Analysis of radicals and copper(I) ion formed in initial oxidation stage of insulating oils.
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Initial oxidation of insulating oil catalyzed with copper metal shows a phenomenon in which the dissipation factor (tan δ) has a temporal increase (Fig. 1).We investigated this phenomenon through analysis of radicals and copper(I) ion formed during the initial oxidation. Electron spin resonance spectra using spin trapping technique revealed the manner in which radicals were generated when insulating oils were oxidized with or without copper. The rate of generation of radicals reached maximum at about 1h of heating (Fig. 3), and this result offers the proposition that this maximum agrees with the increase in tan δ.Comparison with different kinds of oils is also shown in Fig. 3. Generation of radicals differed significantly for each oil, and for the easily oxidizable oil, treatments by clay filtration or sulfuric acid extraction were effective to suppress the generation of radicals in the oil.Comparison of effects of copper compounds is shown in Fig. 4. Copper metal and cuprous oxide clearly promoted generation of radicals but cupric oxide was less active.Neocuproine complexation method was applied to determine specifically the concentration of copper(I) ion in oxidized oil (Table 3). The concentration of copper(I) ion in 45min-heated oil was higher than before or after the heating.These results and Fig. 2 suggest that dissolution of copper occurs as copper(I) ion and also increases as the temporal tan δ increases.DPPH draws out active hydrogen from a hydrocarbon molecule, and is then decomposed. The rate of decomposition of DPPH, therefore, should be proportional to susceptibility of oxidation initiated by drawing hydrogen. But Fig. 6 shows that the stable insulating oil B decomposes DPPH more rapidly than the oxidizable oil A does. This result suggests that another process acts in oxidation catalyzed with copper.Finally we conclude that the behaviour of copper(I) ion with generation of radicals would strongly relate to increase of temporal tan δ in initial oxidation.
- 公益社団法人 石油学会の論文
公益社団法人 石油学会 | 論文
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