Water in Oil-Filled, High-Voltage Equipment, Part I: States, Solubility, and Equilibrium in Insulating Materials

The major part of the water in paper insulation influences its electric characteristics, chemical stability, and mechanical durability. The analysis of moisture in oil, with the subsequent estimation of moisture in solid insulation, is therefore of great interest in assessing the condition of electric equipment in service. In the first part of a two-part article, we examine the current state of knowledge on the effect of water on paper and liquid insulating materials. The second part describes the influence of water on the electrical characteristics of the oil/paper insulating materials, gives a critical review of up-to-date water quantification methods, and proposes some analytical expressions that can help electrical engineers monitor and/or diagnose oil-filled, high- voltage equipment.