Systems, devices, and methods for a transformer including: a first drive winding (206) wound on a first core; a second drive winding wound on a second core; a sense winding wound across the first and second cores; and a compensation winding wound across the first and second cores; where one or more utility lines are threaded through a middle of the first and second cores, a common mode current in the one or more utility lines causes one or more pulses to appear on the sense winding, a current on the compensation winding is adjusted until the one or more pulses on the sense winding are cancelled out, and the common mode current on the one or more utility lines is the adjusted current on the compensation winding multiplied by a turn ratio between the compensation winding and the sense winding.