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Partial Discharge Analysis of Stator Insulation at Arbitrary Voltage Waveform Stimulus
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Partial discharge (PD) detection is a powerful tool to diagnose the defects and degradation in high voltage electrical insulation systems. It can be performed in both on-line and off-line conditions. Unlike the on-line PD measurement, the off-line PD test can be performed at other voltages or frequencies besides power-frequency (50 Hz or 60 Hz) sinusoidal voltage. The PD studies in this work were done with other types of voltage waveforms to initiate the discharge, aiming to obtain a better understanding of PD features and its physics, mainly focused on how the charges on the insulating surface affect the discharge process. In particular, this method was studied for application in the stator insulation of high-voltage rotating machines. Several types of arbitrary voltage waveforms have been explored, such as periodic negative step voltage, triangular voltage, trapezoidal voltage and ''square'' voltage.

The PD measurements in this work can be summarized in two parts. One is the fundamental study of corona, surface and cavity discharges in the canonical test cells, using some common insulation materials such as polycarbonate and epoxy. The effect of different materials on corona discharge at periodic negative step voltage pulses was studied in the needle-plane geometry, in comparison with the corona discharge without the insulation material. The evolution of corona pulses shows that the PD repetition rate is strongly dependent on the charges deposited on the insulating surface, and the material properties such as conductivity have a significant effect on the charge decay process during the PD activities. Surface and cavity discharges were compared by the phase resolved PD patterns at several periodic voltage waveforms. The results indicate that the arbitrary voltage waveforms, particularly the square voltage, in off-line PD tests are a potential method for better identification of these two PD sources.

The other part is the practical study for stator winding insulation materials, which consists of mica, epoxy resin and glass-fiber. Specific PD sources that are sphere-plane discharge and crossed-bar discharge based on the stator insulation were created in the laboratory, in order to imitate real insulation such as slot discharges and dielectric bounded cavities. The trapezoidal voltage waveform, including triangular and square voltages was mainly used. Varied ambient conditions such as relative humidity (RH) and temperature were introduced into this part. Slot discharge was modelled by placing a spherical metal electrode above the mica-epoxy insulating surface, leaving a small air gap where PD may occur. The effect of humidity on the sphere-plane discharge shows that a few big discharge pulses in dry air will turn into a larger number of small pulses in humid air probably due to the increasing surface conductivity in a higher humidity condition. Crossed-bar discharge which took place in the air gap between two mica-epoxy surfaces of the cured samples was studied, combined with the influence of the temperature. The variation of PD patterns shows that the effect of temperature on the PD behavior is mainly due to the decreasing PD inception voltage with the increasing temperature.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 83 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2015:019
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-166807ISBN: 978-91-7595-548-3 (print)OAI: oai:DiVA.org:kth-166807DiVA: diva2:812385
Public defence
2015-05-29, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150518

Available from: 2015-05-18 Created: 2015-05-18 Last updated: 2015-05-18Bibliographically approved
List of papers
1. Partial discharge analysis in a needle-plane gap with repetitive step voltage
Open this publication in new window or tab >>Partial discharge analysis in a needle-plane gap with repetitive step voltage
2012 (English)In: 2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE , 2012, 92-95 p.Conference paper, Published paper (Refereed)
Abstract [en]

Partial Discharge (PD) tests are carried out in a needle-plane gap where the plane is covered by an insulating material. The partial discharge activity is studied during application of a periodic negative step voltage, whose duration of the voltage period T1 and the pause time T2 between every two consecutive step voltage pulses could be varied separately to influence the decay of deposited surface charges. Compared with the PDs in the needle-plane setup without dielectric, the effect of dielectric placed on the top of ground electrode on the discharge activity is investigated. The results show for the case of the step voltage with the duration of 100 ms and the pause time of 10 s. The PD activity during the first voltage cycle is significantly different from the others. For a lower voltage, the pulse repetition in the virgin curve reaches a saturation level within the charging period; however, for the higher voltages it becomes more linear increasing.

Place, publisher, year, edition, pages
IEEE, 2012
Series
Conference on Electrical Insulation and Dielectric Phenomena. Annual Report, ISSN 0084-9162
Keyword
Needle-plane, Partial discharge activity, Partial discharge analysis, Pulse repetition, Saturation levels, Step voltages, Voltage cycle
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-105859 (URN)10.1109/CEIDP.2012.6378730 (DOI)000316899800019 ()2-s2.0-84872095186 (Scopus ID)978-1-4673-1252-3 (ISBN)
Conference
2012 IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2012; Montreal, QC; Canada; 14 October 2012 through 17 October 2012
Note

QC 20121128

Available from: 2012-11-28 Created: 2012-11-28 Last updated: 2015-05-18Bibliographically approved
2. Effect of Dielectric Material on Decay of Surface Charge Deposited by Corona Discharge
Open this publication in new window or tab >>Effect of Dielectric Material on Decay of Surface Charge Deposited by Corona Discharge
Show others...
2013 (English)In: Proceedings of the 18th International Symposium on High Voltage Engineering (ISH), 2013, 753-758 p.Conference paper, Published paper (Refereed)
Abstract [en]

This work investigates the effect of different dielectric barriers on coronadischarge in the needle-plane geometry, where a layer of dielectric material was placedover the surface of the plane electrode. Different dielectric materials used werepolytetrafluoroethylene (PTFE), polyethylene (PE), polycarbonate (PC), polyvinylchloride(PVC), epoxy and pressboard. The discharges were generated by the application ofperiodic negative step voltage pulses. The results show that the evolution of coronapulses over time depends on the dielectric properties of the barriers. Unlike pressboardwith a higher conductivity, the dielectric materials with a lower conductivity such as PTFEand PE would have more surface charges deposited on its surface during the firstcharging period of 100 ms, and the charges would not disappear during the relaxationperiod of 10 s, therefore, the discharge activities can be reduced significantly after thefirst charging period.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-166551 (URN)
Conference
18th International Symposium on High Voltage Engineering (ISH), 2013 Korea
Note

QC 20150518

Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2017-06-02Bibliographically approved
3. Enhanced Distinction of Surface and Cavity Discharges by Trapezoid-based Arbitrary Voltage Waveforms
Open this publication in new window or tab >>Enhanced Distinction of Surface and Cavity Discharges by Trapezoid-based Arbitrary Voltage Waveforms
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-166556 (URN)
Note

QS 2015

Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2015-05-20Bibliographically approved
4. Effect of Humidity on Partial Discharge in a Metal-dielectric Air Gap on Machine Insulation at Trapezoidal Testing Voltages
Open this publication in new window or tab >>Effect of Humidity on Partial Discharge in a Metal-dielectric Air Gap on Machine Insulation at Trapezoidal Testing Voltages
(English)Manuscript (preprint) (Other academic)
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-166554 (URN)
Note

QS 2015

Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2015-05-20Bibliographically approved

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