Temperature-dependent contamination distribution between oil, paper and pressboard

A fully enclosed oil circulation rig has been made for studying the temperature-dependent equilibrium distribution of contaminants between oil-impregnated cellulose materials and oil. This is relevant for the distribution of contaminants in the solid insulation in power transformers. Used with clean, new material the rig gave humidity equilibrium results reasonably close to results found in literature. With service-aged pressboard the humidity results departed from the values from literature for clean, new material. The results had some inner consistency indicating that they were reasonably trustworthy despite some uncertainty because of long diffusion times in pressboard and some measurement uncertainty. It was also attempted to look into temperature-dependent equilibrium distribution of acids, but the variation with temperature was too small compared to the measurement uncertainty. It was also found that the rig is suitable for studying the temperature-dependent humidity saturation in otherwise contaminated oil at high temperatures.