Determination of optimal shielding angles in shielded transmission line design

The paper develops a general formulation that gives expressions for the exposure distance of transmission line conductors to direct lightning strikes in terms of striking distances, conductor heights, cross-arm lengths and shielding angles. The expressions are applicable to different electrogeometric models (EGM). They provide the basis on which optimal shielding angle is determined in the design of earthwires. Constrained minimisation of the exposure distance gives the optimal value for shielding angle. The expressions are validated using the published field results. Using the general expressions developed, investigations are carried out to identify the factors on which optimal shielding angle depends and to quantify the degree of dependencies. Sensitivity of the optimal shielding angle to different EGMs is evaluated in the paper