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Analysis of an Induction Regulator for Power Flow Control in Electric Power Transmission Systems

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Analysis of an Induction Regulator for Power Flow Control in Electric Power Transmission Systems Examensarbete Analysis of an induction regulator for power flow control in electric power transmission systems Anna Guldbrand LITH-IFM-EX--05/1543--SE Department of Physics and Measurement technologies Analysis of an induction regulator for power flow control in electric power transmission systems Masters Thesis Anna Guldbrand Supervisor: Stefan Johansson, ABB Corporate Research, Västerås Examiner: Sven Stafström, IFM, Linköpings universitet Avdelning, Institution Datum 051216 Division, Department Date Theory and Modelling Department of Physics, Chemistry and Biology Linköpings universitet, SE-581 83 Linköping, Sweden Språk Rapporttyp ISBN Language Report category __________________________________________________ ISRN____ LITH-IFM-EX—05/1543--SE Svenska/Swedish Licentiatavhandling ______________________________________________ x Engelska/English x Examensarbete C-uppsats D-uppsats Serietitel och serienummer ISSN ________________ Övrig rapport Title of series, numbering _______________ URL för elektronisk version http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5329 Titel Analysis of an induction regulator for power flow control in electric power transmission systems Title Författare Anna Guldbrand Author Sammanfattning Abstract Controlling the power flow in transmission systems has recently gained increased interest. The difficulties of building new lines and the pressure of having a high utilization of existing assets, makes the flexibility of grid systems increasingly important. This master thesis work investigates induction regulators as control devices for active power flow in a transmission system. A small change in angle of the rotor affects both the amplitude and the phase of the voltage. The magnetic coupling in the induction regulator can be controlled by changing the permeability of a thermo magnetic material such as gadolinium and can hence give a second independent controlling parameter. An analytical model and calculations in the FEM software AceTripleC together with Matlab, is used to simulate the influence of the regulators connected to a simple grid in case1, a 400 kV scenario and case 2, a 45 kV scenario. The analysis was carried out on a small transmission system consisting of two parallel transmission lines connected to source and load. The induction regulators are connected to one of the parallel transmission lines. The regulators modelled in case 1 must be able to control the active power flow in the regulated line to vary between 50 and 150 % of the original power flow through this line. This shall be done over a range of 0 to 800 MW transmitted power. The regulators modelled in case 2 must be able to control the active power flow in the regulated line to vary between 0 and 30 MW, if this does not cause the power flow in the parallel line to exceed 30 MW. This shall be done over a range of 0 to 50 MW transmitted power. The regulators are designed as small and inexpensive as possible while still fulfilling requirements regarding the active power flow controllability in the grid, current density in windings and maximum flux density in core and gap. The results indicate that the size of the 400 kV solution has to be reduced to become competitive whereas for the 45 kV solution the relative difference to existing solution is smaller. Advantages with the proposed design over a phase shifting transformer are mainly a simpler winding scheme and the absence of a tap changer. Nyckelord Power flow control, Phase shifting, Induction regulator, Gadolinium Keyword Acknowledgement I would like to thank my supervisor Stefan Johansson at ABB Corporate Research, for all encouraging and help. I would also like to thank Gunnar Russberg for the help and enthusiasm he provided, my examiner Sven Stafström and my opponent Johan Gunnar for putting time and effort into reading my report and give me valuable advice. Also thanks to Micke, Erik, Johan, Agneta and the rest of the staff at the department, for making my time at ABB CRC-PT in Västerås a pleasant experience. Last but not least, thanks to my friends in Linköping, even “tentaplugg” is pure joy with you! Summary Controlling the power flow in transmission systems has recently gained increased interest. The difficulties of building new lines and the pressure of having a high utilization of existing assets, makes the flexibility of grid systems increasingly important. This master thesis work investigates induction regulators as control devices for active power flow in a transmission system. A small change in angle of the rotor affects both the amplitude and the phase of the voltage. The magnetic coupling in the induction regulator can be controlled by changing the permeability of a thermo magnetic material such as gadolinium and can hence give a second independent controlling parameter. An analytical model and calculations in the FEM software AceTripleC together with Matlab, is used to simulate the influence of the regulators connected to a simple grid in case1, a 400 kV scenario and case 2, a 45 kV scenario. The analysis was carried out on a small transmission system consisting of two parallel transmission lines connected to source and load. The induction regulators are connected to one of the parallel transmission lines. The regulators modelled in case 1 must be able to control the active power flow in the regulated line to vary between 50 and 150 % of the original power flow through this line. This shall be done over a range of 0 to 800 MW transmitted power. The regulators modelled in case 2 must be able to control the active power flow in the regulated line to vary between 0 and 30 MW, if this does not cause the power flow in the parallel line to exceed 30 MW. This shall be done over a range of 0 to 50 MW transmitted power. The regulators are designed as small and inexpensive as possible while still fulfilling requirements regarding the active power flow controllability in the grid, current density in windings and maximum flux density in core and gap. The results indicate that the size of the 400 kV solution has to be reduced to become competitive whereas for the 45 kV solution the relative difference to existing solution is smaller. Advantages with the proposed design over a phase shifting transformer are mainly a simpler winding scheme and the absence of a tap changer. Keywords: Power flow control, Phase shifting, Induction regulator, Gadolinium TABLE OF CONTENTS 1 INTRODUCTION 11 1.1 PURPOSE AND SCOPE 11 1.2 DEFINITIONS 12 2 PROBLEM DESCRIPTION 15 2.1 MOTIVATION OF THE STUDY 15 3 BACKGROUND 19 3.1 INDUCTION REGULATOR 19 3.2 POWER SYSTEM 21 3.2.1 Limits to the loading capability 23 3.2.2 Surge impedance loading and PV curve 23 3.2.3 Transmission matrix 24 3.3 PERMEABILITY 25 3.4 THE THREE PHASE INDUCTION MACHINE 26 3.4.1 Induced magnetic flux density 26 3.4.2 Induced voltages 28 3.4.3 Leakage flux 30 4 METHODS 33 4.1 GRID MODEL CALCULATED IN MATLAB 33 4.2 SIMULATIONS 34 4.2.1 Electromagnetic simulations 34 4.2.2 Induction regulator geometry 34 4.2.3 Analytical model 37 5 CONCEPT 41 5.1 THERMO MAGNETIC MATERIAL 41 5.2 MOTORFORMER 42 5.3 CONNECTIONS 44 6 CASE 1 47 6.1 REQUIREMENTS 47 6.1.1 Varying permeability 50 6.1.2 Parameters and initial values 50 6.2 RESULTS 51 6.2.1 Reducing the variable parameters 51 6.2.2 Maximum magnetic flux density 52 6.2.3 Optimization when NA = 250 56 6.2.4 Optimization when NA = 350 60 6.2.5 Reactive power 62 6.3 DISCUSSION 63 7 CASE 2 67 7.1 REQUIREMENTS 67 7.2 RESULTS 68 7.2.1 Active and reactive power flow 68 7.2.2 Optimization 70 7.3 DISCUSSION 72 8 CONCLUSIONS 73 9 FUTURE WORK 75 10 REFERENCES 77 11 APPENDIX A MATLAB FIGURES 79 11 1 Introduction 1.1 Purpose and scope The purpose of this report is to look into the possible use of an induction regulator when controlling active power flow in transmission systems. This report describes a model of a modified induction regulator to control the power flow in a simple transmission system. The regulator described in this report is based upon an induction machine used for voltage regulation in normal cases. An induction regulator is a device where neither stator nor rotor rotates. The magnetic flux density produced by the primary winding induces a voltage in the secondary winding. The phase of the induced voltage can be controlled by shifting the secondary winding relatively the primary winding. The magnetic coupling in the induction regulator is controlled with a thermal magnetic material such as gadolinium. In the thesis work the following question shall be answered: What is the smallest rating the regulator can have and still fulfil the set of requirements stated in the report? It is evaluated towards a simple transmission system consisting of two parallel lines. The work done here does probably not find the optimal regulator. The size is minimized on the basis of the simplified models and programs used. A more thorough design will fine-tune the design further. The result will be used to decide whether to investigate this regulator further or not. A patent regarding this machine and the intended use of it has been applied for. 12 1.2 Definitions T&D Transmission and distribution S Complex power flow P Active power flow Q Reactive power flow U Voltage I Current Source Denotes generated quantity Load Denotes consumed quantity ∆δ Voltage phase shift PST Phase shifting transformer DC Direct current AC Alternating current B Magnetic flux density φ Magnetic flux ϕ Denotes rotation angle of the regulator i Current, complex form u Voltage, complex form Driving voltage U1 -U 2 , gives rise to
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