For diagnosis of the “Corrosive sulphur from sulphur combustion by-products (C3)” criticality, Sea Marconi uses its own diagnostic metrics, namely:
visual signs on the transformer are interpreted, in this case following an inspection after failure of twin machines;
by analysing the oil, symptoms are identified, that is, specific indicators (Total Corrosive Sulfur);
|
Recommended DBDS value
|
Reference standard
|
|
|---|---|---|
| For new insulating oils | not detectable (< 5 mg/kg)” | [IEC 60296 Ed. 4-2012, table 2, page 17] |
| for insulating oils in operation – before energisation | “not detectable (< 5 mg/kg)” | [IEC 60422 Ed. 4-2013, table 3, page 24] |
| for insulating oils in operation – after energisation | (< 5 mg/Kg)” If the concentration of DBDS is greater than the recommended threshold, a risk assessment must be carried out and mitigating actions applied; table 5, note d – these include a selective depolarisation treatment to effectively remove corrosive sulfur from the oil 11. 4. 4. |
[IEC 60422 Ed. 4-2013, table 5, page 31] |
| for insulating oils in operation | (< 10 mg/Kg)” – in this case selective depolarisation to remove effectively from oils is also one of the mitigation techniques 4. 2 page 25 |
[CIGRE 378 Fig. 9 page 31] |
the database is used to study family or subjective case histories (in the search, for example, for failures in twin machines);
factors of uncertainty, speed and evolution over time (trend) for each symptomatic indicator are examined and monitored
