VOLTAGE BALANCING ON THREE- PHASE LOW VOLTAGE FEEDER A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy in the Faculty of Engineering and Physical Sciences 2015 YUN LI SCHOOL OF ELECTRICAL AND ELECTRONIC ENGINEERING Content Content Content ............................................................................................................ 2 List of Figures ................................................................................................. 6 List of Tables ................................................................................................. 10 Abbreviations ................................................................................................ 11 Abstract ......................................................................................................... 13 Declaration .................................................................................................... 14 Copyright Statement...................................................................................... 15 Acknowledgement ......................................................................................... 16 Publications ................................................................................................... 17 Chapter 1 ....................................................................................................... 18 Introduction ................................................................................................... 18 1.1 Background ............................................................................................................. 18 1.1.1 Electric vehicle ................................................................................................. 19 1.1.2 Heat pump ......................................................................................................... 20 1.2 Motivation and objectives ....................................................................................... 21 1.3 Contribution of the work ......................................................................................... 22 1.4 Structure of the thesis .............................................................................................. 25 Chapter 2 ....................................................................................................... 27 Voltage Imbalance in LV Networks ............................................................. 27 2.1 Introduction ............................................................................................................. 27 2.2 Low voltage network ............................................................................................... 28 2.2.1 LV network in the UK ...................................................................................... 28 2.2.2 LV networks around the world ......................................................................... 35 2.3 Voltage imbalance ................................................................................................... 39 2.3.1 Introduction ....................................................................................................... 39 2.3.2 Expressions ....................................................................................................... 40 Page | 2 Content 2.3.3 Associated standards ......................................................................................... 44 2.3.4 Causes ............................................................................................................... 46 2.3.5 Consequences.................................................................................................... 48 2.4 Voltage imbalance mitigation.................................................................................. 52 2.4.1 Conventional mitigating methods ..................................................................... 52 2.4.2 Modern mitigating methods .............................................................................. 55 2.5 Voltage limits .......................................................................................................... 59 2.6 Summary ................................................................................................................. 60 Chapter 3 ....................................................................................................... 62 Scott Transformer based Voltage Balancing Method ................................... 62 3.1 Introduction ............................................................................................................. 62 3.2 Voltage regulation using transformers and tap changers ........................................ 63 3.2.1 Basic control ..................................................................................................... 63 3.2.2 Voltage magnitude regulation ........................................................................... 65 3.2.3 Voltage phase angle regulation ......................................................................... 70 3.2.4 Independent voltage magnitude and phase angle regulation ............................ 73 3.3 Overview of the proposed method .......................................................................... 75 3.4 Scott transformer ..................................................................................................... 77 3.5 Phase regulating system .......................................................................................... 86 3.6 Control algorithm .................................................................................................... 88 3.7 Summary ................................................................................................................. 92 Chapter 4 ....................................................................................................... 94 Computer Simulation of ST based Voltage Balancing Method ................... 94 4.1 Introduction ............................................................................................................. 94 4.2 Modelling of ST based voltage balancing system ................................................... 95 4.3 Voltage balancing using tap changers ..................................................................... 98 4.3.1 Simulation methodology ................................................................................... 98 4.3.2 Three-phase balancing method ......................................................................... 99 4.3.3 Simulation results ........................................................................................... 102 4.4 Application in a typical UK distribution network ................................................. 106 4.4.1 Simulation methodology ................................................................................. 106 Page | 3 Content 4.4.2 Distribution network model ............................................................................ 107 4.4.3 Simulation results ........................................................................................... 109 4.5 Summary ............................................................................................................... 117 Chapter 5 ..................................................................................................... 118 Physical Test of ST based Voltage Balancing Method & Associated Simulation ................................................................................................... 118 5.1 Introduction ........................................................................................................... 118 5.2 Experimental methodology ................................................................................... 119 5.3 Experimental plant ................................................................................................ 119 5.3.1 Physical voltage balancing system ................................................................. 120 5.3.2 Microprocessor based control system ............................................................. 120 5.3.3 Low voltage feeder ......................................................................................... 122 5.4 Experimental results .............................................................................................. 122 5.5 Associated simulation study .................................................................................. 125 5.5.1 Simulation methodology ................................................................................. 125 5.5.2 Simulation results ........................................................................................... 125 5.6 Summary ............................................................................................................... 128 Chapter 6 ..................................................................................................... 130 Monte Carlo Study on Impact of EVs & HPs on LV Feeder Voltages ...... 130 6.1 Introduction ........................................................................................................... 130 6.2 Impact of EVs and HPs on distribution networks ................................................. 131 6.3 Simulation methodology ....................................................................................... 134 6.4 Statistical model of EV demand ...........................................................................