Direct lightning strikes to the lightning protective system of aresidential building: triggered-lightning experiments

摘要

Lightning triggered from natural thunderclouds using thenrocket-and-wire technique was employed in order to subject to directnlightning strikes the lightning protective system of a test house at thenInternational Center for Lightning Research and Testing (ICLRT) at CampnBlanding, FL. The electrical circuit of the test house was connected tonthe secondary of a padmount distribution transformer located a distancenof about 50 m from the house. The transformer primary was connected to an650-m long unenergized underground power cable. The test house had twonground rods, one for the lightning protective system grounding and thenother for the power supply system grounding. The two rods were about 3 mnapart and were connected by a metallic cable. Lightning current wasninjected into the lightning protective system ground rod, and thencurrents and voltages at different points in the test system werenmeasured. The waveshapes of currents in the ground rods of the testnhouse differed markedly from the current waveshapes in other parts ofnthe overall system. The ground rods at the test house appeared to filternout the higher frequency components of the lightning current, allowingnthe lower frequency components of the current to enter the house'snelectrical circuit, that is, the ground rods appeared to exhibit ancapacitive behavior rather than the often expected resistive behavior.nThis effect was observed for DC grounding resistances of the rodsn(driven in sandy soil with conductivity of about 2.5×10-4n S/m) ranging from more than a thousand ohms to some tens of ohms.nThe peak values of (1) the current entering the test house's electricalncircuit, (2) the current flowing to the distribution transformernsecondary neutral, and (3) the current flowing through the surgenprotective devices at the test house's service entrance were observed tonbe greater than in either of the two scenarios suggested by thenInternational Electrotechnical Commission