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Effect of Dielectric Material on Decay of Surface Charge Deposited by Corona Discharge
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
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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.

Place, publisher, year, edition, pages
2013. 753-758 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-166551OAI: oai:DiVA.org:kth-166551DiVA: diva2:811271
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
In thesis
1. Partial Discharge Analysis of Stator Insulation at Arbitrary Voltage Waveform Stimulus
Open this publication in new window or tab >>Partial Discharge Analysis of Stator Insulation at Arbitrary Voltage Waveform Stimulus
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:nbn:se:kth:diva-166807 (URN)978-91-7595-548-3 (ISBN)
Public defence
2015-05-29, H1, Teknikringen 33, KTH, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20150518

Available from: 2015-05-18 Created: 2015-05-18 Last updated: 2015-05-18Bibliographically approved

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Taylor, Nathaniel

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