The triangular arrangement of cables has the advantages of good magnetic field balance and compact structure, making it a commonly used arrangement in tunnel power cable lines. Accurate measurement of its current helps to make accurate judgment of the line operation status. However, the tunnel transmission method involves a complex line arrangement in a small space. Therefore, non-contact wide-range current measurement based on magnetic sensors is a better solution. In the face of uncertain magnetic interference in transmission tunnels, the use of magnetic shielding can suppress its effect on magnetic sensors. In this paper, an M-shaped magnetic shield structure is proposed for current measurement in a triangular arrangement with strong magnetic interference at random locations. Then, the thickness, position, axial length, gap width and location of the sensing areas of the structure were investigated. The effectiveness of the structure was verified by finite element analysis methods for measured currents of 200 to 2000 A. The structure was also validated by the finite element analysis method. The mean shielding uncertainty (MSU) of the shielding structure is verified to be 0.19% under the uncertainty of strong magnetic interference for a measured current of 2000 A. The M-shaped shielding structure is more resistant to interference than the C-shaped shielding structure and fits better into the triangular arrangement of the cable geometry.

triangular arrangement,non-contact measurement,magnetic shielding,mean shielding uncertainty