Overvoltages Induced in Loops with Disconnected Conductors

This article presents studies of voltages induced by lightning in conductive loops with disconnected terminals. The loop models used were formed by a conductor installed in cable trays located under or close to lightning protection systems - LPS. For the LPS, two models were analyzed: a wire air termination system and a vertical air termination rod. The induced voltages were computed using the waveforms established by the standards for the negative first strokes and subsequent strokes. To calculate the currents distributed by the wire air termination system, an equation was synthesized to determine the kc - current partition coefficient - as a function of the distance from the point of stroke of the lightning at the wire air termination. The results of the investigation indicated that depending on the configuration and dimensions of the loop in relation to the LPS of the captor cable type three results were obtained: one in which the LPS provides shielding to the installation; another in which it only attenuates the induced voltage, but with a characteristic form of shielding and another in which the overvoltage grows depending on the point of impact. When the LPS is the vertical air termination rod, no effect is observed that can be related like the shielding of the installations. In all cases the overvoltage has an increase, which can be up to 428% in relation to the same configuration of the wire air termination system. Another evidence observed for the isolated LPS, in the topologies studied, was that the angle of the loop in relation to a horizontal reference line passing through the base of the mast of the air termination rod has little influence on the induced voltages. The paper also discussed how this subject is addressed in the standards for lightning protection, related to physical damage to structures and life hazard.