This article discusses formulas for the surge/characteristic impedance of vertical conductors. Calculated results of the surge impedance are compared with measured results on vertical conductors and transmission towers. The accuracy of the available time-domain formulas is not satisfactory except for Hara's formulas, while the frequency-domain formulas show satisfactory accuracy. A two-stair model representing a nonuniform transmission tower is investigated based on ABCD parameters, and an approximate characteristic impedance of the nonuniform tower is derived. The circuit-theory approach and finite-difference time-domain (FDTD) computed results using the two-stair model are shown to give better agreement with measured results on UHV and 500-kV towers than those obtained using a single-conductor approximation (uniform line). The FDTD computed results clearly show the position-dependence of line parameters. Existing time-domain formulas describe only the surge impedance seen from the tower top or from the tower base, and thus, are not applicable to a lightning shielding failure studies involving back-flashover, which require the knowledge of the surge impedances of the upper, middle, and lower parts of the tower.

中文翻译：

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输电塔多级模型的阻抗和导纳公式

本文讨论了垂直导体的浪涌/特性阻抗的公式。将浪涌阻抗的计算结果与垂直导体和输电塔的测量结果进行比较。除了 Hara 的公式，可用的时域公式的精度并不令人满意，而频域公式的精度令人满意。基于ABCD参数研究了代表非均匀输电塔的两级模型，并推导出了非均匀塔的近似特征阻抗。电路理论方法和使用两级模型的有限差分时域 (FDTD) 计算结果与使用单导体近似（均匀分布）获得的结果相比，与 UHV 和 500 kV 塔的测量结果更加吻合。线）。FDTD 计算结果清楚地显示了线参数的位置相关性。现有的时域公式仅描述从塔顶或塔底看到的浪涌阻抗，因此不适用于涉及回闪的雷电屏蔽故障研究，这需要了解上部浪涌阻抗，塔的中部和下部。