Figure 3 shows SEM images and EDX spectra of deposits
on the insulating papers after the heating tests in oil A
(DBPC free). In N2 atmosphere, copper was slightly
detected, and deposits were hardly observed on the
insulating paper. Whereas in N2 + 20%O2 atmosphere,
copper and sulfur were detected, and deposits of smaller
than 1 μ m diameter were observed on the insulating paper.
Figure 4 shows SEM images and EDX spectra of deposits
on the insulating papers after the heating tests in oil B (with
DBPC). In N2 atmosphere, copper was slightly detected,
and deposits were observed on the insulating paper.
Whereas in N2 + 20%O2 atmosphere, copper and sulfur
were remarkably detected, and deposits of smaller than
1 μ m were observed on the insulating paper.