Derivation and Enhancement of Hosting Capacity Considering Three-Phase Voltage Unbalance in Distribution System

In this study, we first conducted voltage measurements using sensor switches installed on actual distribution systems within our service area and investigated the causes of three-phase unbalance. From the measurement results on clear and rainy days, we confirmed that, in addition to the concentration of PV near feeder ends, the long feeder span and the effects of non-uniform mutual reactance arising from conductor configuration contribute to the expansion of three-phase voltage unbalance. Next, because deriving hosting capacity under three-phase voltage unbalance requires simulations that reproduce the observed unbalance trends, we performed simulations utilizing our equipment records and measurement data. As a result, we verified that the order of magnitudes among line-to-line voltages and the timing of voltage changes matched the field measurements, and that the trend in the three-phase voltage unbalance rate was successfully reproduced. Finally, using these simulation results, we calculated the hosting capacity under three-phase unbalanced conditions and demonstrated that modifying the connection phases of single-phase transformers to mitigate unbalance can lead to an increase in hosting capacity.