The assessment of deteriorating level of transformer oil by (A) ferrographic technique and (B) thermal ageing failure data

The qualitative characteristics of transformer oil plays an important role in evaluating the working performance of transformers. The most predominant factors responsible for causing deterioration of transformer oil and subsequently failure of transformers are: 1) Development of internal pressure in the oil. 2) The rise in temperature during operating conditions. 3) Frequent change in operating voltage levels. 4) Rapid deterioration of solid insulating materials such as laminated paper, press board, various kinds of paper/cloth, both electrically and mechanically. The above mentioned causes of deterioration of oil directly or indirectly affect the working condition of the transformers in the field. This paper illustrates the assessment of deterioration level of transformer oil by ferro-graphic technique and thermal ageing failure data.