Influence of dc and dc/ac composite fields on the flow electrification characteristics of transformer oil

Abstract

Flow electrification characteristics of transformer oil were investigated by applying dc and dc/ac composite fields to both bare and covered coaxial cylinder electrode systems. For the bare electrode system, flow electrification characteristics were almost the same between positive and negative dc voltage applications and negative charges were generated for both dc and dc/ac composite voltage applications at high dc fields. For the covered electrode system, the apparent flow electrification characteristics differed between positive and negative dc voltage applications. For the former, negative charges were generated at high dc fields for both dc and dc/ac composite voltage applications, and for the latter, positive charges were always generated for both voltage applications. However, negative charge generation for the positive voltage application was attributed to the influence of negative charge generation at the bare part of the covered electrode end; the fundamental charge generation characteristics of the covered electrode showed an increase of positive charge generation by dc voltage application, and positive charge generation was accelerated by a composite ac field. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 10-17