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Modeling of a discharging cavity in a dielectric material exposed to high electric fields
KTH, School of Electrical Engineering (EES).
KTH, School of Electrical Engineering (EES).
2005 (English)Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
2005.
Keyword [en]
Insulation diagnostics, partial discharges, variable applied frequency
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-8508OAI: oai:DiVA.org:kth-8508DiVA: diva2:13852
Conference
FEMLAB Conference, Stockholm, Sweden, October 2005
Note
QC 20101129Available from: 2005-11-08 Created: 2005-11-08 Last updated: 2010-11-29Bibliographically approved
In thesis
1. Partial discharges in cylindrical cavities at variable frequency of the applied voltage
Open this publication in new window or tab >>Partial discharges in cylindrical cavities at variable frequency of the applied voltage
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Measurements of partial discharges are commonly used to diagnose the insulation system in high voltage components. Traditionally a single xed frequency of the applied voltage is used for such measurements as in the Phase Resolved Partial Discharge Analysis (PRPDA) technique. With the Variable Frequency Phase Resolved Partial Discharge Analysis (VF-PRPDA) technique the frequency of the applied voltage is instead variable. This technique provides more information about the condition of the insulation than the PRPDA technique. To extract the extra information a physical understanding of the frequency dependence of partial discharges is necessary.

In this thesis partial discharges in cylindrical cavities in polycarbonate are measured using the VF-PRPDA technique in the frequency range 10 mHz { 100 Hz. It is studied how the cavity diameter and height inuence the frequency dependence of partial discharges. Insulated cavities are compared with cavities bounded by an electrode. It is shown that from measurements at variable applied frequency it is possible to distinguish between cavities of di erent dimensions and between insulated and metal bounded cavities.

A two-dimensional eld model of partial discharges in a cylindrical cavity is developed. The sequence of discharges in the cavity is simulated by use of the eld computation program FEMLABR. Discharges are modeled with a voltage and current dependent streamer conductivity and are simulated dynamically to obtain charge and current consistency. It is shown that the frequency dependence of partial discharges is signi - cantly inuenced by the statistical time lag and by the two dielectric time constants related to charge movements on the cavity surface and in the bulk insulation. Simulation results are used to interpret the frequency dependent partial discharge activity in a cylindrical cavity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. viii, 49 p.
Series
Trita-ETS, ISSN 1650-674X ; 2005:13
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-477 (URN)91-7178-169-2 (ISBN)
Presentation
2005-11-11, Sal H1, Teknikringen 33, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20101129Available from: 2005-11-08 Created: 2005-11-08 Last updated: 2010-11-29Bibliographically approved

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CiteExportLink to record
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Citation style
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