G i&lbortl&lw EMBEDDED GENERATION IMPACTS TO MEDIUM VOLTAGE DISTRIBUTION NETWORK 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 Science by B. A. P. THILAK KUMARA PERERA LIBRARY UNIVERSITY OF MORATUWA, SRI LANKA MORATUWA Supervised by: Dr. J. P. Karunadasa Department of Electrical Engineering University of Moratuwa, Sri Lanka University of Moratuwa 92968 January 2009 o 3 2 9 0 3 T ^ DECLARATION The work submitted in this dissertation is the result of my own investigation, except where otherwise stated. It has not already been accepted for any degree, and is also not being concurrently submitted for any other degree. | B. A. P. T. K. Perera Date : 30/01/2009 I endorse the declaration by the candidate. Dr. J. P. Karunadasa CONTENTS Declaration j Abstract i v Acknowledgement v List of Abbreviations v i List of Figures vi'1 List of Tables x 1 Introduction 1.1 Background 1 1.2 Motivation 3 1.3 Objective 4 1.4 Scope of work 4 2 MV distribution system of Sabaragamuwa province of Sri lanka 2.1 Sabaragamuwa Province 5 2.2 Electricity Distribution Network of Sabaragamuwa Province 5 2.3 Rathnapura Grid Substation 6 2.4 Updating the map of MV distribution network 9 2.5 Data Collection 9 2.6 Modeling the network using SynerGEE 9 2.7 Assigning input data to the digitizing model 10 2.8 Modeling the network using MATLAB 11 2.9 MHP Data 16 3 Analysis and Results 3.1 Voltage Regulation IB 3.2 Fault Level Analysis 20 3.3 Obtaining maximum fault currents 22 4 Proposed Solutions 4.1 Voltage Regulation 25 4.2 Increasing the Fault Level 25 ii 4.3 Fault Current Limiters 4.4 Application of Fault Current Limiters 29 4.5 Thyristor Control Series Capacitor as FCL 32 4.6 Introduction to TCSC 33 4.7 Proposed TCSC for distribution network applications 35 4.8 Selection of operation regions 37 4.8 Testing and simulation of prototype TCSC 41 5 Conclusions 5.1 Conclusions 43 5.2 Suggestions for future works 44 References 45 Appendix A : Grid vice connected MHP s in Sri Lanka 47 Appendix B : Conductor Data 48 Appendix C : SynerGEE Table and Maps 49 Appendix D : Calculating the source impedance 53 Appendix E : Circuit Diagrams and Graphs 54 Appendix F : Types of fault Current Limiters 60 iii Abstract As a result of increasing of electricity demand, the electrical transmission and distribution systems are continuously expanding. Connection of Distribution Generators (DG) to the distribution network and upgrading of the transmission lines are more frequent expansions. Connection of new mini hydro power plants (MHPs) in Sri Lanka is one good example. In most of the cases these DGs, which are mainly based renewable energy are located in remote areas. The main bottleneck barrier of connecting DG is violation of fault current ratings at some parts of the network. Some expansions may result in higher fault current level at some points of the power system and thus exceeding the short circuit ratings of equipment such as switchgears and expulsion switches. As upgrading of equipment is not feasible both economically and technically, introduction of fault current limiting devices has become an essential requirement. Fault Current Limiter (FCL) is series device connected to the power system, which shows the high impedance to the current during a fault while showing a zero or low impedance during normal loading condition. Although several FCL topologies were introduced by researchers, there are some technical and economical problems to be solved before introducing them to the power system effectively. It demands the investigation of new FCL topologies which are more feasible or modifications of available topologies to increase feasibility. FCL introduces additional impedance to the system depending on the system operating conditions. It is not only reduces the fault current but also effects on a number of power system related phenomena such as power losses, protection coordination, interrupting duty of switchgears, transient stability and voltage sag. This research work is mainly focus on application of Fault Current Limiter (FCL) to overcome this problem and facilitate the equipment safety. iv Acknowledgement First I thank very much Dr. J. P. Karunadasa without whose guidance, support and encouragement, beyond his role of project supervisor this achievement would not be end with this final dissertation successfully. I also thank Mrs. Chulani Gamlath - System Planning Engineer (Sabaragamuwa Province), Mr. R. Ekanayake the distribution planning branch, Mrs. B. G. Geethani - System Planning Engineer (WPS II) for facilitating me necessary data and the information. I would also like to express my appreciation to all my colleagues in Post Graduate programme and particularly to Amala, Palitha, Hetti, Weli and Jayasooriya for their encouragement. Last but not least my gratitude goes to my dear parents, wife and family members for their love, moral support and understanding from start to end of this course. v List of Abbreviations AAAC All Aluminium Alloy Conductor ABS Air Break Switch ACSR Aluminium Conductor Steel Reinforced CB Circuit Breaker CEB Ceylon Electricity Board CSC Consumer Service Centre DDLO Drop Down Lift Off DG Distributed Generator FCL Fault Current Limiter GSS Grid Substation GTO Gate Turn Off HTS High Temperature Superconducting I Current Ic Critical current Jc Critical Current density LBS Load Break Switch LT Low Tension LV Low Voltage MFCL Magnetic Fault Current Limiter MHP Mini Hydro Power . MOV Metal MV Medium Voltage PSS Primary Substation RGSS Rathnapura Grid Substation SC Superconductor SFCL Superconducting Fault Current Limiter SIN System Identification Number SPP Small Power Producers SPPA Small Power Purchase Agreement StFCL Static Fault Current Limiter Tc Critical Temperature TCSC Thyristor Control Series Capacitor TCR Thyristor Controlled Reactor vii List of Figures Figure Page Figure 2.1 Single Line Diagram of Rathnapura Grid Substation 07 Figure 2.2 Single line Diagram of Feeder No: 05 12 Figure 2.3 Single line Diagram of Feeder No: 06 14 Figure 2.4 Single line Diagram of Feeder No: 08 15 Figure 4.1 FCL at primary distribution feeder 30 Figure 4.2 FCL at distribution transformer circuit 31 Figure 4.3 FCL at connection point of DG 32 Figure 4.4 Basic structure of TCSC 33 Figure 4.5 Impedance characteristic of TCSC 34 Figure 4.6 Configuration of TCSC and control system 36 Figure 4.7 Expected firing angle variation of line current 37 Figure 4.8 Wave forms of the firing pulses 39 Figure 4.9 Circuit Diagram of TCSC 40 Figure C.l Feeder 05 50 Figure C.2 Feeder 06 51 Figure C.3 Feeder 08 52 Figure E. l Modeled Feeders of RGSS without DG s 54 Figure E.2 Modeled Feeders of RGSS with DG s 55 Figure E.3 Application of designed FCL to the network 56 Figure E.4 Fault Current at the point of J, without DG s 57 Figure E.5 Fault Current at the point of J, with DG s 57 Figure E.6 Fault Current at the point of J, with FCL 57 Figure E.7 Fault Current at the point of H, without DG s 58 Figure E.8 Fault Current at the point of H, with DG s 58 Figure E.9 Fault Current at the point of H, with FCL 58 Figure E.10 Fault Current at the point of S, without DG s 59 Figure E.l 1 Fault Current at the point of S, with DG s 59 Figure E . l 2 Fault Current at the point of S, with FCL 59 viii Figure Page Figure F.l Layout of Resistive type SFCL 61 Figure F.2 Layout of Magnetic Shielding type SFCL 62 Figure F.3 Layout of Saturated Inductive type SFCL 63 Figure F.4 Equivalent circuit of Flux Lock type SFCL 64 Figure F.5 Equivalent circuit of Magnetic switch based MFCL 65 Figure F.6 Passive MFCL with series biasing 66 Figure F.7 Passive MFCL with parallel biasing 67 Figure F.8 GTO thyristor switch based 68 Figure F.9 Thyristor controlled series tune circuit based StFCL 69 Figure F.10 Impedance characteristics of TCSC 69 ix List of Tables Table Page Table 2.1 MV distribution facilities of Rathnapura Grid Substation 07 Table 2.2 MV Feeder Data 08 Table 2.3 Data of connected MHP s 08 Table 2.4 Conductor Data of Feeder No: 05 13 Table 2.5 Conductor Data of Feeder No: 06 14 Table 2.6 Conductor Data of Feeder No: 08 16 Table 2.7 MHP Generator Data 01 16 Table 2.8 MHP Generator Data 02 17 Table 2.9 MHP Generator Data 03 17 Table 2.10 MHP Generator Data 04 17 Table 3.1 Voltage variation of feeder sections 20 Table 3.2 Comparing fault currents and without DG s 23 Table 4.1 Performance Data for FCL 42 Table A.l Grid vice connected MHP s in Sri lanka 47 Table B.l Resistances and reactances of conductor types 48 Table C.l SynerGEE Table and Maps 49 x