초록
This study proposes a new method to estimate voltage unbalance more exactly using Thevenin's equivalent circuit. The conventional simple formula were easily applied to evaluate voltage unbalance. Because the formula was derived on the assumption that traction load would be directly connected to the secondary windings of the main transformer, they could not consider the detailed characteristics of traction power supply system, for example, self and mutual impedances of rail, catenary and return feeder. So, the ac쳐racy of the results could not be guaranteed. The proposed algorithm is applied to a standard autotransformer-fed test system to analyze unbalance phenomena. Through simulations, we could evaluate voltage and current unbalance factors and compare the voltage unbalance of the three transformer connection schemes : single phase, V- and Scott-connections which are required for suitable train operation schedules. Additionally, we could determine the combinations of trains which can be operated under the unbalance factor limits.