In order to accurately assess the moisture content in oil-paper insulation and study the effect of small molecule acid on the moisture evaluation of oil-paper insulation

the oil-impregnated paper samples with different moisture and formic acid content are prepared in this paper

and FDS test is carried out on it by using frequency domain dielectric spectroscopy

then on the basis of the spectroscopy a characteristic parameter of the moisture content of oilpaper insulation in different acidic environment is proposed.The research results show that the moisture will affect the distribution of small molecules acid in oil-paper insulation and then with the increase of moisture in paper and formic acid in oil

the tanδ spectroscopy from 10-3 to101 of oil-impregnated paper samples is significantly increased.Compared to the environment with no acid

the increase of formic acid makes the tanδ spectroscopy of oil-impregnated paper samples in the same moisture content a increase in varying degrees

so the influence of small molecule acid can’t be ignored in the actual measurement of moisture content of oil-paper insulation.The Stanδ of oil-impregnated paper samples

proposed in acidic environment

have a good exponential relationship with moisture content in different acidic environment and show a certain law with moisture with the change of acid content

so it can be used as the characteristic parameters of the moisture of oil-paper insulation in different acidic environment.