| In recent years,China’s UHV DC transmission lines have increased a lot.As one of the core equipment of UHV DC transmission technology,converter transformers are related to the safety and stability of the entire power system.The insulation problem is the main cause of the fault of the converter transformer,during the operation of the converter transformer,the insulating material will be subjected to the combined effects of AC and DC composite electric field,high temperature,mechanical vibration,etc.for a long time.When the insulation deteriorates continuously,partial discharge and other phenomena may occur,which further deteriorate the insulation and ultimately endanger the safe and stable operation of converter transformer.Studying the aging mechanism of converter transformer oil-paper insulation is of great significance for understanding the insulation deterioration,assessing the insulation aging status and predicting the life of converter transformers.This paper firstly studies the effects of temperatures,mechanical vibrations,AC and DC electric fields on the key characteristic parameter of oil-paper insulation by test,and then systematically studies the the microscopic process of oil-paper insulation deterioration through molecular dynamics simulation.Finally,the connection between the macroscopic phenomenon and the microscopic mechanism of the oil-paper insulation’s deterioration is established.The innovative achievements obtained in this paper mainly include:①Single thermal,thermal-mechanical vibration combined,thermal-electric field combined aging test devices are designed in this paper;after the aging test,the characteristic parameters of the oil-paper insulation are measured according to the relevant standards;and then by analyzing the data,the degree of influence of each factor on the deterioration of the oil-paper insulation of the converter transformer is described.②The insulating paper molecular model and the cellulose chain model are built;the influence of temperature on the kinetic energy,potential energy,non-bonding energy and hydrogen bonding of the cellulose chain are analyzed by simulation;then the influence of electric field on the main chemical bond length of cellobiose molecules is studied,and the microscopic explanation about the acceleration effect of electric field on the deterioration of insulating paper is made;by molecular dynamics simulation on the insulating paper model,the content changes of the main products are statistically analyzed,and the generation path of the main products was obtained,which establishes a connection with the test measurement results.③This paper researches the main components of naphthenic insulating oil and establishes the model of insulating oil and oil-paper composite system;then the diffusion capacity of H2O,C2H4 and CO2 molecules in insulating oil is analyzed and compared with their diffusion in insulating paper;by molecular dynamics simulation on the insulating oil and oil-paper composite model,the mechanism of the pyrolysis of insulating paper on the promotion of insulating oil is studied. |
