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Transformer Winding Deformation and Insulation Characteristic Effects on Frequency Response Analysis

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Transformer Winding Deformation and Insulation Characteristic Effects on Frequency Response Analysis Transformer Winding Deformation and Insulation Characteristic Effects on Frequency Response Analysis By Mehdi BAGHERI Supervisor: Dr.Toan PHUNG Co-supervisor: A/Prof. Trevor BLACKBURN A THESIS IN FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY SCHOOL OF ELECTRICAL ENGINEERING AND TELECOMMUNICATIONS FACULTY OF ENGINEERING March 2014 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: BAGHERI First name: Mehdi Other name/s: Abbreviation for degree as given in the University calendar: Ph.D. School: Electrical Engineering and Telecommunications Faculty: Engineering Title: Transformer Winding Deformation and Insulation Characteristic Effects on Frequency Response Analysis Abstract 350 words maximum: Frequency Response Analysis (FRA) is considered an accurate, fast, economical and non-destructive method for the detection of winding deformation within power transformers, providing detailed information on electrical properties of this asset. Changes in winding configuration, as well as other transformer active part structures would almost certainly cause variation in the frequency response spectrum. This can be exploited for mechanical defect recognition. On the other hand, transformer oil deterioration, temperature variation as well as water absorbed by the paper can cause transformer insulation characteristics to change over the time. In fact, capacitances, self- and mutual inductances and conductor resistances might be altered due to any changes in above mentioned factors. In turn, the frequency response of the winding will change accordingly. Thus in the interpretation of the FRA spectrum for evidence of winding deformation, the influence of insulation characteristic on the spectrum must be taken into consideration. FRA deviation due to the winding deformation or insulation characteristic changes becomes even more complicated to interpret when FRA baseline and measured spectra are taken under different temperatures and moisture contents. In such a case, existing FRA evaluation methods using statistical indicators are likely to reveal incorrect prognosis. Hence in this thesis, the aim of the research is to distinguish the insulation characteristic impacts on FRA spectrum from winding deformation. To this end, resonances and anti-resonances in FRA spectrum over different frequency bands are examined in detail and interpretations are provided. FRA deviation due to the transformer winding deformation is discussed analytically, modelled and simulated. The results are then compared to practical measurements. Insulation characteristic changes in transformer are studied through temperature and moisture variations to recognise their influences on FRA data. FRA capability in recognising moisture migration from the paper insulation of transformer winding is recommended and its potential application in transformer winding dry-out process evaluation is revealed in this research. Finally, possible offline and online solutions to distinguish the impact of moisture and temperature variations on winding deformation diagnosis are provided. Online FRA measurement and its required setup as a potential future approach in transformer condition monitoring are discussed. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). ……………………………………………………… …………………………………………… ……14/06/2014………. Signature Witness Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed………………………………………….............. Date……………14/06/2014.………………….............. AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed………………………………………….............. Date……………14/06/2014.………………….............. ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed………………………………………….............. Date……………14/06/2014.………………….............. A THESIS DEDICATED TO MY FATHER AND SISTER IN LOVING MEMORY OF MY MOTHER Acknowledgment I would like to express my sincere gratitude to my supervisor, Dr. Toan PHUNG, for his continuous support throughout my PhD study. I cannot thank enough for his guidance, insightful instruction, and ceaseless encouragements during the past years. I would also like to give my special appreciation to my co-supervisor, A/Prof. Trevor BLACKBURN. His inspiring minds and firm support have definitely taken my research to another level. I have been deeply influenced by his enthusiasm for science, ambitious heart in research, and greatest dedication to work. In addition, I would deeply thank Dr. Mohammad SALAY NADERI my former supervisor for his detailed instruction and fruitful discussions. His ongoing and valuable advice allowed me to expand my knowledge broadly and gain very useful skills. Last but not least, I am forever indebted to my father and sister, who gave me a beautiful life and supported me for studying overseas emotionally. I also give my special thank to my mother who could not survive to see this great time in my life. It is your love that embraced me through the PhD and my life. Abstract Frequency Response Analysis (FRA) is considered an accurate, fast, economical and non- destructive method for the detection of winding deformation within power transformers, providing detailed information on electrical properties of this asset. Changes in winding configuration, as well as other transformer active part structures would almost certainly cause variation in the frequency response spectrum. This can be exploited for mechanical defect recognition. On the other hand, transformer oil deterioration, temperature variation as well as water absorbed by the paper can cause transformer insulation characteristics to change over the time. In fact, capacitances, self- and mutual inductances and conductor resistances might be altered due to any changes in above mentioned factors. In turn, the frequency response of the winding will change accordingly. Thus in the interpretation of the FRA spectrum for evidence of winding deformation, the influence of insulation characteristic on the spectrum must be taken into consideration. FRA deviation due to the winding deformation or insulation characteristic changes becomes even more complicated to interpret when FRA baseline and measured spectra are taken under different temperatures and moisture contents. In such a case, existing FRA evaluation methods using statistical indicators are likely to reveal incorrect prognosis. Hence in this thesis, the aim of the research is to distinguish the insulation characteristic impacts on FRA spectrum from winding deformation. To this end, resonances and anti-resonances in FRA spectrum over different frequency bands are examined in detail and interpretations are provided. FRA deviation due to the transformer winding
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