Acidity in the insulation paper is an important characteristic to reflect and influence the aging degree of the paper

but there is yet no standardized method to determine it. Consequently

we established a test method of acidity in the transformer insulation paper. Firstly

carboxylic acid of small molecule in the paper was extracted by pure water so that solution containing acids of the paper was obtained. By titration to the acidic solution with isopropyl alcohol solution of KOH and deciding the end point with BTB

the acidity of the acidic solution was measured and the acidity of the paper was calculated in turn. The most appropriate temperature（25 ℃） and extraction time（6 h） condition for the measurement were ensured based on contrast experiments. By monitoring the acidity and water moisture in oil-paper insulation

the new method was found to well indicate the physical truth; acidity in paper fluctuated with time just like the water moisture in paper; the acidity in paper and oil had little relationship with each other.