Analyzing dynamic of moisture equilibrium in oil-paper insulation in power transformers for efficient drying

Moisture equilibrium in oil-paper insulation is dependent on temperature and the condition of power transformer. There exist balance charts for the percent of moisture in oil or in paper insulation at different temperatures in steady state but the dynamic of immigrating water from oil in to paper insulation and vice versa is very complex so an appropriate mathematical model has to be used to analyze the phenomena. In the other hand the dynamic of water exchange between oil and cellulose in different conditions is very important for optimum drying of aged power transformers particularly when drying performed on-site. In this contribution the equilibrium of moisture in oil-paper insulation based on temperature and transformer parameters is analyzed and the application of this analysis is illustrated for an efficient on-line drying system for power transformers.