Multi-factor Aging Of Transformer Insulation Paper And Its Vibration Evaluation Methods

Power transformers are important equipment in power systems,and their stable operation is critical to the safety and reliability of the power grid.The degradation of the electrical and mechanical properties of the insulating material will affect the reliable operation of the transformer and is considered as a key factor in assessing the remaining life of the transformer.In recent years,the state monitoring methods of power transformers based on vibration analysis have been extensively studied and many advances have been made.However,in the existing research results,there is a lack of discussion on the relationship between transformer insulation aging and its vibration characteristics.The research on the aging of insulation materials mostly focuses on the degradation process of mechanical properties or insulation performance with a single stress.There is a lack of research on the degradation of the mechanical properties of insulating materials under the combined action of thermal,electrical and mechanical loads.Therefore,it is necessary to study the degradation of mechanical properties of transformer insulation materials under multiple stresses and establish the relationship between insulation aging and transformer vibration characteristics.The degradation of mechanical properties caused by multi-factor aging of insulation materials was taken as the starting point in this paper.The relationship between the vibration characteristics of transformers was studied,and a vibration test system that can achieve relevant analysis functions was designed and developed.The main content of this paper is summarized as follows:Firstly,three insulation paper aging experiments including thermal aging,mechanical-electrical aging,and thermal-mechanical-electrical aging were designed and implemented.The tensile strength and stiffness were tested,and the evolution was analyzed.The strength decreases and the stiffness increases.Mechanical vibration and partial discharge will reduce the tensile strength and stiffness of the insulating paper.According to the micro-morphology of the insulation paper before and after aging,the above-mentioned phenomenon was reasonably explained.Using the molecular dynamics model to fit the above aging process,an empirical model of tensile strength and stiffness changes under the combined effects of heat,electricity,and machinery was obtained.Secondly,based on the aforementioned observations,the empirical model was incorporated to the vibration modeling of the transformer.Moreover,the relationship between insulation aging and transformer vibration characteristics was analyzed.The modal analysis method was used to study the vibration characteristics of the transformer,and the change rules of resonance frequency and FRF(Frequency Response Function)in the insulation aging process were obtained.Finally,based on the above research results,a vibration monitoring system for FRF analysis is designed and developed.The real-time acquisition,storage and display of vibration signals,and the spectrum analysis and FRF calculation of vibration signals were realized under the condition of detachment from the host computer,which provides a reference for the evaluation of the aging state of the transformer insulation.