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Corona in oil as a function of geometry, temperature and humidity
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0003-1766-8077
KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
2010 (English)In: 2010 Annual Report Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), IEEE , 2010, 5724061- p.Conference paper, Published paper (Refereed)
Abstract [en]

Corona discharge in oil is one of a number of important defects that may exist in a power transformer. This paper investigates the corona in oil from a needle-plane geometry. Different aspect ratios of the geometry are investigated as well as the temperature dependence from 25 to 100 °C. The corona discharges are measured both in time domain with oscilloscopes and as phase resolved patterns. By using COMSOL, a simple simulation of the electric field in the needle-plane geometry is computed. Simulation of electrical field around the needle tip for different needle length and distance from the needle tip to plane is performed. An amplification factor of electrical field around the tip, according to these parameters is developed. By considering corona inception voltage as a function of electrical field around the tip, by using the same geometries for simulation and measurement, inception field for corona in oil as a function of electrical field is calculated. The results show the dependency of corona inception voltage, discharge magnitude and repetition rate on the geometrical parameters, temperature and humidity.

Place, publisher, year, edition, pages
IEEE , 2010. 5724061- p.
Series
Conference on Electrical Insulation and Dielectric Phenomena. Annual Report, ISSN 0084-9162
Keyword [en]
Corona, Geometry, Humidity, Needles, Petroleum, Temperature measurement, Voltage measurement
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-105865DOI: 10.1109/CEIDP.2010.5724061Scopus ID: 2-s2.0-79952932840ISBN: 978-142449470-5 (print)OAI: oai:DiVA.org:kth-105865DiVA: diva2:572629
Conference
2010 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2010; West Lafayette, IN; United States; 17 October 2010 through 20 October 2010
Note

QC 20121128

Available from: 2012-11-28 Created: 2012-11-28 Last updated: 2015-02-06Bibliographically approved
In thesis
1. 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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