For diagnosis of the “Corrosion caused by dissolution of metals (C4)” criticality, Sea Marconi uses its own diagnostic metrics, namely:
the visual signs of external observation of the transformer are interpreted, and those from any internal inspection after failure on twin machines;
by analysing the oil, the symptoms, that is, the specific indicators (e.g. dissolved copper), are identified;
For example, for a new transformer to be energised or after energisation, the typical concentration of copper dissolved in oil is “not detectable”, that is, < 0.1 mg/kg. For a transformer in operation instead, the reference value must be calculated on a statistical basis of the reference population at the 90th percentile (e.g.0.80 mg/kg)
the database is used to study family or subjective case histories in the search for failures in similar machines (same oil, same manufacturer, same type of equipment, same operating profile, similar age),
factors of uncertainty, speed and evolution over time (trend) for each symptomatic indicator are examined and monitored
on the basis of assessment of these key factors, specific criticalities are classified according to type and priority, and type and priority of corrective actions (treatments) are identified at the same time
