2.2.1 TEST METHOD
The thermal aging tests for BTA-added oil are conducted
by the same method as described in section 2.1.2. Octyl
sulfide and octyl sulfoxide are used. The concentrations of
sulfur compounds added are the same for all cases at 86 ppm
when converted to the sulfur concentrations. The
concentrations of BTA are zero, 10 and 34 ppm. The
amounts of pressboard are zero and 1/9 and 1/4 of the
amounts of insulating oil. The initial values of ECT of all
oils before the thermal aging tests are less than 100 pC/ml.
The ECT and the concentration of BTA in oil during the
thermal aging tests are measured. Table 2 summarizes the
test cases