The spontaneous ionic purification phenomenon of transformer oil: Presentation and consequences

Experiments performed on different oils from in service transformers show that the conductivity of these oils can significantly decrease as a function of the time elapsed from the instant at which the test cell was filled up. Material for a characterization of this phenomenon – called “spontaneous ionic purification phenomenon” – is presented and a route for interpretation is proposed. The consequences of this phenomenon on the oil characterization are examinated.