Experimental Assessment of the FDD and a Line Trap Mockup Effects on High-Frequency Overvoltages

This paper addresses the issue of protecting power facilities from high-frequency overvoltage pulses of lightning and switching origin. An experimental comparison of the effects of a Frequency-Dependent Device and a line trap mockup on MHz-range overvoltage pulses is presented. In contrast to previous studies, this work utilizes full-scale FDD samples and an LT mockup replicating the FDD design but without ferromagnetic and insulating layers. An improved measurement methodology was developed and tested, enabling the generation of steep-front pulses (simulating lightning/switching overvoltages). The results demonstrate that the FDD reduces the pulse front steepness 25 % more effectively than the LT mockup, owing to its ferromagnetic layer, which increases active resistance at high frequencies ($450-500 \Omega$ at $1.2-1.8 \text{MHz}$). These findings highlight the potential of FDDs for protecting power facilities from highfrequency overvoltages and provide a foundation for further research in the $10 \text{kHz}-5 \text{MHz}$ range. The work also revealed several nuances that could improve future high-frequency measurements.