A method for detecting non-technical losses in an electrical power system includes measuring an area under a squared RMS current curve for a power cable in the electrical power system over at least one time interval, measuring an active and a reactive energy for the power cable over the at least one time interval, and characterizing a cable reactance and a cable resistance using the active energy, the reactive energy, and the area under the squared RMS current curve. The method further includes determining an active energy loss and a reactive energy loss over the at least one time interval using the area under the squared RMS current curve and the reactance and the resistance of the cable, and detecting a non-technical loss in the electrical power system based on the active energy loss and the reactive energy loss over the at least one time interval.