Partial Discharge Diagnostic Testing of Electrical Insulation Based on Very Low Frequency High Voltage Excitation

Partial Discharge Diagnostic Testing of Electrical Insulation Based on Very Low Frequency High Voltage Excitation Hong Viet Phuong Nguyen Supervisor: Associate Professor Toan Phung A thesis in fulfilment of the requirements for the degree of Doctor of Philosophy School of Electrical Engineering and Telecommunications Faculty of Engineering University of New South Wales March 2018 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: NGUYEN First name: HONG VIET PHUONG Other name/s: Abbreviation for degree as given in the University calendar: Ph.D. School: Electrical Engineering and Telecommunications Faculty: Engineering Title: Partial Discharge Diagnostic Testing of Electrical Insulation based on Very Low Frequency High Voltage Excitation Abstract 350 words maximum: (PLEASE TYPE) High voltage diagnostic testing such as partial discharge measurement plays a vital role in determining the condition of equipment insulation. Performing the testing with applied voltage at very low frequency significantly reduces the power required from the supply. However, partial discharge behaviour varies with frequency and thus existing knowledge on interpretations of partial discharge at power frequency cannot be directly applied to test results measured at very low frequency for insulation diagnosis. The motivation of this research is to study partial discharge behaviours at very low frequency and search for physical explanations of such differences. Laboratory experiments were performed to gather data on corona discharge and internal discharge using a commercial measurement system. In the tests, individual discharge events were recorded including magnitude and phase position to enable phase-resolved pattern analysis. A comprehensive study of corona discharges at different applied voltage waveforms, such as sinusoidal wave and square wave, was carried out under the excitation at very low frequency. Experimental results showed that the inception voltage is dependent on applied voltage waveforms. Furthermore, the increase of ambient temperature results in larger discharge magnitude and causes corona discharges to occur earlier in the phase of the voltage cycle. Characteristics of internal discharges in a cavity are strongly dependent on applied frequency. A dynamic model for numerical computation was developed to study this dependence. This model has a minimum set of adjustable parameters to simulate discharges in the cavity. Simulation results revealed that charge decay has a significant contribution to discharge characteristics at very low frequency. Charge decay causes reduction of the initial electron generation rate which results in lower discharge magnitude and repetition rate. Also, the statistical time lag of discharge activities is calculated and it exhibits strong dependence on applied frequency. The contributions of this research include the development of a discharge model to characterise physical processes of discharge in a cavity, discussions on differences in partial discharge characteristics at very low frequency and power frequency as a function of cavity size, voltage waveforms and ambient temperatures. These findings provide better understanding of discharge behaviours at very low frequency excitation. 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). …………………………………………… ……………………………………..……………… ……….……………… Signature Witness Signature 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. 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 …………………………………………….............................. 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……………………………………………................................ 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……………………………………………................... To my loving family…….. Dedicated to Ruby……. Acknowledgement The journey of my PhD research has not been easy and smooth. Without support from many people along the way, it would not have been possible to complete this thesis. First and foremost, I would like to sincerely thank my supervisor, Associate Professor Toan Phung, for guiding me through every single step of this research. I truly appreciate your valuable comments, advice, corrections and endless support over the past four years regardless of the day or night, weekday or weekend, working time or holiday. I also express my appreciation to all the technical staff of the School of Electrical Engineering and Telecommunications, especially Mr Zhenyu Liu for accompanying me in the UNSW High Voltage laboratory during the experiments. I appreciate the time we spent together working on the experimental equipment. It would not have been possible to come to UNSW Australia without financial support from the Australia Awards Scholarship. I would like to acknowledge all the support from the scholarship liaison officers during my PhD candidature. I also thank all my friends who shared memorable times. To Thinh, Minh, Hau, Dai and other Vietnamese students, thank you for broadening my cultural perception. To Hana, Tariq, Majid, Morsalin and other international friends, I really appreciate your friendship. Last but not least, no words can express my deepest gratitude to my parents and parents-in-law. Thank you, Dad, for making me tougher through your hard words. Thanks Mom for your understanding and always being on my side. To my wife and son, you are the best. Apologies are not enough for all your sufferings during the time without me. Thank you so much for being with me during the ups and downs in life. I love you all! page i Abstract Electrical insulation plays an important role in the proper functioning of high voltage power system equipment/components. Examining the condition of insulation is crucial to keep the equipment safe and functioning efficiently. High voltage diagnostic tests, in particular partial discharge measurements, are very effective in detecting early signs of insulation damage. This type of diagnostic test is generally conducted at the power frequency to emulate normal operating condition. However, it is difficult to perform the test on-site due to the large reactive power required when testing high-capacitance objects such as cables. An alternative approach is to conduct the test at very low frequency excitation, commonly at 0.1 Hz, because the required power is proportional to the applied frequency and thus is significantly reduced. However, partial discharge behaviour varies with frequency and thus existing knowledge on interpretations of partial discharge at power frequency cannot be directly applied to test results measured at very low frequency for

Load more