Effect of Temperature on Moisture Adsorption and Desorption in Cellulose Insulation

The rise and fall of the internal temperature of power transformer will cause the moisture to change its distribution and aggregation position, and the local high moisture content will seriously affect the electrical strength of oil-paper insulation. Therefore, it is necessary to study the adsorption and desorption of moisture in cellulose insulation at different temperatures. In this paper, three oil-cellulose mixed systems (OCS) of 105 atoms with different moisture contents were established by molecular dynamics method, and temperature rise and temperature drop simulations were conducted respectively. The changes of the water molecule number (NW) in the interface domain and oil domain were obtained. By analyzing the solvent accessible surface area (SASA) and the microscopic scanning electron microscope (SEM) images of cellulose insulation, the effect of temperature changes and the deterioration of cellulose molecules on the moisture adsorption and desorption in cellulose insulation were studied. The results show that after the high-temperature system is reversely cooled, water molecules in the oil domain will migrate rapidly to the cellulose domain, while the irreversible deterioration of cellulose after high temperature leads to the weakening of its adsorption capacity. As a result, a large amount of water is retained at the interface. For the simulation of temperature rise, the higher the temperature is, the more water molecules accumulate in the oil domain and interface domain, and the stronger the desorption effect of cellulose on moisture. Notably, NW in the interface domain is not a simple increment trend, but an oscillatory increase and decrease trend that decreases first and then increases. The higher the temperature is, the more obvious the trend is. The research results have important theoretical value for the real-time monitoring of moisture in oil-immersed power equipment and the evaluation of its insulation performance