EIOS T2-U Electrical Insulating Oil — Frequently Asked Questions

That no synthetic antioxidant has been added. The oil relies on the natural sulphur and aromatic inhibitors that survive refining to resist oxidation, rather than on a dosed additive such as DBPC. It is a recognised category under IEC 60296 and is specified by utilities and standards that have historically preferred it.

Because it degrades gradually and predictably rather than falling off sharply once an additive is exhausted. An inhibited oil is well protected until the inhibitor is consumed, after which oxidation accelerates with limited warning. Some utilities prefer the more linear ageing behaviour of uninhibited oil for long-life transformer populations where monitoring intervals are long.

Because the oxidation products cause the damage. They are polar and conductive, which degrades insulating performance, and they form sludge that blocks cooling ducts and reduces heat transfer. The acids produced also attack the cellulose paper insulation, and it is the condition of that paper, not the oil, that ultimately determines transformer life.

Not without compatibility testing. The two have different ageing characteristics and additive chemistry, and mixing can produce unpredictable oxidation behaviour and sludging. Where a top-up or a change of oil type is being considered, compatibility should be established by laboratory testing before the oils are combined in a transformer.