Impact of Temperature on Dielectric Behavior of Oilimpregnated Insulation Pressboard

Oil-paper insulation systems are widely employed in converter transformers due to their excellent dielectric performance. However, the complex operating conditions of converter transformers result in a gradient temperature distribution within the oil-paper insulation materials, which significantly affects the dielectric characteristics of insulation pressboards. This paper investigates the dielectric properties of four commercially available insulation pressboards under temperatures ranging from 40° C to 100° C. Key parameters, including volume resistivity, dielectric constant, dielectric loss, and AC breakdown strength of oil-impregnated pressboards, were systematically measured. Experimental results demonstrate that temperature exerts a pronounced influence on the dielectric performance of oil-impregnated pressboards. As the temperature increases from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$40{ }^{\circ} \mathrm{C}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100{ }^{\circ} \mathrm{C}$</tex>, the volume resistivity of oilimpregnated pressboards decreased by two orders of magnitude, while the relative dielectric constant increased by approximately 15%. Additionally, the dielectric loss exhibited a gradual rise, and the AC breakdown strength declined by 10% due to elevated temperatures.