Behavior of Oil Corona and Damage of Transformer Insulation

The, behavior of corona and the resulting damage in oil-filled insulation were investigated. internal corona should be divided into intrinsic oil corona and bubble corona. The former is far more intense than air corona. The magnitude of the individual charge usually exceeds 1 x 104 pC. Insulation damage barely appears under lx 105 pC. This fact was deduced from investigations of insulation models and experience with actual transformers. With some margin, a charge in excess of 1 x 104 pC can be expected to produce damaging corona. This work will be helpful in interpreting corona test results, as well as in improving procedures for testing corona in EHV transformer´s. Some proposals for testing transformers for the presence of corona are presented.