Figure 10 points out the relationship between the molecular
weight and the ECT of various sulfide compounds in
accelerated aging tests. This figure shows the ECT in the test
Sulfide compounds are transformed into
sulfoxide compounds by reaction between sulfur elements and
peroxides. When the molecular weights of sulfide compounds
are large, the hydrocarbons on the side chains work as a steric
hindrance and the transformation reaction is disturbed. On the
other hand, high ECT compounds have a strong affinity with
insulating oil, exist stably in insulating oil and increase as time
passes if their molecular weights are near the molecular
weight of insulating oil (hydrocarbon molecules). The