Design and experimental verification of an isolated voltage probe for the 2 kHz–30 MHz interval operating in live conditions

The work discusses the different options for RF voltage measurement in LV grids (both AC and DC) used to evaluate distortion and conducted emissions over an extended frequency range (0.002 MHz to 30 MHz). Important characteristics are galvanic insulation, fundamental suppression and decent sensitivity, to guarantee safety and to allow the connection of sensitive measuring equipment. The design and experimental verification of a prototype based on a controlled-impedance branch, whose current is measured clamping an insulated RF probe on a number of turns, are reported. The results show that attenuation of only 24 dB is achievable, with a significant mains fundamental attenuation larger than 20000. The high-frequency behaviour was trimmed by adding ferrite beads to some selected turns achieving a flat frequency response within +/- 0.1 dB up to the-3 dB point at 31 MHz.