| Triggered-lightning experiments were conducted in 1996, 1999, and 2000 to study the responses of overhead power distribution lines to lightning at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida. The lightning was artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique, and its current was directed to a phase conductor at midspan or at a pole near the center of the line. Experimental results and associated EMTP modeling are presented in this dissertation for the following line configurations: (1) a two-conductor, 740-m overhead distribution line with 2 arrester stations in 1996; (2) a four-conductor, 245-m overhead distribution line with 2 arrester stations in 1999; and (3) a four-conductor, 829-m overhead distribution line with 6 arrester stations in 2000. The three-phase lines tested in 1999 and 2000 were standard designs of a major Florida power company. Lightning peak currents injected into the lines ranged from 7 to 57 kA. Voltages and currents were measured at various locations along the line. Video and photographic cameras were used to image lightning channels and detect line flashovers.; The significant results of the research are (1) flashovers between conductors were observed, both accompanied and not accompanied by arrester failures, (2) an arrester failed on seven of eight direct lightning strikes to the line in 2000, (3) arcing between conductors may prevent failures of arresters connected to the struck phase, (4) the bulk of the lightning current flows from the struck phase to neutral through the arresters closest to the strike point, (5) the withstand energy of the arresters can be exceeded due to the contribution from multiple strokes and/or relatively low-level, long-lasting current components, (6) the distribution of charge transferred to ground among multiple neutral grounds, which is determined by low-frequency, low-current grounding resistances is different from the distribution of peak currents to ground, which is characterized by a rapid decrease of current with increasing distance from the strike point, (7) EMTP allows one to model the observed line behavior with reasonable accuracy, (8) overall, the standard lightning protection of the distribution lines tested does not appear to be adequate. |
