The three main factors which can affect the health of the transformers are the paper, which is used for conductor insulation, the pressboard which is used for the major insulation and winding support and the insulating oil.
With age, water and contaminants (air or gas bubbles, particles of different origin, oxygen, and oil ageing) dissolve in the dielectric fluid of the transformer increasing the risk of failures or accelerating ageing of the insulation system, thus reducing the technical life. The level of possible contamination of the insulating oil over the years depends on its design, especially on the effectiveness of the oil preservation system, and sources of contamination.
By sampling and analyzing the dielectric fluid, the presence of contaminants can be detected and appropriate preventative actions initiated. The Oil and Gas Analysis remains a critical component of the condition assessment of the transformer.