Mitigation of ground loop effects in high-voltage measurements

Ground loops can affect voltage measurement systems, in particular those in high-power test circuits. The net or common-mode current through the signal cable shield induces interference in the signal circuit. A generalized transfer impedance Zt describes this undesired coupling. In a low-frequency circuit model, Zt decomposes into two terms which vary with the cable length l and with l 2 respectively. Several divider setups are discussed; all employ the same high-voltage arm. The position and composition of the low-voltage arm vary. A proper design of the signal circuit ensures a low Zt at the power frequency. Measurements confirm the model. With the low Zt, the direct capacitive coupling between the high-voltage arm and neighboring circuits showed up as a comparable interference source