Many existing studies on the magnetic flux leakage of broken strands in the steel core only consider geometric parameters such as length, width and depth of the broken strands, and the impact of the broken strand angle on the leakage field has rarely been discussed. Therefore, this paper establishes a 3D finite element model of a steel core magnetic flux leakage detection device to analyze the magnetic flux leakage vectors Bx, By and Bz under 12 different broken strand angle conditions. By comparing the three vectors, the vector direction which is most sensitive to detecting broken strand faults is obtained. The results show that vectors Bx and By exhibit multimodal distributions, and the distributions of positive and negative peaks are opposite with a 90° broken strand angle as the division point. Moreover, vector Bz exhibits multiple peaks at a 90° broken strand angle due to the influence of the broken strand width, while in other conditions Bz exhibits a single-peak distribution. The comparison of the vector peak values shows that the vectors Bx and By have similar positive and negative peak values under different operating conditions. The peak values of vector Bz significantly exceed that of Bx and By, with the largest difference observed at a 90° broken strand angle. The positive peak values of Bx and By are only 4.5% and 2.2% of the positive peak value of Bz, and the absolute values of the negative peaks are only 1.5% and 2.9% of the positive peak value of Bz. Vector Bz proves to be the most sensitive in detecting broken strands of the steel core. Consequently, Hall elements should be arranged perpendicular to the transmission line surface to detect vector Bz as the most effective signal detection scheme.