On the use of the finite conductor length approach for the calculation of electromagnetic transients in overhead transmission lines

Despite the progress that has been made in the representation of the imperfect earth, the majority of the most-known earth formulations assume that the Overhead Transmission Line (OHTL) is infinitely long. In this paper, earth-return correction terms for finite length OHTL are presented and compared to formulas of infinite line length. For this purpose, the corresponding per-unit-length parameters and propagation characteristics of a high-voltage OHTL of variable line length are compared. An empirical limit is also proposed, under which the finite conductor length approach should be taken into consideration. The analysis proceeds with the evaluation of the performance of the OHTL under steady-state and transient phenomena with divergences being observed for small line lengths, confirming the proposed length limit. The investigation reveals that the results from the finite conductor length approach can be on the safe side, therefore this approach should be taken into account.