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School of Electrical, Computer and Energy Engineering M.S. Final Oral Defense Influence of Grounded Back Electrode on AC Creepage Breakdown Characteristics by Jiajun Liu April 11, 2014 3 pm ERC 490 Committee: Dr. George Karady (chair) Dr. Raja Ayyanar Dr. Keith Holbert Abstract This thesis focuses on the influence of grounded back electrode on the breakdown characteristics. With growing high voltage transmission grid, the reliability of the high voltage devices attracts more attention than before. Insulation with grounded back electrode is a common type of insulation which is adopted in many high voltage power devices. While most of the power equipment work under AC voltage, most of the research on back electrode is focused on the DC voltage. Therefore, it is necessary to deeply investigate the influence of back electrode under AC applied voltage. To investigate the influence of back electrode, the research is separated into two phases, which are the experiment phase and the electric field analysis phase. In the experiments, the breakdown voltages for both with and without back electrode are obtained. The experimental results indicate that the grounded back electrode does have impact on the breakdown characteristics. Then with the breakdown voltage, based on real experiment model, the electric field is analyzed using computer software. From the field simulation result, it is found that the back electrode also influences the electric field distribution. The internal relationship between the electric field and breakdown voltage is the key to explain all the results and phenomena observed during the experiment. Additionally, the influence of insulation barrier on breakdown is also investigated. Compared to the case without ground electrode, inserting barrier into the gap can more significantly improve breakdown voltage.