Sacrificially. Oxidation of the oil proceeds by a free-radical chain reaction, and the antioxidant, typically DBPC, interrupts that chain by donating a hydrogen atom to the radical and terminating it before it can propagate. While inhibitor remains, oxidation is held almost completely in check.
2
Why must inhibitor content be monitored?
Because it is consumed as it works, and once depleted the oil oxidises rapidly with little warning. Inhibitor content is therefore a routine condition-monitoring parameter alongside acidity, water content, breakdown voltage and dissolved gas analysis, and a declining trend is the signal to plan re-inhibition or oil replacement.
3
Can a transformer be re-inhibited?
Yes, adding inhibitor to oil in service is a recognised maintenance option and is considerably cheaper than replacing the charge. It is appropriate where the oil is otherwise in good condition, with acidity, water and dissolved gas within limits, and where the depletion has been identified before significant oxidation damage has occurred.
4
When is an inhibited oil the better choice?
In hot, heavily loaded transformers and in high ambient temperatures, where oxidation is fastest and the extended induction period of an inhibited oil gives materially longer service life. The trade-off is the monitoring obligation, since the protection depends on an additive that is being consumed rather than on the base oil itself.
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