Study On Moisture Transfer Between Transformer Oil And Paper Based On Molecular Dynamics

Moisture is an important factor affecting the insulation performance of oil-paper.Its distribution inside the transformer is affected by temperature and electric field.It will migrate between oil and paper during the temperature change process.During the actual operation of the transformer,due to large fluctuations in load,there may be a rapid warming operation.The moisture in the insulating paperboard will migrate to the oil.Since the saturated water content in the oil is only one part per million,the water may accumulate at the oil-paper interface during the migration process to form a local high water partition.As a result,a malignant transformer accident such as creeping of the insulating cardboard is caused However;limited by the technical means such as macro sampling and measurement,it is impossible to accurately measure the migration and diffusion process of moisture at the interface of the oil-paper.The emergence of molecular simulation technology provides a means to study the diffusion behavior of water molecules at the oil-paper interface.Based on the molecular dynamics method,a molecular model of 105 atomic oil-paper composite media which is the largest model in the field of electrical engineering was established on a self-built server cluster and the migration process of water molecules in oil-paper insulation media during 20?-80? heating process was simulated.The feature states such as the aggregation state of water molecules,the number of hydrogen bonds,hydrogen bonding force,motion trajectory,diffusion coefficient and initial moisture content were extracted-and the microscopic mechanism of water molecule migration was revealed from the molecular level.Moreover,based on the microscopic molecular model,the migration process of water molecules under the coupling condition of electric field and temperature field was simulated,and the similarities and differences of water molecule migration under the condition of electric field were compared.What's more,based on the mesoscopic dynamics method,a mesoscale molecular model of oil-paper insulation medium was established and its equivalence with microscopic molecular model was verified.The results show that:the water molecules in the insulating paperboard will diffuse into the mineral oil during the heating process in the absence of an applied electric field.When the moisture in the insulating paperboard exceeds S%,the rapid temperature rise will cause the water molecules to move to the oil-paper interface.And the hydrogen bonding force is integrated into the water molecule cluster to form a partial liquid water partition.When the moisture content exceeds 7%,a large liquid water partition is formed,which seriously jeopardizes the operational safety of the transformer.After the electric field is applied,when the moisture content of the insulating paperboard exceeds 4%,the rapid temperature rise will cause water molecules to aggregate into water clusters at the oil-paper interface to form local liquid water.When the moisture content exceeds 5%,a liquid water partition will be formed.Moreover,the polarization of the electric field enhances the hydrogen bonding force between water molecules and increases the probability of occurrence of high water partitions.The free volume and diffusion coefficient of water molecules are reduced,and the diffusion coefficient is anisotropic.In addition,the accuracy of the mesoscopic model of the oil-paper composite medium was verified by collecting the diffusion coefficient of water molecules.The spatial scale was expanded by 100 times compared with the microscopic model,and the operating efficiency was improved by nearly 10 times.