Interpretation of results obtained from testing of oil filled electrical power transformers in field for several utilities in the world

This paper will shed some light on the recent results collected while testing several transformers for utilities around the world using the recently developed Fault Diagnostic Device for Electrical Power Transformers (FD²-EPT) by the first author and presently available commercially and used successfully by the second author at Ontario Hydro. The results obtained cover a wide range of transformers tested since December 1995 to November 1997 by the authors either individually or as a team, covering a volt-amp rating from 5 MVA to as high as 750 MVA, both in the single and three phase configurations. The single phase transformers were common in the 340 MVA rating. The voltage rating extended from 4.8 kV to 500 kV. The categories of transformers tested fell under: (1) distribution, (2) substation, (3) generator start-up, (4) unit transformers, (5)system service transformers and (6) rectifier transformers. The results obtained are primarily of the partial discharge (PD) type, however further validation of the results may indicate some other kind of incipient fault. A database of signals collected for several situations will be discussed and an attempt at making a base line interpretation for such signals will be enumerated using several examples. This data was also collected to generate the standards for the IEEE user´s guide for such a device. The first author is also a member of the working group of the IEEE Transformer Committee working on such a users guide