Experimental evaluation of water content determination in transformer oil by moisture sensor

Paper presents experimental research on temperature dependency of water solubility in mineral transformer oils. Moisture sensor measurements and absolute water content determination by Karl Fisher titration method were performed under controlled laboratory conditions to investigate solubility models of different types and conditions of mineral transformer oils. Results of experiments demonstrate that preset moisture solubility model of the moisture sensor affects accuracy of water content determination. Test setup and optimised procedure for verification and calibration of the moisture sensor with oil-specific solubility parameters is described, tested and evaluated. This allows higher accuracy of on-line water content monitoring in operating transformers under changing temperature conditions.