A group of 4 industrial transformers (25 MVA, 15/6 kV), in a petroleum refinery.
Installed on 1993, one of them has an electric failure on 2004.
The fault is later identified as due to corrosive sulfur (detachment of copper sulfide particles from naked copper, LV side, discharge to earth).
Meanwhile the manufacturer repairs the equipment, and refill it with the same naphtenic oil.
Copper sulfide on LV conductors
Controls on twin transformers (not failed) shows a general risk of corrosive sulfur
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Diagnosis on transformer fleet:
All oils are corrosive according to ASTM D 1275 A extended to 72 h.
All oils contains DBDS.
On the basis of the experienced failure and the high loading an high risk factor is identified for all the transformers of the same family.
Preventive action:Selective depolarization of the oils, to remove corrosive compounds.
Results:Before depolarization: 4a
After depolarization: 1b
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Diagnostic on fleet of similar transformers permits (often learning from previous failures) to prevent damages by operating specific actions/notizie |
