New properties of "old" transformer materials

Paper, pressboard, mineral oil, copper have been used for decades in the power transformer design and are considered as "classic materials". Progress in the material technology, as well as reliability requirements for obtaining higher life expectancy require a better knowledge of their degradation pattern and additional information on their long term properties. The reliable diagnostics for an early failure recognition, as well as adequate maintenance procedures for restoring the dielectric margin are needed. These challenges can only be solved with a better knowledge on ageing processes and physico-chemical behaviour of transformer materials and their consideration in the transformer design.