Impact of Moisture on Space Charge Characteristics of Multilayer of Natural Ester Oil-Impregnated Paper

This study explores the influence of moisture on the space charge properties of multilayer natural ester oil-impregnated paper. Natural ester oils, being polar, extract moisture from kraft paper, while the hydrophobic characteristics of mineral oil keep moisture in kraft paper. Under varying moisture conditions, natural ester oil-impregnated paper consistently shows higher charge accumulation than mineral oil-impregnated paper. Despite this, natural ester oil-impregnated paper demonstrates superior dc dielectric breakdown strength, attributed to its polar characteristics dispersing electrical stress more uniformly. The findings suggest that in highly humid environments, natural ester oil can be more advantageous than mineral oil for high-voltage direct current (HVdc) transformers.