| Summary: | 碩士 === 國立臺北科技大學 === 電機工程系研究所 === 95 === In this thesis, the characteristics of line ground faults occurred nearby the typical outdoor open type of extra-high voltage substation (E/S) are analyzed, and their affections on the substation breaker control system are investigated. The circuit model considering the main transformer, primary and secondary buses and transmission lines, and the downstream substation loads are constructed by using electromagnetic transient program/alternative transient program (EMTP/ATP). Based on the circuit model, the bus voltages, transformer output currents and neutral currents, and transmission currents, are analyzed with respect to various fault ground impedance, and different load levels of downstream substations. The currents injected into grounding system will be found from neutral bus currents of main transformers. Then, the grounding system characteristics due to line ground fault can be analyzed by using a software package for grounding analysis called CDEGS. By which, the distributions of ground potential rise (GPR), ground surface magnetic field, and grid conductor current can be analyzed. Finally, based on these analysis results and the measured data from a practical case of E/S to be surveyed, the affections of grounding system on the breaker control system are evaluated. The study results had shown that the GPR and magnetic field of grounding system will produce detrimental effects on the breaker control system. Especially, for those poor insulation control lines, large GPR and longitudinal induction voltage during ground fault may lead to flash-over at control line terminals and thus inducing breaker mis-trip out. For the practical case in this thesis, to do well maintenance and to renew those old breakers and control lines with poor insulation situations are very important strategy for preventing breaker mis-tripping. Other protection measures from GPR and magnetic field induction interferences are important too. This study may provide useful information for planning the protection measures.
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