The state of water in oil-impregnated paper insulation

Time domain reflectometry (TDR) between 1 MHz and 8 GHz was used to determine the state of water (bound or free) in oil-impregnated paper insulation. Bound water was found in paper impregnated with new oil, while a mixture of bound and free water appears to be present when the oil is oxidized and in unimpregnated paper. An explanation is proposed based on the more or less hydrophobic environment surrounding the cellulose matrix. In other words, the relative (hydrophilic to hydrophobic) character of cellulose, new oil, used oil, and air may explain the observed differences.<
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