Effect of Electric Field on the Moisture Equilibrium of Oil-Paper

An accurate assessment of moisture content is important for the electrical insulation strength and aging life of the solid insulation inside the transformer. However, there is still a major reliance on the Oommen curves to indirectly calculate the moisture in paper, which only takes into account the effect of temperature and not the effect of the electric field. Therefore, the experiment on the effect of direct current electric field (DCEF) on the moisture equilibrium characteristics of oil-paper is carried out in this work. Firstly, a tested platform with applied voltage and heating is constructed, then the moisture in oil and paper with different DCEF strengths under the same temperature is tested non-destructively and globally by using terahertz spectroscopy, and finally, the test results are compared with the Oommen curves for data comparison. The results show that when the paperboard samples with the same moisture content reach equilibrium, the applied DCEF is more moisture than that without DCEF, and the DCEF may inhibit moisture diffusion. Moreover, with the increase of the strength of DCEF, the more the average increment of the moisture. This study obtains the moisture equilibrium law of oil-paper under different DCEFs, which lays the foundation for correcting the Oommen curves and calculation equation.