Lightning protection of transmission lines: optimal shielding design procedure

The paper first derives a set of shielding constraints which must be satisfied for achieving effective shielding against lightning for all of the phase conductors of an overhead transmission line in relation to earth-wire placement. The shielding constraints are obtained from the analysis related to the rigorous proof of the premise that, once the earth-wire position has been determined to achieve effective shielding for a nominated critical lightning stroke current, then shielding of the phase conductors is still maintained for stroke currents greater than the critical value. An optimal shielding design procedure is then developed in which the cost function relating to earth-wire position(s) is minimised subject to shielding constraints and specified clearance constraints. Results of lightning protection designs using the procedure, to achieve effective shielding for a range of transmission-line configurations, are presented.