Repair or replace a transformer? Measured condition is what decides

The question usually arrives with the budget already on the table: a transformer has been in service for years, it starts giving trouble, and someone has to decide whether to invest in repairing it or replace it. Age alone does not answer that. Two units built the same year can be in opposite condition depending on the load they carried, the temperature they ran at, and how their insulation was maintained.

Measurement does answer it. A condition diagnosis combines tests on the electrical circuit — turns ratio, insulation resistance, power factor, winding resistance — with analysis of the fluid and the paper: dissolved gas analysis for internal activity, and furan analysis to estimate the degree of polymerisation of the insulating paper. That last figure is the one that separates investing from not investing, because the paper is the only component of a transformer you cannot replace without rewinding it.

In the documented oil change on a 2,000 kVA transformer, furans came back below the detection limit and the estimated degree of polymerisation was 800: sound insulating paper. A result like that supports continued investment in the unit. The opposite result argues against it, even if the transformer is running normally.

The diagnosis is delivered with the measured value, the criterion it was compared against and a verdict per unit. That is the document a maintenance team uses to defend the route in front of operations and procurement.