Abstract
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.
Highlights
C ONTACTLESS transducers of dc electric currents often have magnetic yoke, which concentrates the flux generated by the measured current
The yoke shields against external magnetic fields, including those caused by external currents [1]
Chen and Chen [9] used four Hall sensors on each conductor and measured errors caused by external currents
Summary
C ONTACTLESS transducers of dc electric currents often have magnetic yoke, which concentrates the flux generated by the measured current. George suggested to suppress the influence of the measured conductor position by calculating B1× B2/(B1+ B2) [8] This trick would destroy the immunity of the differential transducer against external currents. Chen and Chen [9] used four Hall sensors on each conductor and measured errors caused by external currents They found that the difference between calculated and measured errors was below 6% for conductors in the close vicinity, and this difference is rapidly decreasing with an increase in distance between conductors. Circular sensor array with more than four sensors around the conductor approximates better the closed line integral in Ampere’s law This brings better immunity against the position of the measured conductor [10] as well as against the crosstalk from external conductors [11]. We start with the analytical calculation of the influence of the idealized current, follow with Finite Element Method (FEM) simulation of the real conductor, including the effects of the eddy currents and finish by the experimental verification of selected configurations
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