SYMPATHETIC INRUSH CURRENTS IN TRANSFORMER ENERGISATION Hana Abdull Halim Supervisor: A/Prof. 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 The University of New South Wales January, 2018 To my parents, husband, and daughter For the endless support, love and pray i ACKNOWLEDGEMENTS The path toward this thesis completion was not easy. The completion of this thesis would never been possible without many special people who supported and stuck with me along the way. Firstly, I would like to express my sincere gratitude to my supervisor, Assoc. Prof. Dr. Toan Phung who gave me invaluable advice and guidance throughout the project. Co-supervisor, Prof. Dr. John Fletcher, for the heart-warming support you offered when needed and Dr. Daming Zhang whom I always turn for help and feedback. I also owe a great deal of thanks to the technical staff, Mr. Zhenyu Liu for his technical support and thoughtful concern. To other students that cross paths in the laboratory works especially Mr. Richard, Mr. Roger, Mr. Jason and Mr. Karthik; our discussions of the experiments have definitely been invaluable for my project. I also want to acknowledge the funding received from the Ministry of Higher Education Malaysia together with Universiti Malaysia Perlis (UniMAP), for the student sponsorship, and from the University of New South Wales and the IEEE DEIS NSW for conference travel assistance. Not to forget my all mates during PhD journey, Ain, Kimah, Sab, Yaty and all Malaysian Postgraduates Students and their families. To lab and officemates especially Sithumini and Phuong, thank you for the knowledge sharing and friendship. It makes my PhD life unforgettable. To my parents and parents in law, Abdull Halim Abdul, Fazilah Abdullah, Zainuddin Zakaria and Hosmah Darus who have always supported and been praying for me for all these years, thank you. For your tired and sick days that we were not able to be around, sorry seems not enough. I am also indebted to my siblings, in-laws and cousins. My heartfelt thank goes to all of you for always believing and supporting me during this challenging period. Last but not least, special thanks to my beloved husband, Zaki Zainuddin who remains willing to engage with the struggles, sacrifice his career and at the same time become a loving and supportive partner. To my daughter, Hana Zaheen, thank you for being so independent and yet brighten up each day during my hardest time. You are such a blessing. Once again, to all the people mentioned earlier, the success of this project is partly due to your support and blessings. Thank you. ABSTRACT Power transformers are critical components of the electricity networks. It is common knowledge that transformer energisation causes a number of slow-front inrush current transient problems. With the increase of distributed generations with inherent high intermittency resulting in more switching events, the transformers in service are increasingly vulnerable to electrical transients. This thesis is concerned with transformer energisation inrush, particularly focussing on the sympathetic inrush in supply networks with parallel-connected transformers. To perform the investigation, transformer models are developed using MATLAB/Simulink, and simulations are also carried out using PSCAD/EMTDC software. The study is initiated with the modelling using the classic Steinmetz model. Subsequently, in order to improve the accuracy, the Jiles-Atherton model is considered whereby its parameters are based on magnetic quantities and computed via a series of differential evaluation algorithms. The results demonstrated a significant improvement of accuracy of the transformer model. The findings obtained from simulation are then validated with laboratory experiments. One, two, and/or three single-phase 16 kVA, 11kV/250V oil-immersed distribution transformers are tested to examine inrush transients under different energisation cases. Special focus is placed on the first inrush peak, to determine whether or not the level of the incoming inrush can be predicted. This thesis also analyses the sympathetic inrush prolonging effects on voltage sags. The impacts of flux density and system resistance as well as the number of simultaneously energised transformers are also investigated. The contributions of this research include the development of an improved transformer model for simulating the sympathetic inrush using a combination of the classic model and Jiles-Atherton hysteresis model, the proposal of measurement methodology to extract model parameters for transformers with only nameplate data, the design and implementation of a point-on-wave switch, the laboratory works on mitigating parallel- connected inrush transients, the assessment of the effects and characteristics of sympathetic inrush through observing waveform patterns and the prediction of the Page i incoming peak inrush, and the analysis of voltage sagging. Also, this research examines the growing Australia‘s wind energy development and demonstrates the emerging problem of sympathetic inrush in parallel-connected wind turbine transformers. All the above research contributions are achieved with the completion of this thesis. Page ii Contents ABSTRACT. .................................................................................................................... i LIST OF TABLES ....................................................................................................... vii LIST OF FIGURES ....................................................................................................... ix CHAPTER 1 INTRODUCTION .................................................................................... 1 1.1 Background of Study ................................................................................................ 1 1.2 Background Information ........................................................................................... 3 1.3 Problem Statement .................................................................................................... 8 1.4 Research Methodology.............................................................................................. 9 1.5 Objectives of the Research ...................................................................................... 11 1.6 Original Contributions ............................................................................................ 12 1.7 Thesis Outline ......................................................................................................... 13 1.8 Publications ............................................................................................................. 15 CHAPTER 2 LITERATURE REVIEW ....................................................................... 17 2.1 Transformer Energisation Transients ...................................................................... 17 2.2 Transformer Modelling for Inrush Current Studies ................................................ 18 2.3 Transformer Saturation and Inrush Current ............................................................ 23 2.4 Sympathetic Inrush Current Transients ................................................................... 26 2.5 Mitigation Techniques for Transformer Energisation Transients ........................... 33 2.6 Voltage Distortion Issue in Transformer Energisation Transients .......................... 35 2.7 Pseudo-inrush in Transformer Re-Energisation ...................................................... 37 Page iii 2.8 Sympathetic Interaction in Wind Farm Integration ................................................ 38 2.9 Summary ................................................................................................................. 39 CHAPTER 3 TRANSFORMER AND SYSTEM COMPONENT MODELLING IN THE STUDY OF TRANSFORMER ENERGISATION TRANSIENTS ............................................................................................................... 41 3.1 Background of Transformer Modelling .................................................................. 41 3.2 Transformer Modelling in PSCAD/EMTDC .......................................................... 45 3.3 Basic Transformer Modelling ................................................................................. 49 3.4 Computation of Losses in Transformers ................................................................. 58 3.5 Magnetic Core Saturation and Hysteresis ............................................................... 63 3.6 Estimation and Assumptions in the Modelling Study ............................................. 68 3.7 Circuit Breaker Modelling ...................................................................................... 68 3.8 Discussion and Summary ........................................................................................ 69 CHAPTER 4 IMPROVED TRANSFORMER MODELLING VIA THE JILES- ATHERTON MODEL .......................................................................... 71 4.1 Background ............................................................................................................. 71 4.2 Transformer Modelling using Jiles-Atherton .......................................................... 73 4.3 Jiles-Atherton in PSCAD/EMTDC ......................................................................... 76 4.4 Inverse Jiles-Atherton ............................................................................................. 78 4.5 Jiles Atherton Model Parameter Estimation ........................................................... 82 4.6 Signal De-noising .................................................................................................... 87 4.7 Results and Discussion ............................................................................................ 89 Page iv