Power quality assessment of single-phase induction motors under voltage unbalance conditions

Do minor voltage fluctuations really matter for small motors? The answer carries significant implications for the millions of single-phase induction motors operating in residential, commercial, and light industrial applications throughout New Zealand's distribution networks. This research quantified performance degradation in single-phase induction motors subjected to controlled voltage unbalance conditions ranging from 0% to 6% voltage unbalance factor at the Power Systems Laboratory of Wellington Institute of Technology between May and September 2024. Three motor ratings (0.75 kW, 1.5 kW, and 2.2 kW) commonly found in pumping, ventilation, and small machinery applications were evaluated under standardized loading conditions. Measurements captured efficiency, power factor, current harmonic distortion, and thermal characteristics across the unbalance spectrum. Results demonstrated that even modest 2% voltage unbalance reduced motor efficiency by 2.8-3.6 percentage points and elevated current total harmonic distortion from baseline values of 4.8% to 8.3%. At 6% unbalance, efficiency losses reached 9.2-10.8 percentage points with current THD approaching 19.4%. Temperature rise measurements indicated accelerated thermal stress under unbalanced conditions, with winding temperatures increasing 12-18 °C above balanced operation levels. These findings support stricter voltage quality monitoring at distribution level and inform equipment specification decisions for installations prone to supply imbalance.