On Inductance of Buried Horizontal Bare Conductors

External inductance is one of the basic quantities in the classical approach to the surge and high-frequency analysis of buried horizontal bare conductors. However, there is no consensus, in the modern literature, on the treatment of the effects of the earth surface in the approximate expressions for the inductance, and several different formulas are often used. In this paper, we derive a new expression for the external inductance of buried horizontal conductors that accurately takes into account the effects of the earth surface and compare the errors of the usual approximate formulas. We also propose new approximate formulas that lead to smaller errors for depths of burial less than or equal to 1 m.