Patent ID: 7961112

Claim:
A method for monitoring the condition of an electrical power transformer, the method comprising: a) measuring current and voltage data at terminals of the transformer, wherein the current and voltage data comprise both current and voltage data measured at terminals on a high voltage side of the transformer and current and voltage data measured at terminals on a low-voltage side of the transformer, wherein the measured current and voltage data do not contain injected test signals; b) computing from the measured current and voltage data corresponding transformer impedance data by i) calculating an initial solution by setting six cross impedances to zero and solving for three impedances from the measured current and voltage data; and ii) calculating nine complex impedances from the initial solution; c) repeating (a) and (b) continuously in real time to provide a temporal sequence of real-time transformer impedance data comprising the corresponding transformer impedance data; and d) calculating from the temporal sequence of real-time transformer impedance data a moving average of transformer impedance; and e) generating an alarm signal if recent transformer impedance values in the temporal sequence depart from the calculated moving average by a predetermined amount.