Analysis and Determination of Three-Phase Unbalance Limit for Power Transformers Based on Simulation Modeling

Three-phase unbalance in power transformers is a prevalent issue that can cause overheating, reduce operational efficiency, and potentially lead to equipment failure. This paper introduces a novel approach for determining the acceptable limits of three-phase current unbalance in power transformers. The proposed method involves adjusting the load resistance of one phase within a three-phase imbalance simulation model, followed by analyzing the resulting simulation data, which includes neutral-to-ground voltage, secondary-side three-phase voltage, current measurements, and the degree of current unbalance. By applying curve-fitting techniques to this data and accounting for neutralpoint voltage and voltage quality, the unbalance threshold is established. This method offers an accurate means of determining the permissible current unbalance under varying load conditions, improving transformer reliability by mitigating excessive heat buildup and extending equipment lifespan. Additionally, it ensures compliance with power quality standards and provides grid operators with a practical tool for optimizing transformer load management across diverse operating conditions.