Power transformers are critical, capital-intensive assets for utilities and industry. Transformers are extremely reliable; however, many of the transformers in use today have already exceeded their design life. Today transformers are not automatically replaced, if they have reached the end of their life span, but left in service as long as possible. In contradiction to the past power transformers are operated nowadays at or above rated power. This accelerates the ageing process of the inner insulation, particularly of the insulation paper, which cannot be easily replaced. Investments of new transformers have to be planed in advance because big transformers cannot be bought ready made from the factory. For a systematic replacement and to avoid unexpected breakdowns diagnostic tools are more and more important.
Reliable assessment of the ageing state of high voltage power transformers is a basic condition for a fail safe and cost-saving service.
The paper gives an overview about the latest measuring technologies and contains interesting case studies for successful insulation diagnosis and fault locations in power transformers.
