Technological progress continues to advance, particularly in the field of active components such as semiconductors. This progress has enabled us to reduce the size and weight of traction inverters for railway vehicles. On the other hand, problems remain with passive components such as reactors. In particular, onboard reactors are required to be considered not only as reactor units but also as part of a whole trainset. Therefore, as a determining factor, it is essential for reactors to be small and light. This paper focuses on problems such as flux leakage and resonance, which are unintentionally caused by onboard reactors, and explains changes in inductance values of reactors, so that this investigation informs further investigations.