The addition of BTA is found to be effective for both
sulfide and sulfoxide compounds. BTA reacts with copper
catalyst, which enhances the oxidation in insulating oil. This
reaction inactivates the catalyst action, suppresses the
generation of peroxide and retards the conversion of sulfide to
sulfoxide. The hydrogen ion bonded to nitrogen in a BTA
molecule dissociates so that BTA exists in the oil in the form
of a positively charged hydrogen ion and a negatively charged
BTA ion. The hydrogen ion has low affinity to insulating oil
because of its small molecular size and move to the solid
insulator. On the other hand, the BTA ion remains in
insulating oil because of its high affinity to insulating oil,
which reflects the large molecular size. The negatively
charged BTA ion can mitigate the increase in ECT by
positively charged sulfonium ion.