Transformer connection phase determination device and method

A transformer connection phase determination device includes a processor that executes a procedure includes: acquiring a power value consumed by at least one consumer connected to a transformer connected to any phase corresponding to a combination of two of a plurality of distribution lines, and acquiring respective current values flowing in each of the plurality of distribution lines, in association with a time axis; applying a filter that attenuates low frequency components in a current value caused by the power value and in the respective current values flowing in the plurality of respective power distribution lines; computing respective correlation values indicating correlation between the current values caused by the power values to which the filter has been applied, and the respective current values flowing in the plurality of respective power distribution lines to which the filter has been applied; and determining the phase that the transformer is connected to.