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Modelling of cavity partial discharges at variable applied frequency
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The presence of partial discharges (PD) in high voltage components is generally a sign of defects and degradation in the electrical insulation. To diagnose the condition of high voltage insulation, PD measurements is commonly used. The Variable Frequency Phase Resolved PD Analysis (VF-PRPDA) technique measures PD at variable frequency of the applied voltage. With this technique, the frequency dependence of PD can be utilized to extract more information about the insulation defects than is possible from traditional PD measurements at a single applied frequency.

In this thesis the PD process in a disc-shaped cavity is measured and modelled at variable frequency (0.01 - 100 Hz) of the applied voltage. The aim is to interpret the PD frequency dependence in terms of physical conditions at the cavity. The measurements show that the PD process in the cavity is frequency dependent. The PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, change with the varying frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the size of the cavity and the location of the cavity (insulated or electrode bounded).

A physical model is presented and used to dynamically simulate the sequence of PDs in the cavity at different applied frequencies. The simulations show that essential features in the measured PD patterns can be reproduced. The PD frequency dependence is interpreted as a variation in influence on the PD activity from the statistical time lag of PD and the charge transport in the cavity surface, at different applied frequencies. The simulation results also show that certain cavity parameters, like the cavity surface conductivity and the rate of electron emission from the cavity surface, change with the time between consecutive PDs, and accordingly with the applied frequency. This effect also contributes to the PD frequency dependence.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , viii, 74 p.
Series
Trita-EE, ISSN 1653-5146 ; 2008:018
Keyword [en]
partial discharges, measurements, modelling, variable frequency, cavities, disc-shaped, polycarbonate
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4756ISBN: 978-91-7178-927-3 (print)OAI: oai:DiVA.org:kth-4756DiVA: diva2:13791
Public defence
2008-06-04, F3, Lindstedtsvägen 26, Stockholm, 13:15
Opponent
Supervisors
Note
QC 20100722Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-22Bibliographically approved
List of papers
1. Variable frequency partial discharge analysis of in-service aged machine insulation
Open this publication in new window or tab >>Variable frequency partial discharge analysis of in-service aged machine insulation
2003 (English)In: Proceedings Nordic Insulation Symposium, 2003, 29-35 p.Conference paper, Published paper (Refereed)
Keyword
variable frequency, phase resolved, partial discharge, machine insulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8456 (URN)
Conference
Nordic Insulation Symposium, Tampere, June 11-13, 2003
Note
QC 20100722Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-11-29Bibliographically approved
2. Modelling of Partial Discharge Spectra Measured with Variable Applied Frequency
Open this publication in new window or tab >>Modelling of Partial Discharge Spectra Measured with Variable Applied Frequency
2003 (English)In: Proceedings of the 7th international conference on properties and applications of dielectric materials, 2003, 839-842 p.Conference paper, Published paper (Refereed)
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.

Keyword
Capacitance, Computer simulation, Electric conductivity, Electric fields, Electric impedance, Electric insulation, Electric network analysis, Electric variables measurement, Permittivity
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8457 (URN)10.1109/ICPADM.2003.1218552 (DOI)000186114700209 ()0-7803-7725-7 (ISBN)
Conference
7th International Conference on Properties and Applications of Dielectric Materials, NAGOYA, JAPAN, JUN 01-05, 2003
Note
QC 20100722Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-11-29Bibliographically approved
3. Measured Partial Discharge Inception Voltage for a Cavity at Different Applied Frequencies
Open this publication in new window or tab >>Measured Partial Discharge Inception Voltage for a Cavity at Different Applied Frequencies
2007 (English)In: Nordic Insulation Symposium (Nord-IS 07), 2007, 59-62 p.Conference paper, Published paper (Refereed)
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.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8458 (URN)
Note
QC 20100722Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-22Bibliographically approved
4. Modeling Partial Discharges in a Cavity at Different Applied Frequencies
Open this publication in new window or tab >>Modeling Partial Discharges in a Cavity at Different Applied Frequencies
2007 (English)In: Annual Conference on Electrical Insulation and Dielectric Phenomena: Vancouver, CANADA, OCT 14-17, 2007, 2007, 132-135 p.Conference paper, Published paper (Refereed)
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.

Keyword
Dielectric phenomenon; Electrical insulation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8459 (URN)10.1109/CEIDP.2007.4451518 (DOI)000254276700031 ()2-s2.0-51249115842 (Scopus ID)978-1-4244-1481-9 (ISBN)
Note
QC 20100722Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2010-07-22Bibliographically approved
5. Measured Applied Frequency Dependence of Partial Discharges in Disc-Shaped Cavities
Open this publication in new window or tab >>Measured Applied Frequency Dependence of Partial Discharges in Disc-Shaped Cavities
2007 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135Article in journal (Other academic) Submitted
Keyword
partial discharges; measurements; variable frequency; cavities; disc-shaped; electrode bounded; polycarbonate
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8460 (URN)
Note
QS 20120316Available from: 2008-05-16 Created: 2008-05-16 Last updated: 2017-12-14Bibliographically approved
6. Partial discharges in a cavity at variable applied frequency part 2: Measurements and modeling
Open this publication in new window or tab >>Partial discharges in a cavity at variable applied frequency part 2: Measurements and modeling
2008 (English)In: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 15, no 6, 1610-1616 p.Article in journal (Other academic) Published
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.

Keyword
partial discharges; measurements; modeling; variable frequency; cavities; disc-shaped; polycarbonate
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-8461 (URN)10.1109/TDEI.2008.4712664 (DOI)000261308800017 ()2-s2.0-58149114581 (Scopus ID)
Note
QC 20100722. Updated from submitted to published, QC 20120314. Previous title: Measurement and Modeling of Partial Discharges in a Cavity at Variable Applied FrequencyAvailable from: 2008-05-16 Created: 2008-05-16 Last updated: 2017-12-14Bibliographically approved

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