A systematic approach to the evaluation of the influence of multilayered Earth on overhead power transmission lines

The influence of earth stratification on overhead power transmission line impedances is investigated in this paper. A systematic comparison of existing approaches is done, while results are also obtained using a finite-element method formulation. A novel numerical integration technique is proposed for the calculation of the infinite integrals involved. Typical single- and double-circuit line configurations are examined for a combination of layer depths and earth resistivities over a wide frequency range. The influence of the layer depth is also investigated. Results show significant differences from those, corresponding to the case of homogeneous earth. Using the multilayered earth return impedances in transient simulations, the transient responses show that differences occur mainly in cases of asymmetrical faults, justifying the need for a detailed earth model implementation.

I. Introduction

In transient simulations, detailed transmission line modeling is required. Transmission line modeling is strongly influenced by the presence of the resistive earth return path, which is included in transmission line impedances through proper correction terms. The latter are calculated using the widely accepted Carson's formulas [1] developed for the case of semi-infinite, homogeneous earth.