| In recent years, with the development of the power grid construction and the emergency of high pressure gas-insulated substation (GIS), very fast transient overvoltage (VFTO) getting more attentions because of the high-frequency oscillation voltage caused more harm in power grid than ever.Traditional equivalent circuit model with simple structure and clear physical meaning has been used widely. At low-frequency condition, the traditional equivalent circuit can achieve an accurate simulation of devices. However, with the growing demand of broadband modeling, the defect of traditional equivalent circuit model becomes significant, after analyzed a variety of existing broadband modeling methods, this paper present a new way of modeling by combining the traditional equivalent circuit model with black-box modeling method.As the Passivity of the system has very important significance, the model will be ineffective if the passivity of the system can’t be guaranteed. Therefore, after admittance functions been obtained by the vector fitting method, the global passivity enforcement method and the network Synthesis were introduced.In addition, under conditions, such as hysteresis, eddy current and saturation phenomena, the magnetization curve of the transformer core will be strong non-linear, it becomes particularly evident while in the large-signal conditions. Based on the core components of nonlinear characteristics, this paper established the nonlinear model by a nonlinear resistor and a nonlinear inductance connected in parallel at the excitation branch. In the process of building the broadband model, linear parts been used instead of nonlinear model at the small-signal conditions. After combined the broadband model with the non-linear excitation branch, the establishment of non-linear broadband voltage potential transformer model achieved.At last, compared the simulation with experimental data, and the correctness and feasibility of this method been verified. |
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