Separation Distance Versus Induced Voltages

This article presents a study related on the overvoltages that appear across the separation distance between loops formed by conductive parts of a structure or of an installation and lightning protection systems - LPS, when the second is struck by lightning. The models of the loops studied were like those considered in the Brazilian and International Standards that establish the criteria and parameters so that the separation distances to be observed in projects of LPS are effective. The methodology consisted of modeling the LPS composed of down conductors and air termination mesh in inductive impedances, which were used for simulations in Soft ATPDraw 6.0. To simulate the lightning strike, the Heidler source incorporated in the soft was used. This allowed simulating and measuring the circulating currents in the inductive impedance diagram and thus calculating the overvoltages that appear in the separation distances of the loops, resulting from their mutual inductances. The evaluation of the probability of occurrence of sparking was carried out by means of the interpolation of curves in a graph representing the breakdown voltage for an air gap between rods in air, as a function of the duration of the impulse above Uo, for different distances of the air gap d. The results indicated that in some configurations dangerous sparks may occur or with a marginal possibility of occurrence, since the separation distance values calculated by this methodology are of the order of magnitude limit for those calculated according to criteria and parameters established in the Standards. This finding points to the need for some issues to need to be clarified.