Heat-stability of mixtures of paraffinic transformer oil with alkylbenzene

Abstract

Effects of blending alkylbenzenes in a paraffinic base transformer oil were extensively investigated, paying particular attention to their influence upon its heat-stability. Oxidation stability tests of the oil specimens, tube aging tests of Kraft paper/oil electrical insulation systems for oil-filled transformer use and accelerated aging tests of the distribution transformers consisting mainly of the same electrical insulation systems were carried out and their test results were compared with those obtained by use of an actually used, naphthenic mineral oil for oil-filled transformers. It has been pointed out that blending the alkylbenzenes in a paraffinic base oil improves its pour point, gassing tendency and oxidation stability to some extent. As a result of the tube aging tests conducted in a closed nitrogen gas atmosphere it has been clarified that blending the alkylbenzene in a paraffinic base oil improves the degree of deterioration of the Kraft paper, although the paraffinic base oil appears more stable than the alkylbenzene blended one because of having difficult access to oxygen. Moreover, judging from the results of the accelerated heat-aging tests for the distribution transformers, it has been demonstrated that the dissipation factor of the alkylbenzene blended paraffinic oil increases less than that of the pure one along with the aging period, and that this tendency is definitely delineated by the aid of the relationship between the dissipation factor and the neutralization value of the oil specimens. Thus, it has been concluded-that the alkylbenzene blended paraffinic oil is considered an transformer oil equivalent to an actually used, naphthenic mineral oil.