On-line monitoring of electrodynamic effects on power transformers windings

A strategy for protecting power transformers, based on the possibility of taking measurements on machines under real operating conditions, is discussed. A measurement technique for determining the online variations of stray reactance of transformers due to short-circuit events is reported. This parameter can be indicative of winding geometry; hence it makes possible the setting up a diagnostic system that provides useful indications of conductor insulation reliability. This method is suitable, with the proper choice of measuring device constants, not only for identifying core and winding losses, but also for determining the changes of short-circuit reactance of the transformer