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Performance Analysis of Composite Insulators up to 1200 Kv Ac Using

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Performance Analysis of Composite Insulators up to 1200 Kv Ac Using Performance Analysis of Composite Insulators up to 1200 kV ac using Electric Field Calculations by Tanushri Doshi A Thesis Presented in Partial Fulfillment of the requirements for the Degree Master of Science Approved November 2010 by the Graduate Supervisory Committee: Ravi Gorur, Chair Richard Farmer Vijay Vittal ARIZONA STATE UNIVERSITY December 2010 ABSTRACT This research work illustrates the use of software packages based on the concept of nu- merical analysis technique to evaluate the electric field and voltage distribution along composite insulators for system voltages ranging from 138 kV up to 1200 kV ac. A part of the calculations was made using the 3D software package, COULOMB 8.0, based on the concept of Boundary Element Method (BEM). The electric field was calculated under dry and wet conditions. Compos- ite insulators experience more electrical stress when compared to porcelain and are also more prone to damage caused by corona activity. The work presented here investigates the effect of corona rings of specific dimensions and bundled conductors on the electric field along composite insulators. Inappropriate placement or dimensions of corona rings could enhance the electric field instead of mitigating it. Corona ring optimization for a 1000 kV composite insulator was per- formed by changing parameters of the ring, such as the diameter of the ring, thickness of the ring tube and the projection of the ring from the high voltage energized end fitting. Grading rings were designed for Ultra High Voltage (UHV) systems that use two units of composite insulators in par- allel. The insulation distance, which bears 50% of the total applied voltage, is raised by 61% with the grading ring installed, when compared to the distance without the grading ring. In other words, the electric field and voltage distribution was found to be more linear with the application of grad- ing rings. The second part of this project was carried out using the EPRI designed software EPIC. This is based on the concept of Charge Simulation method (CSM). Comparisons were made be- tween electric field magnitude along composite insulators used for suspension and dead end con- figuration for system voltages ranging from 138 kV to 500 kV. It was found that the dead end composite insulators experience significantly higher electrical stress when compared to their sus- pension counterpart. It was also concluded that this difference gets more prominent as the system voltage increases. A comparison made between electric field distribution along composite insula- tors used in single and double dead end structures suggested that the electric stress experienced by the single dead end composite insulators is relatively higher when compared to double dead end composite insulators. ii To my parents Seema Doshi and. Tarun Doshi and brother Rishabh, whose support is ever so precious iii ACKNOWLEDGMENTS I would like to sincerely thank my mentor and chair Dr. Ravi S. Gorur for his advice and continued support throughout my course. I greatly acknowledge and thank Mr. Jim Hunt from Salt River Project for providing me with an opportunity to work on this project. I express my gratitude towards Professor Farmer and Dr. Vijay Vittal for their time and consideration in being on my supervisory committee. I am also obliged to the faculty of the power systems group at Arizona State University for their guidance throughout my tenure here. I would like to thank my parents and brother for their extended support without which this would not have been possible. I would also like to extend a special thanks to all my friends from Visvesvaraya National Institute of Technology and Arizona State University for always standing by me. iv TABLE OF CONTENTS Page TABLE OF CONTENTS ................................................................................................................v LIST OF TABLES ......................................................................................................................... ix LIST OF FIGURES .........................................................................................................................x NOMENCLATURE ..................................................................................................................... xiii CHAPTER 1. INTRODUCTION .......................................................................................................................1 1.1 Introduction to Outdoor Insulation ................................................................................1 1.2 Research Objectives ......................................................................................................3 1.3 Organization of this Thesis ...........................................................................................4 2. LITERATURE REVIEW ............................................................................................................5 2.1 Introduction ...................................................................................................................5 2.2 Types of Insulators ........................................................................................................5 2.2.1 Porcelain Insulators......................................................................................5 2.2.2 Glass Insulators ............................................................................................6 2.2.3 Non-ceramic Insulators ................................................................................7 2.3 Causes of Failure ...........................................................................................................8 2.3.1 Handling ......................................................................................................8 2.3.2 Vandalism ....................................................................................................8 2.3.3 Manufacturing Defects ................................................................................9 2.3.4 Flashover......................................................................................................9 2.3.5 Corona Degradation ................................................................................... 11 2.3.6 Voltage Stress ............................................................................................ 12 3. ELECTRIC FIELD ANALYSIS TECHNIQUES ...................................................................... 13 3.1 Introduction ................................................................................................................. 13 3.2 Experimental Field Analysis Technique ..................................................................... 13 3.2.1 Impedance Networks ................................................................................. 14 v CHAPTER Page 3.2.2 Electrolytic Tank........................................................................................ 14 3.3 Analytical Field Analysis Techniques ......................................................................... 14 3.4 Numerical Field Analysis Techniques ........................................................................ 14 3.4.1 Finite Difference Method ........................................................................... 17 3.4.2 Finite Element Method .............................................................................. 17 3.4.3 Charge Simulation Method ........................................................................ 18 3.4.4 Boundary Element Analysis ...................................................................... 20 4. ELECTRIC FIELD ANALYSIS OF COMPOSITE INSULATORS ........................................ 23 4.1 Introduction ................................................................................................................. 23 4.2 Composite Insulators Dimensions ............................................................................... 23 4.3 Base Case – Electric Field Analysis under Dry Conditions ........................................ 26 4.3.1 Modeling Insulator Geometry .................................................................... 26 4.3.2 Assigning Material Properties .................................................................... 27 4.3.3. Assigning Boundary Conditions ............................................................... 27 4.3.4 Assigning Boundary Elements ................................................................... 28 4.3.5 Assumptions and Simplifications .............................................................. 29 4.3.6 Results for Dry Case .................................................................................. 30 4.3.7 Error Checks .............................................................................................. 32 4.4 Electric Field Analysis under Wet Conditions ............................................................ 32 4.4.1 Insulator Geometry .................................................................................... 33 4.4.2 Assigning Physical Conditions .................................................................. 34 4.4.3 Assigning Boundary Elements ................................................................... 34 4.4.4 Electric Field Analysis for Wet Case ......................................................... 34 4.5 Effect of Addition of Corona Rings under Dry Conditions......................................... 36 4.6 Effect of Bundled Conductors on Electric Field along Composite Insulators ............
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