Temperature, oil brand and atmosphere were found to be
affecting factors of the copper sulfide deposition on the
insulating paper [12]. The copper sulfide deposition on the
insulating paper was found to be accelerated by the
existence of oxygen in atmosphere [13]. Recently, copper
sulfide deposition on the insulating paper was found to be
accelerated by 2,6-di-tert-butyl-p-cresol (DBPC) and
paraffinic hydrocarbons in insulating oils [14]. It was
considered that Cu-DBDS complex and Cu-DBPC complex
were formed in insulating oils with DBDS and DBPC
contained, and Cu-DBPC complex was considerably
affected copper sulfide deposition on insulating papers
[14]. Also, the weight of copper sulfide deposition on
insulating papers increased with the increasing
concentration of paraffinic hydrocarbon in insulating oils
[14]. The first objective of this study is to make clear the
influence of oxygen and DBPC on the copper sulfide
deposition on the insulating paper by the heating tests
stipulated by IEC 62535. Furthermore, deposits on the
insulating papers after the heating tests were analyzed by
energy dispersive X-ray spectroscopy (EDX) [3, 13, 15].
EDX is widely used to investigate constituent elements in
materials, but the deposits cannot be identified by EDX.
The secondary objective of this study is to clarify the
chemical structures of the deposits on the insulating paper
by X-ray absorption near edge structure (XANES), which
is a bulk-sensitive method to characterize the local atomic
arrangements around the X-ray absorbent element [16]