Can Nuclear Generation Be Connected to the Uk Electricity Transmission System by Hvdc Technology
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Technical and Economic Analysis of Connecting Nuclear Generation to the National Electricity Transmission System via HVDC Technology Richard Poole School of Engineering and Technology This thesis is submitted to the University of Hertfordshire in partial fulfilment of the requirements of the degree of Doctor of Engineering (EngD) 25th April 2016 Abstract High Voltage Direct Current (HVDC) technology has never before been used to connect a Nuclear Power Plant (NPP) directly to the National Electricity Transmission System (NETS). There are both technical and economic factors which need to be considered and understood before such a technology is adopted for an NPP connection. In this thesis, both technical and economic factors surrounding the suitability of Current Source Converter (CSC) and Voltage Source Converter (VSC) HVDC technology for NPP connections are investigated. Power system models of both HVDC technologies, connected to an NPP, are studied in Power System Computer Aided Design (PSCAD) software. The studies highlight the susceptibility of CSC-HVDC technology to commutation failure during a three-phase fault condition at the inverter, and simulations demonstrate some key benefits of adopting VSC-HVDC technology for NPP connections: provision of independent reactive power support to both the NPP and AC system; black-start capability; fast current reversal for dynamic conditions; and the ability to connect to a weak High Voltage Alternating Current (HVAC) system. The simulations show the vulnerability of VSC-HVDC vector current control when the short circuit ratio of the AC system is very low (<1); in such cases, the Phase Locked Loop (PLL) is affected and power transfer through the VSC-HVDC link may drop to 50% of nominal rating. An economic analysis of HVDC technology development, cost and converter station size is presented. The size of a CSC-HVDC converter station can be much larger than an equivalent- rated VSC due to the additional filters required for reactive power compensation and harmonic mitigation. With the fast evolution of VSC-HVDC technology, the ratings required for an NPP connection are now available. The cost difference between the two technologies can vary from project to project and hence neither one can be ruled out for an NPP connection based only on price. i Acknowledgements The author would like to thank National Grid for the opportunity to carry out this professional Engineering Doctorate (EngD) research project. Particular thanks go to my internal company supervisor Dr Paul Coventry for his continued supervision within National Grid. The author would like to thank the University of Hertfordshire for the chance to study on the EngD programme. Particular thanks go to my academic supervisors Matthew Harrington, Georgios Pissanidis, and Maloud Denai for their continued supervision and guidance throughout the duration of this research programme. Thanks go to my life partner Emma Alaball for her continued support and patience on a year-by- year basis while the author has been working and studying over the last four years. Special thanks goes to ABB Ltd, Siemens, Alstom grid and the Institute of Electrical and Electronic Engineers (IEEE) for the technical reference sources used in the preparation and writing of this thesis. A great deal of thanks goes to Hinkley Point B, Sizewell B, Heysham 2, Wylfa and Torness nuclear power stations for the guided tours and technical information provided to contribute to the nuclear elements of this thesis. The author would like to thank Manitoba Hydro Ltd for providing the PSCAD HVDC models and technical support provided over the last 4 years. ii Table of Contents Abstract .................................................................................................................................................. i Acknowledgements ............................................................................................................................... ii Table of Contents ................................................................................................................................. iii List of Tables ......................................................................................................................................... ix List of Figures ......................................................................................................................................... x Nomenclature .................................................................................................................................... xvii Chapter 1: Introduction ......................................................................................................................... 1 1.1 Motivation ......................................................................................................................................... 1 1.1.1 Connecting nuclear power plants to the NETS .......................................................................... 1 1.1.2 Connecting nuclear power plants by HVDC technology ............................................................ 2 1.2 Objective and main contributions of the thesis ................................................................................ 3 1.3 Outline of the thesis .......................................................................................................................... 5 Chapter 2: Literature Review ................................................................................................................. 8 2.1 NPPs connected by HVDC technology ............................................................................................... 8 2.2 HVDC technology ............................................................................................................................... 9 2.2.1 HVDC versus HVAC .................................................................................................................... 9 2.2.2 Current source converter HVDC technology ........................................................................... 11 2.2.3 VSC-HVDC technology ............................................................................................................. 25 2.3 Nuclear power ................................................................................................................................. 43 2.3.1 Pressurised water reactor ....................................................................................................... 44 2.3.2 Boiling water reactor ............................................................................................................... 44 2.3.3 High temperature advanced gas cooled reactors ................................................................... 45 2.3.4 Layout of a modern NPP .......................................................................................................... 45 2.3.5 Development of an NPP .......................................................................................................... 48 2.3.6 Electric grid vulnerability ......................................................................................................... 49 2.3.7 Interfacing NPPs with AC grids ................................................................................................ 50 2.3.8 Influence of grid disturbances on nuclear power plants ......................................................... 51 2.3.9 History of nuclear power plant disturbances .......................................................................... 53 2.4 Chapter 2 summary ......................................................................................................................... 55 iii Chapter 3: Connecting NPPs by AC Technology .................................................................................. 56 3.1 Introduction ..................................................................................................................................... 56 3.2 Modelling of an NPP connected by AC technology ......................................................................... 56 3.2.1 AC generator model................................................................................................................. 56 3.2.2 AC double-wound transformer model .................................................................................... 58 3.2.3 Autotransformer model........................................................................................................... 61 3.2.4 On-load tap changer model ..................................................................................................... 62 3.2.5 AC overhead transmission line model ..................................................................................... 63 3.2.6 AC induction motor model ...................................................................................................... 66 3.2.7 AC circuit breaker model ......................................................................................................... 67 3.2.8 Load model .............................................................................................................................. 67 3.3 Power system setup ........................................................................................................................ 68 3.3.1 NPP model ..............................................................................................................................