Moisture solubility for differently conditioned transformer oils

It is important to monitor the moisture content of transformer oil in a transformer. One parameter of particular interest is the moisture solubility of transformer oil. It has been reported that transformer oils under different conditions have different solubility. Measurements of solubility for four different types of conditioned oil are presented in this paper: fresh Shell Diala AX oil, lab-aged Shell Diala A oil, Texas Utility used transformer oil, and Ramapo Substation used transformer oil. To avoid the difficulty of achieving full saturation, this paper proposes an alternative method of measuring the moisture solubility in transformer oil using a relative humidity sensor. It utilizes the linearity between the relative humidity of the oil and the moisture content of the oil, to measure the solubility indirectly. The measured results of fresh oil, lab-aged oil, and the Texas Utility oil are very close, and only Ramapo oil shows different sensor response characteristics and solubility.