Modeling of Substation Shielding Against Direct Lightning Strikes

The paper comprises the first application of the concept of upward leader inception and propagation to meet the downward negative leader in a final jump, to assess shielding of substations against direct lightning strikes. Expressions for the attractive radius of a slender mast and the lateral attractive distance of a shield wire are used to determine the respective protection zones. The analysis is extended to account for lightning protection provided by double masts as well as by four masts placed at the corners of a rectangular area. Lightning protection by double ground wires is also analyzed. The model takes into account not only the different lightning protection characteristics of masts and ground wires, but also distinguishes between rod-type and conductor-type protected objects. The model considers not only flashes descending on the substation from above, but also accounts for shielding against side flashes. A systematic approach is presented in sufficient detail to allow practical application to shielding design of substations. Extensive comparisons of the findings of the model to results obtained by the electrogeometric model and also to a practical empirical formula are included.