Condition monitoring through regular oil sampling and analysis is a very important tool for increasing the availability, reliability, and lifetime of high-value assets.
The breakdown voltage (BDV) or dielectric strength of transformer oil is the maximum voltage for which the transformer oil remains its insulating property, withstanding the electric stress (voltage) without failure. Oils with high breakdown voltage are deemed good electrical insulators.
Above this BDV oil will no longer insulate and a breakdown will occur. Here we can see the exact moment it happens.
Contaminants such as water, sediment and conducting particles (dirt) reduce the breakdown voltage of insulating oil.
This technical interpretation is a very crucial aspect and on insulating oils it helps save many Transformers from failing.