| Accurate modeling of frequency dependence of transmission line is of essential importance for the correct simulation of electromagnetic transient conditions. A model for frequency dependent transmission lines has been acquired in this paper via fitting impedance by vector fitting combined Analogy of the Multi-conductor Transmission Lines (MTLs) Equations to the State-Variable Equations. At the same time, the results in time domain has been calculated by the NILT (Numerical Inversion of Laplace Transforms). The equivalent model programmed by MATLAB in the paper has been applied to practical circuits and the results has been validated by comparing the results from EMTP software. Combined with projects of Hebei Electric Power Research Institute, the power frequency overvoltage, switching overvoltage, arc current, restoring overvoltage of two 500kV transmission lines has been caculated and proposed that the High Voltage Circuit Breaker Closing Resistance could be cancelled.
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