close vicinity of the interface.

123 1 - 50 of 110
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