Flow electrification in power transformers: study of a potential remedy

Understanding the exact nature of the phenomena at the origin of the electrical charging tendency of transformer pressboards submitted to oil circulation in high power transformers is still a challenging problem. Former studies demonstrated that the flow electrification phenomenon depends a lot on the functional groups of the pressboard surface, and especially carboxyl groups. In this study, the action of several additives has been tested. Three experimental devices available in Poitiers laboratory (conductivity cell, flow loop and ECT test devices) have been used to investigate the effect of the additives on the charge generation, accumulation and leakage currents. Moreover, experiments with demineralised pulps treated by carboxyl complexing agents such as methylene blue have confirmed the important role of ionizable groups in papers. It has appeared that some additives can reduce the electrification phenomenon. In addition, as these results remind of some ionic chromatography (IC) aspects, the related theory can be attempted to explain the chemical process, which takes place between the oil and the pressboard.