A method of detecting partial corona discharge in a targeted circuit of an electrical apparatus, comprises the steps of: wrapping a Rogowski coil around a leg of the targeted circuit to produce a Rogowski coil signal that represents electrical current rate of change in the leg of the targeted circuit; coupling the Rogowski coil signal to a three-dimensional display device that may represent the dimension of time, the dimension of amplitude as a function of a time, and the dimension of duration of amplitude as a function of time in successive periods of that have a preselected duration; monitoring the display device to detect deviations of the duration of amplitude as a function of time from a normal waveform in the leg of the targeted circuit; and correlating ones of the detected deviations of the duration of amplitude as a function of time from a normal waveform that exceed a preselected deviation level as indicative of partial corona discharge within the targeted circuit.