ABSTRACT be corrosive or non-corrosive to the copper

 

ABSTRACT

 

Mineral
oil is used as both coolant as well as Electrical insulator in Transformers,
Reactors, etc. It is obtained from fractional distillation of crude oil in a
petroleum refinery which basically contains naphthenic and paraffinic groups
along with some impurities. These impurities include different forms of sulfur
which might be corrosive or non-corrosive to the copper windings present in the
transformer depending on the structure of the compound.

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Dibenzyl
Disulfide (DBDS)  is used as a anti
oxidising agent in transformer oil in PPM level.   DBDS  is one of such corrosive compound which is
stable at normal temperatures but reactive at higher temperatures. This
corrosive reaction can be prevented by adding additives which form a protective
layer around the copper. This phenomenon is known as passivation and the
additive added is known as passivator. One such passivation is Irgamet®
39
which is a derivative of Benzotriazole (BTA). In the experiments on mineral oil
with DBDS alone and DBDS along with Irgamet® 39
at concentrations of 100ppm are performed at different ageing times of 6, 12,
24, 48 and 96 hrs at an elevated temperature of 1400C.
The above is repeated for varying exposure of mineral oil to the copper
obtained by increasing number of strips and covering the strips with insulating
paper.

The
experiment was conducted to check di electric parameter like leakage current
and breakdown capability in each cases.These studies show the inefficiency of
insulating paper in transport limitation of the reaction between copper and
DBDS but efficiency of Irgamet® 39 in passivation
the reaction.  We can see the improvement
in dielectric parameters. Initial effectiveness of Irgamet®
39
is lost at long ageing times because of equilibrium reached for maximum
concentration of copper dissolving in spite of passivation recommending
replenishment of Irgamet® 39 after usages at high
temperatures for preventing corrosion of copper.