Abstract The moisture content has a great influence on the electric insulation strength of oil‐pressboard. Therefore, it is very important to assess the moisture content in power transformers. There is lack of research about the effect of DC electric field on moisture migration. Here, the authors analyse the moisture migration characteristics of oil‐pressboard under DC electric field. The DC electric field has a greater influence on the moisture content in the oil. Compared with no DC electric field, the moisture content in oil is reduced by 22.91 mg/L at 50°C, while it is reduced by 17.63 mg/L at 70°C. Under the same moisture content in the oil, the moisture content in the pressboard which affected by the DC electric field is higher than the Oommen curve, the maximum difference is 0.88% at 50°C, and 0.05% at 70°C. This result can provide a reference for the revision of existing moisture assessment methods.
