Influence of External Current on Yokeless Electric Current Transducers

Yokeless electric current transducers have compact size, but they are sensitive to external magnetic fields, including those caused by electric currents in their vicinity. It is often believed that this unwanted sensitivity can be effectively suppressed by using a differential sensor. In this paper, we investigate the effect of external current with arbitrary position on busbar differential current sensor. We show the main disadvantage of the differential current sensor: increased sensitivity to currents in the transversal direction, which are not sensed by a single sensor. We analyze by finite element method simulation also the influence of real conductor size and uneven density of ac currents. The results were verified on 1000 A current transducer using a pair of microfluxgate sensors. The realistic suppression of close currents depends on the conductor angular position and in 10 cm distance it can be as low as 50, but it can be corrected if the geometry is known.