| Summary: | 碩士 === 逢甲大學 === 電機工程所 === 91 === The direct current (DC) offset component of current will be produced when the fault occurs in power system. If this DC offset of current is flowing into a protective current transformer (CT), it will cause the core of CT to saturate and produce a distorted secondary current because of too large DC offset component, and core hysteresis results in a residual flux that also affects the CT transient behavior. Using Jiles-Atherton (J-A) model, in convention, need the known excitation current of ferromagnetic core or magnetic field, and just can build ferromagnetic hysteresis curve. However, it is more difficult to measure CT excitation current or magnetic field, when CT saturates. Hence, the anticipation of saturation characteristic of ferromagnetic core or hysteresis curve of CT is more difficult. In this study, for overcoming above shortcoming, we propose to use both inverse model of J-A theorem and terminal voltage of relay to simulate, when the power system faults, transient behavior (transient exciting current of ferromagnetic core) of CT cores. On the other hand, the aspect of reactance and transformer, it is seriously transient over voltage occurs, which is induced by the phenomenon of current chopping. Accordingly, in this study we simulate and analyze current chopping in the equipment of reactance and discuss the influence of current chopping to core magnetic circuit of reactance. As a result, the model of core magnetic circuit, in conventionality, merely analyzes the inner property of ferromagnetic core but could not combine outer circuit to analyze the transient analysis of the hysteresis situation of ferromagnetic core when the fault occurs. Consequently, we apply the inverse J-A model to compute, which use the first order non-linear differential equation and make the complete circuit simulation for the behavior of ferromagnetic core and outer circuit.
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