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Partial discharge patterns in a cavity embedded in oil-impregnated papers: Part 2: Effect of thermalageing
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0003-1766-8077
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
(English)Article in journal (Other academic) Submitted
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-105039OAI: oai:DiVA.org:kth-105039DiVA: diva2:568008
Note

QS 2012

Available from: 2012-11-15 Created: 2012-11-15 Last updated: 2015-02-06Bibliographically approved
In thesis
1. Effect of HV Impulses on Partial Discharge Activity in Oil-Impregnated Paper Insulation
Open this publication in new window or tab >>Effect of HV Impulses on Partial Discharge Activity in Oil-Impregnated Paper Insulation
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

High voltage (HV) transients in electrical power systems are mainly caused by lightning strikes and switching operations.  The high voltage transient from its point of origin can propagate in either direction in the electrical power transmission line, and if its magnitude would be below the Basic Insulation Level (BIL) of the equipment for impulse voltage, it can reach the terminals of the equipment without being dissipated by surge arresters.  The dielectric properties of a particular insulation at the instant of interaction with a high voltage transient would determine the level of the degradation of the electrical insulation caused by the high voltage transient. This thesis suggests on-line diagnostic techniques for monitoring the oil-impregnated paper condenser bushings by utilizing the naturally occurring HV transients in electrical power systems.

The aim of the first experiment was to investigate the partial discharge (PD) characteristics of the PD defects which are likely to be found in oil-imregnated paper condenser bushings. In order to understand the condition at which the HV impulses would cause the change in phase resolved partial discharge (PRPD) patterns, four more experiments were performed. The second experiment was set in such a way that the effect of HV impulses alone could be investigated. On the other hand, the third experiment was set to examine the effect of PD-ageing at elevated AC voltage. The fourth experiment aimed in investigating the effect of combined PD-ageing at elevated AC voltage and the HV impulses. In order to investigate how different electrical stresses affect the dielectric properties of the oil-impreganted paper insulation, the fifth experiment about the dielectric spectroscopy (DS) in frequency domain was performed.

The measurement results presented in this thesis show that high voltage impulses can have a large impact on the behavior of PRPD patterns if the test sample is aged by partial discharges, but a smaller impact when the test sample is unaged. The measurement results also show that the degradation of the oil-impregnated papers is much faster when the oil-impregnated papers are suffered from the combination of the HV impulses and the PD activity at elevated AC voltage than when they are suffered from the PD activity at elevated AC voltage alone.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 70 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:054
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-104829 (URN)978-91-7501-543-9 (ISBN)
Presentation
2012-11-30, H21, Teknikringen 33, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121115

Available from: 2012-11-15 Created: 2012-11-13 Last updated: 2012-11-16Bibliographically approved
2. Partial Discharge Signatures of Defects in Insulation Systems Consisting of Oil and Oil-impregnated Paper
Open this publication in new window or tab >>Partial Discharge Signatures of Defects in Insulation Systems Consisting of Oil and Oil-impregnated Paper
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Partial discharge measurement is a common method for monitoring and diagnostics of power transformers, and can detect insulation malfunctions before they lead to failure. Different parameters extracted from the measured PD activity can be correlated to the PD source, and as a result it is possible to identify the PD source by analyzing the PD activity.

In this thesis, possible defects that could cause harmful PDs in transformers were investigated. These defects include corona in oil, a void in pressboard, a metal object at floating potential, surface discharge in oil, a free bubble in oil and small free metallic particles in oil. The characteristics of disturbing discharge sources were analyzed, like corona in air, surface discharge in air, and discharge from an unearthed object near to the test setup.

The PD activity was recorded both in the time domain and phase domain, and possible characteristics for each PD pattern and waveform were extracted in order to find the best characteristic for the purpose of classification.

The results show that in the phase domain parameters such as phase of occurrence, repetition rate and shape of PD Pattern are most suitable for classification while magnitude of discharge can only be useful in specific cases. The results show that the PD waveforms correlated to different defects are similar; however the time domain data include all the information from the phase domain, and also has the power to identify the number of PD sources.

 The PD dependency on temperature was investigated on the four test objects including surface discharges in oil, corona in oil, bubble discharges in oil, and metal object at floating potential. The effect of humidity was investigated for corona in oil. The results show that at higher temperature the corona activity in oil and PD activity due to a metal object at floating potential in oil decrease. However, for a bubble in oil and for surface discharge in oil the PD activity increases with the increase of the oil temperature. It was shown that the amount of moisture in oil has a strong impact on number of corona pulses in oil.

The last part focused on ageing of oil-impregnated paper due to PD activity. Investigation was made of the behavior of PD activity and its corresponding parameters such as PD repetition rate and magnitude, from inception until complete puncture breakdown. The results show that both the number and magnitude of PD increase over time until they reach to a peak value. After this point over time both curves decrease slowly, and eventually full breakdown occurs.

The effect of thermal ageing of oil impregnated paper on time to breakdown and PD parameters was investigated. The results show that thermal aging of oil-impregnated paper increases the number and magnitude of PD. Dielectric spectroscopy was performed on the samples before and after PD ageing and the result was used in order to explain the behavior of PD over time.

Place, publisher, year, edition, pages
KTH, Stockholm: KTH Royal Institute of Technology, 2012. viii, 67 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:059
Keyword
partial discharge, transformer, oil, ageing, temperature, PD classification
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-105785 (URN)978-91-7501-573-6 (ISBN)
Presentation
2012-12-07, H21, Teknikringen 33, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20121129

Available from: 2012-11-29 Created: 2012-11-26 Last updated: 2015-02-06Bibliographically approved

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Ghaffarian Niasar, Mohamad

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