Lightning attachment models and perfect shielding angle of transmission lines

General relationships for the estimation of the perfect shielding angle of overhead transmission lines have been derived by performing shielding analysis on the basis of several lightning attachment models, including a recently introduced statistical one. The interdependence of perfect shielding angle, transmission line height and minimum current causing flashover of insulation is demonstrated as influenced by the lightning attachment model employed in shielding analysis. There is a great variability in perfect shielding angle among lightning attachment models; this is demonstrated for 150 kV and 400 kV lines of the Hellenic transmission system. The applicability of lightning attachment models in perfect shielding angle calculations is evaluated based on the shielding performance of transmission lines; the IEEE Std 1243:1997 yields consistent results with respect to the shielding performance of the lines.