Study of kc coefficient values established in the Brazilian and International Standards for Lightning Protection Systems

Abstract

This article presents a study on the values of the partitioning coefficient kc of the lightning current amongst the air-terminations/down-conductors, which depend on the type of air-termination system established by the Brazilian and International Standards for Lightning Protection Systems. For the present study, a model was developed by means of specific arrangements of inductive impedances for several specific configurations. However, the arrangements do not cover evaluations of electromagnetic couplings with installations or metallic parts inside structures or buildings. Such model is detailed throughout the paper. The methodology used converts the length of the conductor's air-terminations system and down-conductor into equivalent inductances. An equivalent circuit of inductive impedances was elaborated from the cited model. And from this, equations were synthesized, and tables where the shown kc values calculated from the modeling and compared with the values were simulated with the software ATPDraw 6.0. The values calculated by the equations established according to the mentioned standards. The obtained results converge between the values simulated and calculated by equations and have a significant deviation of up to 57% in relation to the values simulated by the equations of the standards mentioned, depending on the length of the down-conductors. Considering such information and considering that the safety distance or separation distance 's' is directly related to the ‘kc’ factor, the conclusion is to recommend an evaluation of the equations for the calculation of such factor. Thus, in our understanding, the safety distance will be more effective for mitigating dangerous sparks that could cause damage to people and structures.