Development of unbalanced voltage estimation method using sensor switches for enhancing HC

After the implementation of FIT (Feed-in Tariff), photovoltaic systems (PVs) mainly are introduced to houses connected to low-voltage systems in Japan. These PVs are installed in the power distribution system through each pole-transformer that is one of single-phase transformers. Phase currents from PVs installed in low voltage systems cause unbalanced line-voltages and unbalance factor increasing. It is difficult that unbalanced three-phase voltages are controlled by OLTCs in the distribution system as a difference between minimum and maximum of three-phase voltages is expanding. DSOs is necessary to estimate the unbalanced three-phase voltages before the installation of PVs, and DSOs improve the unbalanced factor that cause voltage deviations from the specified range. To estimate the unbalanced line-voltage, author proposes an estimation method by the measured data from switch with VCT sensors and facility information acquired by DSO. The proposed method estimate a width of unbalanced line-voltages by both a positive voltage calculated by the facility data in the power distribution system and each line-voltage satisfying with an unbalanced factor defined by DSO and the calculated positive voltage. It was verified that the proposed method was effective to the estimation for the width of the unbalanced voltage by the test data.