Study On Mechanical-thermal Aging Characteristics And Lifetime Evaluation Of Insulating Paper

As the key equipment of power system,the aging of oil-paper insulation in power transformer has been the focus of research.In the actual operation of transformer,the winding vibrates under the joint action of load current and leakage magnetic field,especially in the converter transformer,the winding vibration will be more intense,the insulating paper wrapped on the winding will bear higher mechanical stress,and the existence of mechanical stress will affect the aging process of the insulating paper.In order to further improve the operation safety of transformer,it is necessary to study the aging rule of insulating paper under the combined action of mechanical and thermal stress.This paper takes the oil-paper insulation as the research object,carries out the mechanical-thermal accelerated aging test in the laboratory,studies the change rule of the related characteristic quantity of the insulating paper in the aging process,and proposes the life evaluation model of the insulating paper based on the time-stress-temperature superposition method.The results and conclusions are as follows:(1)This paper introduces the vibration mechanism of transformer windings,and constructs the paper-winded winding model in multi-physics field simulation software.The stress of insulating paper is analyzed by simulation,and the range of tensile stress intensity in the mechanical-thermal combined aging is determined.Finally,the mechanical-thermal combined aging platform was designed and manufactured.(2)The test results of polymerization degree,tensile strength,infrared spectrum and scanning electron microscope of insulating paper under different mechanical-thermal aging forms are obtained.The results show that the performance of the insulating paper under mechanical-thermal aging is more obvious than that of thermal aging,and the aging degree of the insulating paper deepens as the stress intensity increases.(3)The mechanical-thermal combined aging of insulating paper includes both physical changes of cellulose deformation and internal force attenuation,as well as free chain chemical reactions.These reactions promote each other,resulting in a higher rate of mechanical-thermal combined aging than a single thermal aging rate.According to the polymerization degree fitting results,the mechanical-thermal combined aging rates at 1 MPa,1.5 MPa,and 2 MPa are 1.20 times,1.36 times,and 1.69 times the single thermal aging rate under 130℃,respectively.(4)The change law of polymerization degree under mechanical-thermal aging satisfies the kinetic model in terms of the percentage DP loss,and mechanical-thermal aging can be regarded as single thermal aging with lower degradation activation energy.The activation energy reduced by the tensile stress at 2MPa is 2476 J / mol.The lifetime evaluation model of insulating paper under different mechanical tensile strengths and temperature can be obtained by time-stress-temperature superposition method,which provides reference for the prediction of insulating paper life.