Optimized Coil Arrangement in Wound Interphase Reactors for High-Power Rectifier Systems

This paper investigates the optimal arrangement of the coils in a wound-type interphase reactor to avoid the decreased inductance due to local saturation in the core when operated with high dc current. In theory, the direct currents and the related magnetomotive forces in the two ways of an interphase reactor are equal, and this compensation leads one to conclude that the global flux in the yokes is zero. However, the dc currents in the coils produce a significant leakage flux that flows locally in the core. If the coils are not suitably arranged and if the dc current is high, the leakage flux causes local saturation, a drop in the inductance, and noticeable circulation of a triple harmonic current through the reactor. Such a phenomenon is investigated by means of both a simplified field model and three-dimensional magnetostatic simulations. A number of criteria for the arrangement of the coils to improve operation are derived and applied to a real rectification system used in an electrolysis plant. Some in situ operational measurements of both the original and the improved interphase reactor are reported.