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 Z/sub t/ describes this undesired coupling. In a low-frequency circuit model, Z/sub t/ decomposes into two terms which vary with the cable length l and with l/sup 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 Z/sub t/ at the power frequency. Measurements confirm the model. With the low Z/sub t/, the direct capacitive coupling between the high-voltage arm and neighboring circuits showed up as a comparable interference source.