Lightning Currents in DBS System from Triggered-lightning Experiments at Guangdong, China

This paper presents a statistical analysis of the characteristics of surge currents measured in a number of cables in a Distribution Base Station (DBS) system when being struck by rocket-triggered lightning. The measurements were conducted in the period from 2011 to 2013 at Guangdong, China. Lightning strikes were triggered through a 6.1m lightning rod at the top of a 15.2 m experimental metallic tower. The DBS equipment was installed partly on the platform near the tower top, and partly inside the cabinet on the ground level. There were some signal/power cables, RF feeder cables, and fibers applied for interconnecting the DBS equipment in both parts. The return-stroke current waveforms were recorded during the lightning current injecting into the metallic tower. Statistical information has been presented for the return-stroke peak current including the parameters of the risetime (10%-90%), the half-peak width, and the charge transfer. Our statistics on the return-stroke current peak are found generally in consistent with those reported from other triggered-lightning studies. In addition, the lightning currents shared into the number of cables were analyzed. The results show that a large part of the return-stroke current flow into the local earthing network through the tower metallic elements. Only a small part of the total injected current is shared into those cables. Next, with this specific or typical AC installation for DBS system, we have found the current level flowing into the AC power installation cables is much lower than the 50% of the total injected lighting current. This fact may remain us to re-consider if the assumption of 50% current sharing at AC installation cable by IEC standard [9] is too high.