Earth line

Japanese: 地線 - ちせん

A grounded metal wire used mainly for lightning protection of power transmission lines. There are overhead ground wires that are stretched over the top of a power transmission conductor to protect the conductor from direct lightning strikes, and buried ground wires that are buried in the legs of a pylon to safely channel the lightning current that strikes the overhead ground wire to the ground. A buried ground wire that connects two adjacent pylon legs is called a continuous ground wire. Even if an overhead ground wire prevents a direct strike on the conductor, if the lightning current is large, the potential of the pylon may rise and cause a reverse flashover (flashover). Overhead ground wires are usually used with one to three strips, but a larger number of strips not only increases the area that is protected from direct lightning strikes, but also has the effect of suppressing the rise in the potential of the pylon.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

接地をした金属線でおもに送電線の雷防護に用いられる。送電用導体の上部に張って導体を雷の直撃から守る架空地線と，架空地線に落ちた雷の電流を安全に大地へ流すため鉄塔の脚部に埋める埋設地線がある。埋設地線で隣接する二つの鉄塔脚を結んだものを連設地線という。架空地線によって導体直撃が防止されても，雷撃電流が大きい場合には鉄塔の電位が上昇して逆フラッシオーバー(フラッシオーバー)が生ずる可能性もある。架空地線は通常1～3条が用いられるが，条数が多いと直撃雷を防ぐ範囲が広がるほかに鉄塔電位上昇を押さえる効果もある。

出典　株式会社平凡社世界大百科事典第２版について　情報

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