Scenario
Brazilian energy transmission network of TSN e Novatrans with 76 electrical equipment filled with insulating fluids.
TSN
Substations 6
Total reactors 40
Reactors with corrosive sulfur 37 (92,5%)
Total failed reactors 15 (37,5%)
Novatrans
Substations 6
Total reactors 36
Reactors with corrosive sulfur 13 (36,11%)
Total failed reactors (-)
2005
Discovery of DBDS. Sea Marconi, first in the world, in July 2005 identifies the DBDS as the main responsible of the faults attributed to the “corrosive sulfur”.
2006
Sea Marconi laboratory confirms the presence of DBDS through instrument configuration (GC-AED), a real fingerprinting (fingerprint) of the oil.
This analytical technique showed that the naphthenic base oil Nynas Nitro GBN 10 contained DBDS. That oil was used inside the equipment affected by corrosive sulfur.
Today it is known that the DBDS tends to bind to copper and form copper sulfide Cu2S
2009
The solution was a campaign of selective depolarization treatments (Chedcos) by Sea Marconi. The treatments were performed on-site both off-load and on-load (transformer fully load during the treatment).
The Brazilian energy transmission network chose all the countermeasures available:
- replacing the corrosive oil with a new one not corrosive
- passivation with Irgamet 39
- selective depolarization treatment (Chedcos)
Chedcos® offers the advantage of preventing the operational criticalities correlated with the change of the oil that would be, in any case, contaminated by the DBDS present in the residual oil impregnating the papers. From the failure case history reported also by CIGRE 378 it results also that the passivator (e.g. Irgamet 39) does not eliminate the cause of the corrosion (the DBDS), it degrades in a few months and its protective action on the copper surfaces results being inhomogeneous and ineffective.
