報告書番号

T02049

タイトル（和文）

回転対称な垂直接地電極に関するインピーダンスの解析手法

タイトル（英文）

Development of computational method of impedance with respect to vertical and rotatory-symmetric grounding electrodes

概要 （図表や脚注は「報告書全文」に掲載しております）

電力設備接地系の接地抵抗特性は耐雷設計上の重要な要因であるため，その簡便な推定ができ，これを電力系統の汎用過渡現象解析ソフトEMTPに組み込むことができれば実用的な意味は大きい。EMTPは，避雷器，地面に平行な線路などの解析には威力を発揮してきた。これは，EMTPでは波長に比べて解析対象物の寸法が無視できる場合や平面波が伝搬すると仮定してよい状態を解析対象とし，それらを集中定数や分布定数線路によりモデル化できたことによる。しかし地面に垂直な接地電極などの垂直導体系では，先の場合とは電磁波の伝搬形態が異なる状況において，無限遠点に対する特性や平面波近似ができない早い時間領域での特性が要求されるため，そのモデル化が困難であった。 本報告では，配電用接地棒に代表される地表面に垂直で回転対称な接地電極について，地表面から見たインピーダンス（軸方向インピーダンス）を定義し,それをFDTD過渡応答特性解析手法から求め，さらにRLC等価回路を同定する手法について述べている。

概要 （英文）

It is important to study the transient performance of grounding systems for lightning surges, in order to ensure the electromagnetic compatibility (EMC) of sensitive electronics such as information devices and digital relays in substations and/or residential houses. Therefore, an easy method of estimating frequency response in order to represent the transient performance of grounding systems and its incorporation into EMTP are highly desired. EMTP based on circuit theory has been applied to resolve the transient performance of electrical apparatus consisting of cables and conductors parallel to the ground surface, which implicates propagation of TEM waves that are plane waves, and devices such as surge arresters represented by lumped elements. However, conductors vertical to the ground surface have not been modeled because TM waves propagate on such conductors and the characteristics in early time, when the approximation of plane waves is not adapted, are required. In this paper, we proposed axial impedance of the vertical and rotatory-symmetric grounding electrode, which was the complex ratio of the potential of its top at the ground surface to the current flowing into it in frequency-domain. The potential in time-domain was derived from the integral of the horizontal component of electric fields on the ground surface, and could be defined uniquely in the configuration discussed here. We then calculated the potential and current in time-domain from the method for computational analysis of transient performance based on the FD-TD method and the axial impedance in frequency-domain was derived using the Fourier transforms of the potential and current in time-domain. Finally, we applied the identification method to obtain the equivalent circuit consisting of lumped elements from the frequency response of the axial impedance.

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