ANALYSING OF POWER QUALITY PROBLEMS OF WIND POWER GENERATORS By M. L. A. A. Chandranath This thesis was submitted to the Department of Electrical Engineering of the University of Moratuwa in partial fulfillment of the requirements for the Degree of Master of Engineering Supervised By: Dr. D. P. N. Nanayakkara Department of Electrical Engineering University of Moratuwa Sri Lanka 2004 82485 Abstract Wind power as a rule does not contribute to voltage in grids. Also, wind power very often is a source of voltage fluctuations and flicker. Furthermore, care must be taken to upkeep availability of networks more or less dependent on wind power by preventing the voltage from collapsing in conjunction with faults occurring in the grid. The first wind power plant installed at Hambantota III Sri Lanka, 3MW was commissioned in early 1999. Alternating current transmission will turn out to be an economically and technically attractive option in many cases, and dynamic reactive power compensation will then be a natural part of the scheme. The dominating kind of wind power generators are asynchronous, this since they are robust and cost effective. Induction generators, however, do not contribute regulation of grid voltage nor frequency, and they are substantial absorbers of reactive power. Ideally, they need to be connected to very stiff grids in order not to influence power quality is a detrimental way. This is not the case in reality. Quite 0 n the contrary, wind power is usually connected for out in the grid, on sub transmission or distribution levels. The majority cases are 10-40kV. The objective of the research is to analyze the problem of voltage and current harmonics, transient behavior, power fluctuation and reactive power consumption of wind power generators and modeling of wind turbines connected to the medium voltage distribution line of the grid wher~ the other consumers are connected. Often, Voltage regulation problems arise as a consequence of grids being made dependent on wind power, a matter of growing concern as wind power gets more important in the power balance. To certain degree, Voltage Control problems cased by defect of reactive power in the grid can be, and is remedied by installation of fixed or mechanically switched shunt capacitors. This will 'not help on voltage fluctuations, however caused by varying output of wind generators. Regular voltage flicker is part of the picture, as well, caused by such phenomena as turbulent wind impact and so-called tower shadow effects. DECLARATION I hereby declare that this submission is my own work and that, to the best of my knowledge and behalf, it contains no material previously published or written by another person nor material, which to substantial extent, has been accepted fort he award of any other academic qualification of an university or institute of higher learning except where acknowledgment is made in the text. ~_() -MOL.A.A. Chandranath PE/EE/01/99 December 2004 i)/01~ DrODOPONONanayakkara Project Supervisor J/ 0 J 0 0 0 0 December 2004 / ...... .. ~""" --- Acknowledgments I am most grateful and privileged to have Dr.D.P.N. Nanayakkara, Senior Lecturer, University of Moratuwa and Eng. W.N.Jayalath, Electrical Engineer, Ceylon Electricity Board as supervisors. Their kind and encouraging assistance with regard to the problem formulation, construction and comments on the results is greatly appreciated. I am deeply indebted to all the lecturers, colleagues and friends, too numerous to mention here, who have contributed so generously in various stages of this project over few months. ./ Many thanks are owed especially to the Head and the Staff of the Department of Electrical Engineering University of Moratuwa, Colleagues of the batch of the M.Eng/PG Diploma Course in Electrical Engineering, technical staff of the machine laboratory of the Department of Electrical Engineering University of Moratuwa and non executive staff of the computer section of CEB for assistance in reviewing, complying and editing this report. Finally this work is dedicated to my beloved parents and to my wife who have always been with me in every hurdle I cleared. M.L.A.A. Chandranath December 2004 --- ......... ... :-.. CONTENTS ACRONYMS 1 INTRODUCTION 1.1 The Project 1.2 Power Quality Study 1.3 Power Quality 1.4 Power Quality Measures 1.4.1 Reactive Power consumption and Power Factor 1.4.2 Voltage Variations 1.4.3 Flicker 1.4.4 Harmonics 1.4.5 Transient Effects ./ 0 1 1 1 1 2 4 4 5 6 6 1.5 Description of the Host Grid and Wind Turbines 7 1.6 Wind Turbine Technical Specifications 8 2 FUNDAMENTALS OF WIND ENERGY CONVERSION 9 2.1 Fundamentals of wind energy conversion 9 2.2 Turbulence 11 ' 2.3 Wake Effect 11 ---2.4 Energy Calculation 12 --.. 3 POWER FACTOR AND REACTIVE POWER 13 3.1 Power Factor and Reactive Power Requirement 13 3.2 Results for the Total Farm l3 3.3 Results for a Single Wind Turbine (WTG No 4) 15 3.4 4 4.1 4.2 4.3 4.4 Comments on Power Factor and Reactive Power Requirement ANALYSIS OF WIND DATA Statistical Analysis Diurnal Wind Pattern in different monsoon Roughness Mathematical Description of Wind Regimes 4.4.1 Calculation of Weibull Shape Factor 4.4.2 Weibull Shape Factor 5 POWER VARIATIONS 5.1 Power Variation Effects 5.2 Results of Measurement 5.3 Comments on the Power Variations 6 WIND TURBINE MODELING 6.1 Importance of Modeling ./ 6.2 Wind Turbine Models For Present And Future Technologies 6.2.1 Wind Speed Generation Functions 6.2.2 Aerodynamic Power Control 6.2.3.1 Fixed Speed Generator 6.2.3.2 Models of Variable Speed System Turbine (Stator Circuits) 6,2.3.3 Models of Variable Speed Syste!!l Turbine (Rotor Circuits) 6.3 6.4 DFIG Machine Model With The Converter New Trends in Wind Power Generation 6.4.1 Doubly Fed Induction Generator 6.4.1.1 Main Advantages of Doubly Fed Induction Generator 6.4.2 Wind Diesel Hybrid Generation System :-. 17 20 20 22 24 26 27 27 30 30 30 31 36 36 37 37 37 39 40 41 42 44 44 45 45 7 TRANSIENT BEHAVIOUR 47 7.1 Transients During Switching 47 7.2 Cut in at Cut in Wind 47 7.3 Cut in at rated wind speed 49 7.4 Switching in of Capacitive Compensation unit. so 7.5 Service cut out at rated Power 51 7.6 Emergency cut out at rated Power 52 7.7 Comments on Transient Behavior of Wind Machines 53 I 7.8 Harmonic Penetration at Cut in Process 54 8 HARMONICS 56 8.1 Voltage Harmonics: Total Harmonic Distortion 56 8.2 Voltage Harmonic Components 58 8.3 Comments on Voltage Harmonics 59 8.4 Current Harmonics 60 9 CONCLUSION AND RECOMMENDATIONS 61 9.1 Recommendations for Grid Connection of Wind Farm 62 9.2 Recommendations for Wind Turbines 63 9.3 Operation and Maintenance . 63 REFERENCES 64 -- ACRONYMS CEB - Ceylon Electricity Board cov - Coefficient of Variability kV - Ki lo Volt MW - Mega Watt ./ WTG - Wind Turbine Generator kA - Ki lo Ampere MVA - Mega Volt Ampere KVAr - Kilo Volt Ampere Reactive KW - Kilo Watt RMS - Root Mean Square THD - Total Harmonic Distortion XLPE - Cross Linked Poly Ethylene rn!s - Meters Per Second . .._. --- 0