INVESTIGATION OF HARMONICS EFFECTS IN POWER SYSTEMS AND MITIGATION TECHNIQUES A dissertation submitted to the Department of Electrical Engineering, University of Moratuwa In partial fulfillment of the requirements for the Degree of Master of Engineering By NALLA HANDI DEEPAL WANIGARA TNE Supervised by: 1. Prof. J. R. Lucas 2. Dr. W. M. Wijekoon Department of Electrical Engineering University of Moratuwa, Sri Lanka 2005 85790 Abstract The Electrical power industry is one of the fastest growing industries in the world today. Nowadays electricity consumers are very much concerned of the quality of the supply they receive, due to increased use of sophisticated equipment in their day-to- day activities. Nature of electrical power is such that it can neither be conveniently stored in quantity nor be subjected to quality assurance checks before it is used. As such, study on Power Quality issues in power systems has become one of the most important areas in Electrical Engineering. Among many power quality problems that prevail in power systems, Harmonic distortion continues to cause more and more problems in electrical installations due to proliferation of high power semi conductor devices and power electronics in industrial processes, and microelectronics processors in a wide range of equipment’s. This study investigates the effect of harmonic distortion in the power system and its components. Harmonic current measurements are carried out at number of different consumer installations to determine the harmonic distortion levels and contribution of harmonic distortion to their present problems. Furthermore, harmonic measurements are also carried out on some common non-linear loads and measured harmonic spectrums are compared with theoretical results. The various harmonic mitigation techniques employed in the power system are studied, concentrating on active filters, because it has become the popular choice of many harmonic mitigation equipment manufacturers today. The different active filter control strategies are also studied and their performances are compared with real life applications. A computer model of a shunt active filter is developed and simulated in the MATLAB/SIMULINK environment. It is concluded that the harmonic distortion level at most of the installations are well beyond the accepted international standards and the effects of harmonic distortion are investigated neither by the utility nor by the consumers. Now it is the best time to impose appropriate regulations to limit harmonic emission by individual consumers, which would be beneficial to the utility as well as to the electricity consumers. DECLARATION The work submitted in this dissertation is the result of my own investigation, except where otherwise stated. f It has not already been accepted for any degree, and is also not being concurrently submitted for any other degree. N.J-t[). W,inigaratne Date :l,~j ...... \J :l.Cil) S" We endorse the declaration by the candidate Prof. J .R. Lucas --~ "' ~\ ' , ·""'· Dr. W.M.:-Wij!loon v /~ Acknowledgements There are many individuals who deserve acknowledgement and gratitude for their contribution towards the successful completion of this thesis. First, I gratefully acknowledge my supervisors Professor J. R. Lucas and Dr. W. M. Wijekoon for their valuable guidance and advice, which were immensely useful for this study. It is a remarkable opportunity for me to share their knowledge and expertise in the area of Power Quality in Electrical Engineering. i Also, my special thanks and grateful acknowledgement extends to Professor ll.Y.R. Perera, Head of the Department of Electrical Engineering, University of Moratuwa and his staff of the Department, and course coordinators of the Master of Engineering course for the years 2001/2003, Dr. H.J.C. Peris, Dr. N.K. Wickramarachchi, and Mrs. A.A. Abeygunawardhana for their valuable support in completing this thesis. I am grateful to my employer Ceylon Electricity Board, for granting study leave and financial support for this study. My special thanks also go to colleagues in the Ceylon Electricity Board, Lanka Electricity Company (Pvt) Limited, Lanka Transformers Limited and friends in Master of Engineering 200112p03 batch for their cooperation ".!" extended in completing this thesis. Finally, my very special thanks go to my wife Deepani for her pontinuous encouragement, patience and support during the period I worked on this thesis. None of this would be possible if it were not for the love and support of my wife ~ daughters :. ... Anuradha, Duleena and Raveena. ..;' ~ / IV LIST OF FIGURES Figure 2.1 Balanced three-phase power system 2.2 Harmonic sequences of different harmonic orders 2.3 Current waveform relation-ship in a linear load 2.4 Current waveform relation-ship in a non-linear load 2 5 Harmonic model of a non-linear load 2.6 Harmonic spectrum of a typical CFL 2.7 Harmonic spectrum of a typical SMPS 2.8 Harmonic spectrum of a typical six-pulse bridge 2.9 Voltage and Current for a linear, lagging load j 3.1 Measured Harmonic spectrum of a CFL lighting circuit 3.2 Variation (Measured) of% THDI for a CFL lighting circuit 3.3 Measured Harmonic spectrum of an UPS supplying power to a personal computer. 3.4 Variation (Measured) of%THDl of an UPS supplying power to a personal computer. 3.5 Measured current Harmonic spectrum of an ASD supplying power to a 35kW motor. 3.6 Variation (Measured) of%THDI of an ASD supplyin~;ower to a " 35kW motor 3.7 Variation (Measured) of%THDV of an ASD supplying power to a 35kW motor 3.8 Variation (Measured) of%TIIDI for the three-phase supply to CEB, DGM office Ratmalana. :. .... ., 3. 9 Variation (Measured) of% THO 1 for the neutral conductor of three-phase supply to CEB, DGM office Ratmalana. v Page 09 10 13 13 14 16 16 17 27 35 35 36 37 38 39 ,.. 39 ... 41 42 3. I 0 Measured current Harmonic spectrum for the three- phase supply to CEB, DGM office Ratmalana. 42 3.11 Variation (Measured) of%THDI for the three-phase supply to Branch Manager's Office LECO- Kalutara 3.12 Variation (Measured) of%THDV for the three-phase supply to Branch Manager's Office LECO- Kalutara 4.1 A series passive filter 4.2 A shunt passive filter 4.3 Series Passive AC Input Reactors 4.4 Components of shunt active filter 4.5 Compensation characteristics of a shunt active filter j 44 44 49 50 51 53 56 4.6 Series Active Filter 57 4.7 (a) Combination of shunt active filter and shunt passive filter 59 4.7 (b) Combination of series active fi Iter and series passive filter 59 4. 7 (c) Series active filter connected in series with shunt passive filter 59 4.8 Zig-Zag transformer application as third harmonic filter 60 4.9 Cancellation of 5th and 7th harmonic currents by using 30° phase-shifted transformer connection 61 5. I Block diagram of an active filter using notch filtering for harmonic detection 65 5.2 Block diagram of IRPT based active power filter controller 68 5.3 Block diagram of an active power filter with (SRF), based controller 69 5.4 Block diagram of an active filter controller using Sinusoidal Subtraction for harmonic detection --~ "' 5.5 (a) One cycle (20 ms) of input waveform with 40 samples 5.5 (b) The FFT output 5.6 PWM control of voltage-fed inverters 5.7 MATLAB/SIMULTNK model of a shunt Active Filter 5.8 Block diagram, of the Controls and Gating Signal Generator model .... _ ..,r 5.9 Simulation Result: The Wave form and the spectrum of the current drawn by a three-phase Rectifier feeding SOkW, load. VI . ;'. 70 71 , . 72 76 78 ·~ · 79 /~ 81 5.10 Simulation Results, Per phase Load current, Source current and harmonic current with shunt Active Filter in action. 82 5.11 Simulation Result: The Wave form and the spectrum of the source current, with the Active Filter in action 83 5.12 Simulation Result: The Wave form and the spectrum of the per phase Harmonic Component, extracted from load current using Notch Filter 84 I .. ;- " Vll ~· .. .., ' . ; '. ·~ · /~ LIST OF TABLES Table 2.1 Spectral components of waveforms 2.2 Harmonic order V s Phase Sequence 2.3 Harmonic limits for utility 2.4 Harmonic limits for customers 4.1 Advantages and Disadvantages of series passive harmonic filter. 4.2 Advantages and Disadvantages of shunt passive harmonic filter 4.3 Advantages and Disadvantages of Series Passive AC Input Reactors 4.4 Comparison between Shunt and Series Active Filters i 4.5 Comparison of hybrid filter topologies 5.1 Summary of the performance of harmonic determination methods 5.2 Comparison of the properties of Load current with and without the Active Filter compensation. .. ~ " VIII ';..AI .. v .¥: v~ · Page 08 11 31 31 50 51 52 57 58 74 84 /~ LIST OF ABBREVIATIONS AND PRINCIPLE SYMBOLS ABBREVIATIONS AC ANSI ASD CEB CFL DC FFT HV IEC IEEE IFFT IGBT IHD IL IRPT ISC LECO LV MCB MV PCC PWM RCCB RMS SMPS SRF T DD THDI - Alternating Current - American National Standard Institute -Adjustable Speed Drive - Ceylon Electricity Board -Compact Fluorescent Lamp - Direct Current - Fast Fourier Transform - High Voltage i - International Electromechanical Commission - Institute of Electrical and Electronics Engineers - Inverse Fast Fourier Transform - Insulated-Gate Bipolar Transistor - Individual Harmonic Distortion -Maximum Demand Load Current - Instantaneous Reactive Power Theory - Maximum Short Circuit Current - Lanka Electricity COmpany -Low Voltage -Miniature Circuit Breaker - Medium Voltage ".t-' - Point of Common Coupling -Pulse Width Modulation , - Residual Current Circuit Breakers y , - Route Mean Square - Switch Mode Power Supplies ·~ , -=-·- - Synchronous Reference Frame v /~ -Total Demand Distortion -Total Harmonic Distortion-current lX THDV UPS VSI PRINCIPLE SYMBOLS -Total Harmonic Distortion-voltage - Un-interruptible Power Supply -Voltage Source Inverter A - Ampere Fr - power factor Fptot - True power factor F p disp - Displacement power factor F p dist - Distortion power factor j I - Current H -Henry v - Voltage p - Active power f - frequency fo _cut-off frequency f, - fundamental frequency h - Harmonic number kVA - kilo volt ampere kV - kilo volt kW -kilo watt "/ ... (l) - Angular velocity X :. .... "' , .. ,.~ . ·~ · ,.~ Declaration Abstract Dedication Acknowledgement List of Figures List of Tables CONTENTS List of abbreviations and principle symbols Chapters 1. Introduction 1.1 Motivation 1.2 Objectives-Scope of the project. 1.3 Overview of the Thesis 2. Harmonics in power systems 2.0 What are power system harmonics? 2.1 Harmonic Number 2.2 Odd and Even order Harmonics 2.3 Inter Harmonics 2.4 Harmonic Sequence 2.5 Individual and Total Harmonic Distortion 2.6 The Crest Factor ... ~ " 2.7 How Harmonics are generated in power systems 2.8 Harmonics generating loads in power systems 2.8.1 Single phase harmonics generating loads 2.8.2 Harmonics generating three phase loads 2.9 Effects of harmonics on power system components 2.9.1 Transformers 2.9.2 Cables 2.9.3 Neutral conductors XI l :..a .... .,; , ; ' 11 lll IV v Vlll IX 01 03 04 04 06 07 07 07 08 1 1 12 12 15 15 17 .. ~ . 18 18 20 20 2.9.4 Power factor correction capacitor banks 22 2.9.5 AC Induction motors 22 2.9.6 Circuit Breakers and Relays 23 2.9.7 Bus ways 24 2.9.8 Measuring instruments 24 2.9.8.1 The consequences of under measurements 25 2.10 Effects of harmonics on the system voltage. 26 2.11 Effects of Harmonics on System Power Factor 27 2.12 Harmonics Standards 29 2.12.1 IEEE 519-1992 Harmonics Limit for Utility 31 2.12.2 IEEE 519-1992 Harmonics Limit for Custo~rs 31 3. Harmonics Measurements at selected consumer Installations 3.0 Introduction 33 3.1 Instruments used for Harmonic Measurements 33 3.2 Sites Selected for Measurements 34 3.2.1 Harmonic Measurements at individual loads 34 3.2.l.l.Harmonics Measurements in a Lighting Sub circuit with only Compact Fluorescent Lamps (CFL) 34 3.2.1.2.Harmonics Measurements in a UPS delivering power to a personal computer. 3.2.1.3.Harmonics Measurements in an Adjustable Speed Drive (ASD) .. ;, " 3 .2.2 Harmonic Measurements at Electrical Installations 3.2.2.l.Harmonic Measurement at, Deputy General Manager's Office Ceylon Electricity Board Ratmalana. . . ;~. 3.2.2.2.Harmonic Measurement at, Branch Manager's Office of Lanka Electricity Company (Pvt) Lj{llit~ · 36 37 40 40 (LECO), Kalutara v 43 3.2.2.3 Harmonic Measurement at Hotel Blue Water / Wadduwa 45 3 .2.2.4 Harmonic Measurement at Hotel Mount Lavenia 45 Xll 4. Harmonic Mitigation Techniques 4.1 Harmonic Filtration 4.1.1 Passive Harmonic Filters 4.1.1.1 Series Passive Harmoruc Filters 4.1.1.2 Shunt Passive Harmonic Filters 4.1.1.3 Series Passive AC Input Reactors 4.1.2 Active Harmonic Filters 4.1.2.1 Classification of Active Harmonic Filters 4.1.2.2 Shunt Active Harmonic Filters 4.1.2.3 Series Active Harmonic Filters j 4.1.2.4 Hybrid Active/Passive Harmonic Filters 4.2 Harmonic Current Cancellation 4.3 Equipment Design 5. Computer modeling, simulation and control of Active filters 5.0 Introduction 5.1 Control strategies for Active filters 5.1.1 Harmonic Determination by Notch Filtering 5.1.2 Harmonic Determination by Instantaneous Reactive Power Theory (IRPT) 5.1.3 Harmonic Determination by Synchronous Reference Frame (SRF) method --~ .. 5.1.4 Harmonic Determination by Sinusoidal Subtraction 47 47 48 49 50 51 52 54 55 56 57 60 61 63 64 65 66 68 70 5.1.5 Harmonic Determination by Fast Fourier Transform (FFT). , 70 ...... . 5 .1.6 Performance Comparison of Harmonic Detection Methods Under Practical Conditions 73 vAt. · -:... 74 5.2 The out put current controller for Active filters v 5.2.1Active Filter current control using Voltage-fed PWM invertersri5 5.3 The Interface Filter of the Active filters 5.4 Computer Modeling and Simulation of Active filters XIII 76 76 5.4.1 Model ofthe Power Source 5.4.2 Model of the Non-linear Load 5.4.3 Model of the Controls and Gating Signal Generator 5.4.4 Model ofthe PWM Inverter 5.4.5 Model of the Interface Filter 5.4.6 Model of the Coupling Transformer 5.5 Simulation Results 6.Coclusions and Recommendations 6.1 Conclusions 6.2 Recommendations 6.3 Future works References Appendices Appendix 1 Site measurement data Appendix 2 l Parameters of MA TLAB/SIMULINK computer model Appendix 3 Specifications of measuring instruments. "~ ... XIV ., ... v 77 77 79 79 80 80 80 , . ; ' . .... 85 86 86 87 ~ /