Unexpected failures in transformers led to the identification of copper sulphide
formation, deposited on the conductors. The qualitative presence evaluation of
corrosive sulfur in insulating mineral oil, led to a change in the Brazilian standards
ABNT NBR 10505, which assesses the presence of corrosive sulfur in mineral oil,
change in the time and test temperature to 150 °C / 48 hours. Performing the
chemical speciation of organosulfur compounds (by gas chromatography coupled to
mass spectrometry), were found 13 compounds in the Nynas oil and 9 compounds in
the Petrobras oil. DBDS, which was found only in the Nynas oil, and it was the
compound with the highest concentration. To perform the determination of the
presence of DBDS in insulating mineral oil, a method by gas chromatography
coupled to mass spectrometry was developed, and it was possible to quantify the
amount of DBDS in insulating mineral oil samples derived from the power
transformer. The passivation process by tolutriazol and benzotriazol, used as
anticorrosive additives in the core of electrical equipament, was evaluated; after a
while the effect of the addition of passivating agent becomes ineffective with time.
The solution for the remotionl of DBDS from mineral oil was realized by using carbon
nanotube reinforced by metallic matrix as agent to remove the DBDS. It was found
that the adsorption agent was able to realize the complete DBDS remotion from
insulating mineral oil up to a volume of 4000 mL (oil contaminated with DBD).
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