Evaluation Method of Oil-paper Insulation Damp State Based on Response Current Value Change

Insulation moisture will seriously affect the safety of equipment operation. The response current characteristics of oil-paper insulation with various degrees of moisture from 50 Hz to 0.01 Hz were tested in this paper, and the $f-I^{\star}$ curves were proposed to uniformly characterize the test results of different objects. The test results indicate that the $f-I^{\star}$ curve of dry oil-paper insulation is a straight line, and the increase of moisture content will significantly change its shape in low frequency band and become a concave curve. The insulation structure will not affect the $f-I^{\star}$ curve, and there is an obvious correlation between $I_{50}^{\star}$ in the curve and specific content of moisture. $I_{50}^{\star}$ is proposed as a characteristic parameter that can effectively reflect the water content of oil-paper insulation.