Evaluation and suppression of flow electrification of paraffinic based transformer oil

About a dozen field failures of very large (UHV) forced oil-cooled power transformers had been attributed to flow electrification of transformer oil. During the flow of hydrocarbon insulating oil through cellulosic insulation ducts in transformer, charge separation occurs at the interface of cellulose and oil. The negative ions accumulated on the cellulose may lead to dielectric breakdown in oil or at the interface. Considerable work is being done on this subject since last one decade. Now research activities are focused broadly on three fronts. First on standardization of measurement techniques, identification of affecting parameters and finally suppression up to safe limit. Most of the studies done so far have been on naphthanic based transformer oil. In this study an attempt has been made to evaluate paraffinic based transformer oil and study the effect of different parameters´ e.g., type and quantity of paper, mounting position of paper, etc. on charge density. Although not much significance is given to electrical resistivity of oil in various international specifications, an interesting relationship is observed here with charge density. Mitigation of charge density by adding BTA (Benzotriazol) and LAB (Linear alkyl benzene) is found satisfactory without affecting oil characteristics