Frequency Domain Spectroscopy Characteristics of Transformer Oil-Paper Insulation Under Wide Temperature Range

As the core component in oil-immersed power transformers, oil-paper insulation exhibit dielectric properties heavily influenced by temperature-humidity coupling. This study systematically investigates the dielectric loss factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(tan \delta)$</tex> evolution across a broad temperature range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(-20-70^{\circ} \mathrm{C}\right)$</tex> using frequency domain spectroscopy (FDS). Dry-state <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(&lt;0.5 \%$</tex> water content) and damp-state (4.2% water content) oil-paper insulation samples were prepared for analysis. Experimental results demonstrate that within the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10 \text{mHz}-1 \text{kHz}$</tex> frequency band, tand for both dry and damp insulation rises exponentially with temperature. Notably, damp samples exhibit <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{tan} \boldsymbol{\delta}$</tex> increases 2-3 orders of magnitude greater than dry samples in low-frequency regions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(&lt;0.1 ~\text{Hz})$</tex>, highlighting moisture's role in amplifying dielectric loss through intensified interfacial polarization and ionic conductivity. These findings establish a dielectric response database under temperature-wetness coupling, supporting transformer insulation diagnostics across diverse operating conditions.