Power quality study of fixed capacitor selection for rotary 1ph-3ph converters in rural facilities

A rotary-converter, commonly found in remote rural facilities, is a simple arrangement of an induction machine and a capacitor able to produce a three-phase voltage when connected to a single-phase system. Such resulting voltage can feed other three-phase equipment, but its quality depends on the capacitor and load characteristics, as well as the single-phase input voltage. To the authors knowledge, rotary converter component selection is mostly empirical as there is no publicly available document to formally design these systems. To address this issue, this paper first presents an analytic expression to select the capacitance value to minimize voltage unbalance, while taking into account its effect on the quality of power under load variations and harmonic distortions from the voltage supply. Quick reference tables are also presented to design the rotary converter motor size and capacitor depending on the load demand and power factor, as well as taking into account the theoretical limit of voltage unbalance and resulting harmonic resonance characteristics.