Improved Generation Dispatch In Power Systems Imperial College of Science, Technology and Medicine t A thesis submitted for the degree of Doctor of Philosophy of the University of London and for the diploma of Membership of Imperial College -by- Fergal McNamara Electrical Energy Systems Section Department of Electrical Engineering Imperial College August 1990 Page i Improved Generation Dispatch in Power Systems To my Mother and Father Page ii Improved Generation Dispatch in Power Systems ABSTRACT The economic allocation of generation among individual generating sets performed in an En­ ergy Management Centre relies on simple models of power plant behaviour. The plant is re­ garded as a power source which can be varied at will, with some maximum rate of change. However, there are many other relevant power station attributes, which, although clearly re­ cognized, are not explicitly taken in consideration in the Energy Management Centre. Primary control of grid frequency, achieved by governor action, relies on the fact that some generators are operating above the minimum pressure necessary to achieve their dispatched load. The response of such a generator to a frequency deviation from nominal, termed the governor gain, is an automatic control action aimed at reducing supply and demand imbal­ ance and hence containing frequency within limits. The ability of a generating unit to provide active power reserve for frequency regulation is a function of its dispatched load and operating pressure. If this relationship and the associated costs are known then the required reserve can be scheduled in the most economic way over the entire power system by an enhanced dispatch algorithm which includes the operating pressure. The nature of these relationships is examined in this thesis using plant models and tests and a system simulation is presented to test the advantages of the proposals by comparison with the original system. A method of trading reserve provision on thermal plant with other means such as pumped storage, gas turbines and combined cycle plant is discussed. The modes of operation are discussed and it is seen that worthwhile gains in system economics and per­ formance are possible. Page iii Abstract Improved Generation Dispatch in Power Systems ACKNOWLEDGEMENTS I would like to thank my supervisor Dr. R.M. Dunnett for his helpful comments, friendly advice and approachability which gave me confidence and encouragement during my research. I would also like to sincerely thank my group head Dr. J.F. Macqueen for his help and support in steering the project. I would like to express my appreciation to my academic supervisor Dr. M.J. Short and to Mr. E.D. Farmer for their help and comments. I am also indebted to the convenor of WG04 Mr. F.L. Carvalho for his counsel and advice and particularly for making available the opportunity to obtain the plant test data presented throughout this thesis. In addition, I am grateful to all my colleagues on WG04 for the stimu­ lating and lively workshop sessions and the feedback and comment obtained from Dr. F.J McDyer of ESB, Dipl.-lng. H. Kurten of KWU, Si. A. DeMarco of ENEL and Mr. P. Bodach of Ontorio Hydro. Acknowledgements are due for the help of Mr. T. Canning of ESB in performing some of the plant tests reported in this thesis and to Mr. D. O'Connor and Mr. A. Egan for many interesting meetings. A special mention is made of Mr. J. Corr of the North Wall Power Station for his useful suggestions. Similarly, I would like to thank Dr. B. Fox of QUB for his advice and guidance. Finally, my gratitude is shown to all the station staff who helped in performing the tests, my colleagues in the Power Systems Group at NGRDC and in the Electric Energy Systems Section at Imperial College ( who are too numerous to mention individually ) for providing a pleasant working environment. In particular, I would like to thank Mrs. H.M. Chandler for her indispensible assistance. This work was carried out at the National Grid Research and Development Centre and is published by permission of the National Grid Company pic. Page iv Acknowledgements Improved Generation Dispatch in Power Systems Table of Contents 1.0 CHAPTER ONE - INTRODUCTION .................................................................................. 1 1.1 PREAMBLE ................................................................................................................... 1 1.2 PLANT AND SYSTEM INTERFACE ............................................................................... 2 1.2.1. POWER PLANT CONSTRAINTS ............................................................................. 2 1.2.1.1 MAXIMUM AND MINIMUM POWER ................................................................. 2 1.2.1.2 RATE OF CHANGE LIMITATIONS ..................................................................... 2 1.3 PLANT REPRESENTATION IN DISPATCH SYSTEMS .................................................... 2 1.3.1 OBJECTIVE FUNCTION ............................................................................................ 3 1.3.2 PLANT CONSTRAINTS ............................................................................................ 4 1.3.2.1 COAL MILLS .................................................................................................... 4 1.3.2.2 BOILER FEED PUMP ........................................................................................ 4 1.4 CURRENT DISPATCH PRACTICES ............................................................................... 5 1.4.1 U.K. SUPPLY SYSTEM ............................................................................................ 5 1.4.2 IRISH SUPPLY SYSTEM .......................................................................................... 5 1.4.3 ITALIAN SUPPLY SYSTEM ...................................................................................... 5 1.5 ACTIVE POWER RESERVE ............................................................................................ 6 1.5.1 ISLAND SYSTEMS .................................................................................................. 7 1.5.2 FREQUENCY REGULATION .................................................................................... 7 1.6 OVERVIEW OF THESIS .................................................................................................. 8 2.0 CHAPTER TWO - FREQUENCY REGULATION FROM THERMAL PLANT..................... 10 2.1 INTRODUCTION ........................................................................................................... 10 2.2 POWER PLANT MODELLING ...................................................................................... 11 2.2.1 MODEL EQUATIONS ............................................................................................ 11 2.2.1.1 EVAPORATOR ................................................................................................ 11 2.2.1.2 SUPERHEATER .............................................................................................. 13 2.2.1.3 REHEATER ...................................................................................................... 13 2.2.1.4 GENERATED POWER ...................................................................................... 13 2.2.1.5 COMBUSTION SYSTEM ................................................................................. 13 2.2.1.6 GOVERNOR VALVE MODEL ........................................................................... 13 2.2.2 SIMPLIFYING ASSUMPTIONS ............................................................................... 15 2.2.3 PARAMETERS AND SCALING ............................................................................. 16 2.2.4 VARIABLE BOUNDS .............................................................................................. 16 2.3 STATE VARIABLE REPRESENTATION ......................................................................... 17 2.4 STEADY STATES ......................................................................................................... 17 2.5 LINEARIZATION ........................................................................................................... 18 2.6 GOVERNOR GAIN ...................................................................................................... 20 2.7 STEP RESPONSE ......................................................................................................... 21 2.8 GAIN AND ENERGY CALCULATIONS ......................................................................... 22 2.9 CONCLUSIONS ........................................................................................................... 23 3.0 CHAPTER THREE - ACTIVE POWER RESERVE PROVISION COSTS .............. 27 3.1 INTRODUCTION ........................................................................................................... 27 3.2 MODERN POWER STATION PLANT ........................................................................... 27 3.2.1 TURBINE PLANT .................................................................................................. 29 3.2.2 BOILER PLANT .................................................................................................... 29 3.2.3 METHODS OF GOVERNING .................................................................................. 31 3.2.4 THE DESIGN POINT .............................................................................................. 32 3.3 AERODYNAMICS AND THERMODYNAMICS ..............................................................