| Summary: | 碩士 === 國立清華大學 === 電機工程學系 === 91 === Taiwan’s Synchronous Radiation Research Center （SRRC） located at Hsinchu has been suffered with the multitripps of accelerator and with the instability of electron beam. Two possible reasons for the multitripping and beam instability are: the voltage fluctuation of power supply and the high frequency stray current leaked into the ground mesh or ground electrodes. The latter could interfere the control devices for the accelerator. Because both reasons have connection with ground electrodes, SRRC established a new one which grounding resistance was designed to be lower than 0.2Ω in 2002. Meanwhile SRRC investigated the original ground electrodes which are under the accelerator to look for improvements. However the research was deficient in simulations for ground electrodes, many judgments and suggestions was lack of the identification of theories.
To simulate Grounding Potential Difference (GPD), local researchers applied the Electro Magnetic Transient Program (EMTP) more frequently than the Current Distribution Electromagnetic Grounding and Soil Structure Analysis (CDEGS), the latter being a software designed specially for simulating GPD. In the mesh model of EMTP, the conductors of ground mesh are simulated as RL circuits, which neglects the interaction among conductors and the modeling requires precise estimation of parameters. Both can thus result in simulation error. As such, there is a necessity for applying of the softwares with special design for GPD simulation, such as CDEGS, which could be the future mainstream of GPD simulation.
Taiwan is presently lacking researches on the methods of GPD simulation, in particular for those specially designed softwares. What are their assumptions? Have their individual subroutines been tested for accuracy validation? Where are their sources for the simulation errors? All these demand in-depth research. More clearly, Taiwan needs a comprehensive literature on the computation methods for GPD simulation, as an important reference for the future GPD simulation and the overvoltage event diagnosis.
Consequently, the thesis firstly focuses on the potential fluctuation causing by the fault or inrush current which is injected into ground electrodes. Secondary it studies the potential fluctuation causing by the high-frequency current which is leaking into the ground. The former belongs to the grounding safety problems, and the latter belongs to the EMI topics. The thesis is divided into three folds, part 1 shall study the grounding simulation method of CDEGS. Part 2 shall compare different ground electrodes via simulation, including: the magnitude of ground electrode or injecting current, soil resistance coefficient, the depth of ground electrode and the position of injecting current etc.. This part also discusses a flat long row which is made up by cylinder conductors. Part 3 shall simulate the new ground electrodes of SRRC, and simulate the GPD between old and new ground electrodes while the kicker with high frequency of 830 kHz and large current of 6.5 kA is operating. The former simulates the low frequency, and the latter simulates the high frequency. Both are compared with the measurement results and the validities of the simulations are also discussed.
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