On-site diagnosis of power and special transformers

This paper deals-after a brief introduction to transformer life-management-with the difficult subject of condition assessment of transformers and the required or available diagnostic procedures. The On-site Diagnosis is achievable with a multitude of procedures if consequential approaches are taken. Equally important are the Fingerprints to characterize the initial status, the Periodic Check and or the On-Line Monitoring information. To date-except for a few special cases-on-site-diagnosis can verify: 1) dielectric failures in magnet circuits; 2) dielectric failures in windings and main insulation; 3) dielectric failures in bushings and tap changers; 4) failures due to dynamic impact; 5) failures due to critical thermal or dielectric aging. The particular diagnostic procedures for the individual perspectives are presented and discussed. The On-Line-Monitoring can as a sort of "early warning systems" offer great assistance and save tremendous costs. Therefore also the most promising On-Line-Monitoring procedures are discussed.