INVESTIGATION OF PARAMETERS OF A STAND ALONE POWER GENERATING SYSTEM, USING AN INDUCTION MACHINE IN SINGLE- PHASE GENERATOR MODE By N.G.D. Wijesiiiwardene 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 in Electrical Engineering. Department of Electrical Engineering Faculty of Engineering University of Moratuwa Sri Lanka December 2003 Abstract In Sri Lanka only around 35% of rural population has reached grid electricity. Therefore stand alone power generation systems will be a major option to provide electricity to rural population as we are rich with hydro resources. In rural electrification, even though DC generators and synchronous generators are used, induction generator has become common in use due to more convenient features like ready availability, simplicity, reliability and robustness. Now the single-phase power with a three- phase induction machine has become an economical options to generate power in stand- alone power generating systems. It is now widely used in Pico scale stand alone power generating systems in Sri Lanka. When a three- phase induction motor is used as a generator in single- phase mode, it should be designed to operate near the best operating point, to provide maximum power output and minimum unbalance. Literatures on this area of subject and published test results are few; manufactures of motors rarely show an interest to measure and publish test res ults of their standard machines in generator mode [2], In this situation it is difficult to find data in this type of generators installed in this country also. It was seen that to find and analyze data of stand alone power generating systems and to study about its parameters will be useful due to the poor availability of literature in this area. Also according to the investigations made, many Pico scale hydro developers seems not paid due attention on whether their plants operate at optimum power out put at minimum unbalance. This study was basically focused to investigate the parameters of a stand alone single phase power generating system using a three phase induction generator to find the system behavior, specially at minimum unbalance with a maximum power output. The study also includes the analysis of the system to find the behavior of the total( generating and distribution) system. II 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 for the /ard of any other academic qualification of an university or institute of higher learning except where acknowledgment is made in the text. N LU·f'.Si ,./\_(_J ~ N G D Wijesiriwardene December 2003 ~ Dr. J.P. Karunadasa Project Supervisor December 2003 ...,; ITEM DECLARATION .\BSTRACT CONTENTS LIST OF TABLES LIST OF FIGURES ACKNOLEDGEMENT CONTENTS CHAPTER I RESEARCH PROBLEM BEING ANAL Y7,ED 1.1 Introduction 1.2 Overview of small scale power generation 1.2.1 Background of small-scale generation in Sri Lanka 1.2.1.1 1.2.1.2 .. Village hydro projects Present & future planning, excursion for rural j PAGE NO. II III VII VIII XI 2 2 2 electrification in Pico scale micro hydro projects 3 1.3 1.4 1.2.2.1 1.2.2.2 Present status in Pico llydro projects Future planning & excursion Research problem at the scene Objective of the study CHAPTER 2 THEORETICAL ANAL YSlS 2.1 Working principle of an induction machine 2.2 Induction machine in generator mode 2.2.1 Effect of saturation Ill 3 5 7 7 8 10 10 2.2.2 The self excited generator 2.2.3 The problem of voltage & frequency contro l of induction in isolated generator operation 2.3 Torque speed characteristics 2.4 The circle diagram 2.5 Induction generators in conjunction with a load controller 2.5.1 Conjunction with a Load Controller ? ~? _,),_ Reactive power control 2.6 Single- Phase output from a Three -Phase Machine 2.6.1 Balancing the single phase load over the three phases of the Induction generators in the C-2C connection j CHAPTER 3 LITERATURE SURVEY 3.1 Induction generator controllers 3.1.1 Fixed and variable load system. 3.1.2 Variable load systems 3.2 Controller Options • . 3.2.1 Phase angle control 3.2.2 Binary weighted loads ~ 3.2.3 Mark- Space ratio controller 3.3 Comparison over synchronous generator 3.3.1 Options of voltage frequency variables. 3.3.2 Advantage of the induction motor an generator 3.3.3 Disadvantages of the induction motor an generator. CHAPTER 4 METHODOLOGY 4.1 4.2 4.3 Methodology Tests carried out Analyzing the system using software IV II 12 15 16 19 20 20 23 24 27 27 28 30 30 31 32 35 35 36 37 38 45 45 CHAPTER 5 OBSERVATION /RESULTS / OAT/\ 5.1 Determination of excitation capacitance in conventional way 46 5.1.1 Electrical test Method 46 5.1.2 Induction motor performance data. 47 5.1.3 Excitation capacitance for Induction Generator when the maximum output at minimum unbalance. 47 5.2 Determination of correct capacitor connection (Power output test) 47 5.3 Winding current test ;I 49 5.4 Generator performances 49 5.4.1 Performances at calculated capacitance value 49 5.5 Performances of the generator with di ffcrent excitations 51 5.6 Generator performances at minimum unbalance and maximum power output at optimum excitation 53 5.6.1 Current variation in the system. 54 5.6.2 Voltage variation in the system 55 .... 5.6.3 Harmonics in the system 56 5.7 Generator performances with continuous operation 57 5.7.1 Thermal response 58 5.7.2 Power variation in the system 58 5.7.3 Temperature and frequency variation 59 5.8 Generator system parameters at maximum power at minimum unbalance with different excitation 59 5.8.1 Voltage variation in the system 60 5.8.2 Load variation in the system 61 5.8.3 Current variation in the system 61 5.9 generator performance -with induction generator controller 62 5.9. I Generator performance when resistive load in the system 62 5.9.1.1 Harmonics variation in the system 63 v 5.9.1.2 Output voltage variation in the system 63 5.9.2 Generator performance with IGC for reactive power loads 64 5.9.2.1 5.9.2.2 Speed variation in the system Power Factor variation in the system 5.10 Other analysis of the system 5.1 0.1 Finding parameters using flow charts 5.10.2 Finding generator parameters using sofuvare CHAPTER6 SYSTEM ANAL YSISING/ DISCUSSION CII \PIER 7 CONCLUSION REFERENCES ABBRIVJA TIONS APPENDIX Appendix I Generator system data Appendix 2 Visual Basic programme code ·- .-1 VI I 64 65 72 75 81 84 88 90 92 93 99 CHAPTER 1 1.1 1.2 1.3 1.4 1.5 LIST Of TABLES Distribution of all sites by the status of sites and capacity Completed Pico scale hydro projects in Sri Lanka by status of districts Generating capacities of completed projects Pico scale hydro projects in Sri Lanka projects in progress Generating capacities projects in progress CHAPTERS 5.1 5.2 5.3 5.7 5.8 Determination of correct capacitor connection in the system Generator performance at conventionally calculated cap{citance value Induction generator performances at different excitation Generator performances at minimum unbalance and maximum power output at optimum excitation 5.9 Generator performances in continuous operation. 5.10 Characteristics of the generator at Balance Operation with different excitation 5.11 Induction generator parameters with IGC f.or Resistive Loads 5.12 Induction generator parameters ~ith IGC for Reactive Loads ~ 5.13 Recommended motor voltage ratings 5.14 K values CHAPTER 6 6.1 APPENDIX A-1 A-2 A-3 Details from the presently running generators Motor performance data Current - carrying capacity Voltage Drop VII 1.1 1.2 1.3 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 LIST OF FIGURES CHAPTER 1 Completed Pico scale hydro projects in Sri Lanka Pico scale hydro projects in Sri Lanka in progress Cumulative gr0\\1h in Pico scale hyd ro projects in Sri Lanka CHAPTER2 Power flow of a three phase induction motor Power flow of an induction machine in generator operatiolj Typical magnetization curve of a common core material and Increase of reactive current in generator operation Self excitation of an induction machine by a capacitor in parallel at no load Development of voltage at increasing load and demagnetization limit- loading at constant frequency Development of voltage at increasing load and demagnetization limit- .... loading at deceasing frequency Typical torque speed characteriStics of a squirrel cage induction machine The circle diagram Frequency variation of an IGC controlled induction generator when loaded with an induction load 2.10 Single -Phase output from a three phase machine 2.11 C-2C connection for a three- phase Induction Generator with a single phase resistive load 2.12 Voltage and current phasor diagrams for a cos