Determination of Internal Moisture Diffusion Coefficient of Locally Damped Insulation Paper Based on Terahertz Spectroscopy

Localized dampness in oil-immersed transformers occurs from time to time, resulting in uneven distribution of moisture in the oil-paper insulation, which is a great threat to the safe and stable operation of the transformer, and it is of great significance to study the moisture migration characteristic in this case. It is found that the moisture in the locally damped oil-paper will migrate to the oil and the inside of the paper at the same time, which corresponds to two different moisture diffusion coefficients, the former is the diffusion coefficient to the oil ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${D_{oil}}$</tex> ) which is widely studied at present, and the latter is the diffusion coefficient to the inside of the paper ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${D_{{\text{(paper\ }}}}$</tex> ). In this paper, a new moisture detection method was proposed to determine the dynamic spatio-temporal distribution results of moisture in oil-paper insulation by terahertz scanning spectroscopy, and then <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${D_{{\text{(paper\ }}}}$</tex> was obtained by a new proposed algorithm. The results showed that there was still a positive exponential correlation between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${D_{{\text{(paper\ }}}}$</tex> and moisture concentration of the insulation paper.