Transformer insulation on the threshold of new era

Power transformers are reliable high performance electrical machines. The reliability of the power transformer is directly linked to the electrical insulation reliability. Well known and long time used paper-oil insulation system stands on the threshold of a new era. Due to the international agreements and environmental requirements it is compulsion to substitute petroleum based oils with synthetics or vegetable fluids. This brings us to the problem of the new insulating fluids diagnostics under various stresses. What are the differences between petroleum-based and new insulating systems is the main topic of the paper.