University of Wollongong Research Online University of Wollongong Thesis Collection University of Wollongong Thesis Collections 1994 Harmonic management of transmission and distribution systems Maty Ghezelayagh University of Wollongong Recommended Citation Ghezelayagh, Maty, Harmonic management of transmission and distribution systems, Doctor of Philosophy thesis, Department of Electrical and Computer Engineering, University of Wollongong, 1994. http://ro.uow.edu.au/theses/1343 Research Online is the open access institutional repository for the University of Wollongong. For further information contact Manager Repository Services: [email protected]. HARMONIC MANAGEMENT OF TRANSMISSION AND DISTRIBUTION SYSTEMS A thesis submitted for the award of the degree DOCTOR OF PHILOSOPHY from UNIVERSITY OF WOLLONGONG BY M. GHEZELAYAGH, B.Sc, M.Sc in Electrical Engineering UK!V5Rr;iV'Gr WOUC,\"3O::G LI- --Y Department of Electrical and Computer Engineering 1994 ABSTRACT HARMONIC MANAGEMENT OF TRANSMISSION AND DISTRIBUTION SYSTEMS This thesis is concerned with some important aspects of harmonic management in a multi-voltage level power system including transmission, sub-transmission and distribution levels. In the work presented both deterministic and statistical approaches for harmonic analysis have been used. Investigations have been made both in Time and Frequency Domains. An already available computer simulation program in Time Domain has been used to derive frequency domain models of distribution feeders with composite loads. A Frequency Domain computer program has been modified to give the statistical data of harmonic voltage distortion levels of a large power system. The thesis examines some of the fundamental assumptions used in harmonic analysis with the aid of a Time Domain simulation program. In harmonic analysis two of the commonly made assumptions are: (i) harmonic sources are represented with ideal ac current sources having equal phase angles, (ii) non-distorting loads are represented with constant impedances. The thesis also discusses the harmonic current distortion level of distribution feeders with different load categories (e.g., residential, commercial and industrial) based on measurements data. This data is used for modelling of harmonic sources in Frequency Domain computer program. The major harmonic management questions addressed in this thesis are: (i) setting of limits for harmonic voltage distortion at different voltage levels, and (ii) the determination of the maximum permissible sizes of several new distorting loads. Existing harmonic standards give a different limit for each voltage level. If these limits are not well co-ordinated then there will be unnecessary restrictions on harmonic injection by distorting loads. A computer-based technique which can be used to investigate this problem has been developed. The approach is statistical in nature and it accounts for variations in the Space Domain (at different busbars in the system), the Time Domain (with different capacitor connections and line outages) and combinations of both Time/Space Domain. Variation of the statistical data with respect to the voltage level is investigated and the suitability of the 95% confidence level for assessment of the harmonic voltage distortion level at each voltage level is discussed. In addition, the probability distribution as affected by the strength of the power system is investigated. Histograms and probability distribution curves are used to find the best statistics for describing the harmonic voltage distribution. The effect of distorting loads in different parts of a power system on the harmonic distortion levels in a particular subsystem is also investigated. With existing harmonic management techniques, there is no guarantee that, after connection of a new distorting load, the harmonic voltage distortion level remains within limits at all voltage levels. On the other hand there is no method to determine the permissible size of several new distorting loads which can be connected at different voltage levels and locations simultaneously. Two techniques which use constrained and unconstrained non-linear optimization program have been developed to overcome the above restrictions. These techniques have been applied to a typical power system to demonstrate their application. The effect of non-distorting loads and system capacitance is discussed. The effect of the harmonic voltage limit at different voltage levels on the maximum permissible harmonic current injection is also investigated. DECLARATION This is to certify that the work reported in this thesis has been performed by the author unless specified otherwise. No part of it has been submitted as a thesis to any other university Maty Ghezelayagh ACKNOWLEDGMENTS I would like to express my thanks to my supervisors Associate Prof. V.J. Gosbell and Dr. Don Geddey of the Pacific Power Company for their encouragement and guidance throughout this work. Thanks also to my colleagues for their helpful technical discussions. I am also very grateful of both Australian Postgraduate Research Awards Scheme and the Pacific Power Company of NSW for their financial support. Contents ents Introduction 1 Overview of Harmonics in Power Systems 1 Computer Techniques for Harmonic Analysis 4 1.2.1 Deterministic Techniques 4 1.2.1 Probabilistic Techniques 7 Harmonic Modelling of Power System Equipment 8 Harmonic Standards 11 1.4.1 IEEE Standard 12 1.4.2 Australian Standard 12 1.4.3 IEC Standard 13 Harmonic Management in Power Systems 16 1.5.1 New Zealand Standard 17 1.5.2 Australian Standard 18 1.5.3 IEEE Standard 18 1.5.4 IEC Standard 19 The Objectives and Contributions of the Thesis 21 Plan of the Thesis 23 Chapter 2. Application of Power Electronic Simulator for Time Domain Analysis of Distribution Network Harmonics 29 2.1 Introduction 29 2.2 Device and Circuit Models 31 2.3 Accuracy of PES Device Models 31 2.3.1 Six Pulse Rectifier 32 2.3.1.1 Accuracy Control for Integration 39 2.3.1.2 Computation Time 39 2.4.1 Three Phase Two Pole Induction Motor 40 2.4.1.1 Computation Time and Accuracy Control of Integration for Motor Simulation 42 2.5 Conclusions 42 Chapter 3. Interaction Between Harmonic Sources and Power System Components 44 3.1 Introduction 44 3.2 Interaction Between Harmonic Sources and Different 46 Load Categories 3.3 The Effect of Power System Modelling on Harmonic Propagation 57 3.4 Effects of Load Composition 65 3.5 Conclusions 69 Chapter 4. Harmonic Modelling of Distribution Feeders 71 4.1 Introduction 71 4.2 Harmonic Modelling of Distribution Feeders 73 4.3 Study Example 77 4.3.1 Model 1: Harmonic Current Source in Parallel with Impedance 77 4.3.2 Model 2: Ideal Harmonic Current Source 80 4.4 General Equation for Harmonic Modelling 82 4.5 Conclusions 84 Chapter 5. Accuracy of Representation of Harmonic Sources with Ideal Current Sources and Equal Phase Angles 86 5.1 Introduction 86 5.2. Loads on One Distribution Feeder 88 5.3 Study Example 93 5.4 Modelling of Distribution Feeders in Different Subsystems 95 5.5 Conclusions 98 Chapter 6. Propagation of Harmonics in a Multi Voltage Level Power System 100 6.1 Introduction 100 6.2 Effect of System Parameters on Harmonic Voltage Level 101 6.3 Description of Study System 103 6.4 Harmonic Propagation 104 6.5 Effect of Subsystem Structure on Harmonic Propagation 112 6.6 Calculation of Equivalent Harmonic System Impedance 113 6.6.1 Effect of Network Parameter Changes on Impedance 115 6.7 Conclusions 116 Chapter 7. Harmonic Current Distortion Level of the Distribution Feeders 121 7.1 Introduction 121 7.2 Basic Definitions of Harmonic Distortion 122 7.3 Survey of Harmonic Measurements 124 7.3.1 Summary of Harmonic Current Distortion Level as Measured by Different Utilities 135 7.4 Conclusions 136 Chapter 8. Statistical Assessment of the Harmonic Voltage Distortion Level in a Large Power System. (Part I, Variation of the Harmonic Voltage Distortion Level Within a Subsystem) 137 8.1 Introduction 137 8.2 Computer Program 142 8.3 Description of the Study System and Modelling of Harmonic Sources 144 8.4 Application of Statistical Techniques in Time and Space Domain 145 8.5 Effect of the Line Outages and Capacitor Combination on the Harmonic Distortion Level 161 8.5.1 Time Domain 161 8.5.2 Time/Space Domain 162 Comparison Between Statistical Data in Space, Time and Space/Time Domain 163 Statistical Data for the 7th Harmonic 163 Sensitivity Analysis With Respect to Load Category and Individual Harmonic Current Distortion Level 165 Conclusions 169 Statistical Assessment of the Harmonic Voltage Distortion Level in a Large Power System. (Part II, Variation of the Statistical Data Between Different Subsystems) 172 Introduction 172 Variation of the Statistical Data Between Different Subsystems 174 Effect of the Strength of the Subsystem on Harmonic Voltage Distortion Levels 190 Comparison Between Peak and Light Load Condition 192 Harmonic Voltage Distortion Level at the Load Points in Transmission System (330 KV) 194 Effects of the Various Distorting Loads to Harmonic Voltage Distortion Level 196 Ratio of Harmonic Voltage Distortion Level With Respect to Limits 200 Conclusions 202 Maximum Permissible Harmonic Current Injection (Part I, Unconstrained Current) 208 10.1 Introduction 208 10.2 Permissible Harmonic Current Injection Level 211 10.3 Application of the Proposed Technique on an Example System 212 10.4 Comparison Between Cases 215 10.5 Effect of Harmonic Voltage Limit on the Permissible Harmonic Current Injection 217 10.6 Conclusions 220 Chapter 11. Maximum Permissible Harmonic Current Injection (Part II, Constrained Current) 223 11.1 Introduction 223 11.2 Mathematical Equations for Constrained Non-Linear Maximization Program 224 11.3 System Studies 226 11.3.1 Constrained Current 227 11.3.2 Unconstrained Current 230 11.4 Effect of HV and LV Filters on the Permissible Harmonic Current Injection Level 232 11.5 Effect of Harmonic Voltage Limit on the Permissible Harmonic Current Injection 233 11.6 Future Work 236 11.7 Conclusions 237 Chapter 12.