DEPENDENCE OF UNIFORM/NONUNIFORM FIELD TRANSFORMER OIL BREAKDOWN ON OIL COMPOSITION.

The 60-Hz and impulse breakdown characteristics of two oils, A and B, which differed markedly in needle-sphere (N-S) impulse strength were determined in uniform and divergent field geometries. Oil A, which had the higher N-S strength, was a commercial transformer oil, and Oil B was this same oil doped with anthracene. In the uniform field tests, the two oils had essentially equal bare electrode 60-Hz and impulse strengths and covered electrode 60-Hz strength. Oil B, the lower N-S strength oil, had a slightly higher covered electrode impulse strength. In weakly divergent fields, the 60-Hz breakdown and corona inception levels of Oil B were comparable or superior to those of Oil A. Impulse breakdown voltages were found to depend on oil composition and impulse polarity; however, these dependences varied with field divergence. The data suggest that the anthracene additive modified the divergent field breakdown initiation and streamer propagation processes in oil, and indicate a lack of correlation between the highly divergent field N-S test and the insulating characteristics of oils in uniform and weakly divergent fields.