Effect of direct current electric field on water diffusion

Moisture is a key factor affecting the electrical performance and material deterioration of power transformer oil-paper insulation. Therefore, it is of significant importance to study the diffusion law of moisture in oil-paper insulation to ensure the safe operation of transformers. However, the lack of suitable non-destructive testing means has led to few experimental studies on the diffusion law of electric field on moisture in insulating paper. For this purpose, utilizing the characteristics of non-destructive and full-range testing of terahertz spectroscopy, in this paper, an experimental study was carried out to investigate the effect of DC electric field on the diffusion of moisture in oil-immersed insulating cardboard. The results show that the electric field will inhibit the diffusion of moisture in oil-paper insulation. And the inhibition effect increases with the increase of electric field strength. The calculated diffusion coefficients tend to decrease with the increase of electric field, from 0 kV/mm to 1.2 kV/mm, the diffusion coefficients decrease about 6 times. This study is of significance for the subsequent study of moisture distribution in the presence of multi-physical fields and the formation and development of latent defects in transformer insulation.