1. A computer implemented method for characterizing a device that operated to clear a fault in a power distribution system feeder, the method comprising: measuring, by an Intelligent Electronic Device (IED) connected to the feeder, a current along the feeder proximate a substation bus; sending measured data corresponding to the measured current to at least one computer processor; and receiving from the at least one computer processor a most probable device size for the device that operated to clear the fault, wherein the at least one computer processor is configured to: determine from the measured data that the fault has occurred in at least one phase and has been cleared; subtract reference data from the measured data to estimate residual fault data; after the device operated to clear the fault, estimate from the residual fault data an operating point for the device that operated to clear the fault; calculate density functions for a plurality of device sizes; calculate for the operating point a proximity measure for each of the plurality of device sizes; and identify the one of the plurality of device sizes corresponding to the smallest proximity measure as the most probable device size for the device that operated to clear the fault.