抄録
This paper explains an error involved in well-known formulas of the earth-return impedance of an overhead multi-conductor derived by Pollaczek, Carson and Sunde. It has been said that Pollaczek's infinite integral formula is numerically instable, and Carson's formula cannot deal with displacement currents. This paper has shown an accurate earth-return impedance formula considering the displacement currents, and Carson's formula is modified so as to be able to deal with the displacement currents. Also, an approximate formula considering the displacement currents is derived. The formula is of a simple closed form and is applicable to high frequencies.
