Monitoring a transformer comprising a tap changer

A method for monitoring a transformers comprising a tap changer, said transformer having at least two magnetically coupled windings and the tap changer having impedance elements (R1, R2) and a switch configured to gradually pass the impedance elements when changing between two tap changer positions (P1, P4) during a tap change operation, the method being performed in a protection device and comprising:

• obtaining waveforms of measured power transmission properties (Iin, Uin, Iout, Uout) recorded at the first and second transformer sides, said measured power transmission properties being currents and/or voltages,
• processing the recorded waveforms for obtaining at least one waveform representing a tap change operation, and
• extracting information (ODT, AMP) indicative of the health of the tap change from said at least one waveform that represents the tap change operation,
• wherein the extracted information includes an operation duration time (ODT) covering at least a part of the tap change operation and/or an amplitude (AMP) of said at least one waveform representing the tap change operation.

A computer program product for monitoring a transformer comprising a tap changer, said transformer having at least two magnetically coupled windings and the tap changer having impedance elements (R1, R2) and a switch configured to gradually pass the impedance elements when changing between two tap changer positions (P1, P4) during a tap change operation, the computer program product including a data carrier with computer program code configured to cause a waveform analyzer of a monitoring device to

• obtain waveforms of measured power transmission properties (Iin, Uin, Iout, Uout) recorded at the first and second transformer sides, said measured power transmission properties being currents and/or voltages,
• process the recorded waveforms for obtaining at least one waveform representing a tap change operation, and
• extract information (ODT, AMP) indicative of the health of the tap change from said at least one waveform that represents the tap change operation,
• wherein the extracted information includes an operation duration time (ODT) covering at least a part of the tap change operation and/or an amplitude (AMP) of said at least one waveform representing the tap change operation.