High frequency earthing impedance measurements at Camp Blanding, Florida

This paper discusses the results of high frequency earthing impedance measurements made on the earthing systems installed at Camp Blanding, Florida. Much of the initial information used to confirm the results obtained from high frequency earthing impedance testers is based on comparison of measured data from specifically designed earthing systems with simulations of the expected response of the grounding system. More recently, testing using devices injecting a surge current into a grounding system was compared with earthing impedance testers measuring selected frequencies of up to 1 MHz. It was found that these devices yielded similar results. The impedance measurements at Camp Blanding were compared with currents measured during triggered lightning testing conducted in 2004 and 2005. Even though the dry porous sand at the site made the measurements difficult and the earthing impedance measurements were made four years and longer after system installation and current measurements, correlation was also found between the measured impedance and the measured current distribution.