Recently, as interest in eco-friendly distributed power has increased, studies on the improvement of the performance of breakers such as DC breakers and on the reliability of existing AC breakers have been actively conducted. To improve the performance and reliability of these breakers, this paper conducted the analysis of characteristics of a low voltage circuit breaker using an external magnetic field. In this experiment, before the current-zero point, the cut-off time to improve the breaker performance is shortened and after the current-zero point, re-ignition, which is associated with reliability, is suppressed. According to the experimental results, the short-circuit characteristics before current-zero show a significant difference of 0.13 ms in the t₂₁ section, and the dielectric recovery strength after current-zero shows a 13.3% performance improvement in the latter half of the DRV (dielectric recovery voltage) V-t curve. This result has significant meaning because it can be easily improved under the control of the external magnetic field. Hence, it can be applied to the interruption performance improvement of breakers through detailed research in the future.

Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, and, in particular, ferrite permanent magnets often utilize spoke-type structures, which are magnetic flux concentrators, to compensate for their low coercivity and residual flux density. However, in general, spoke-type PMSMs do not use much reluctance torque, so double-layer spoke-type PMSMs have been studied for their more efficient design. Unlike general spoke-type PMSMs, double-layer spoke-type PMSMs can utilize high reluctance torque by increasing the difference between d-axis and q-axis reluctance. However, as the difference in magnetic resistance increases, vibration and noise are generated, which adversely affects the mechanical part and shortens the life of the motor. Although this problem seemed to be solved by applying core skew in the previous study, it was confirmed that the axial force caused by the axial leakage flux occurred in the maximum torque per ampere (MTPA) control section and the torque ripple was increased. Therefore, in this paper, a model that can apply symmetrical core skew and reduce axial force is proposed. First, the causes of the axial force generated in previous studies were analyzed. Based on the analysis of these causes, a new symmetrical core skew structure was proposed, and its justification was verified through FEA.