Research On Aging Condition Assessment Of Oil-paper Insulation Transformer Based On Dielectric Relaxation Response

Oil-paper insulation electrical equipment such as transformer,mutual inductor,reactor,are basic components of the electrical system,their safety relates to stability of power system equipment.Insulation aging is the usual causes of oil-paper insulation electrical equipment breakdown.So it has important practical significance to improve the operational reliability of oil-paper equipment by detection method of aging condition.The time domain dielectric spectroscopy is commonly used to assess the state of aging oil-paper insulation.It carries more information and it is a fast and effective diagnosis method.This study is supported by the Project of Chinese National Science Foundation:the aging diagnosis method of oil-paper insulation based on circuit analysis and recovery voltage response(No.61174117).Making oil-paper insulation of electrical equipment as the research object,and according to time domain dielectric spectroscopy measurements,establishing mathematical model of media response and equivalent circuit model which can reflect the real dielectric relaxation response of oil-paper insulation so as to further analyze the relationship between the time domain dielectirc response characteristics and aging condition of oil-paper insulation.The research will provide a new idea for aging condition of oil-paper insulation.Main contributions of this thesis are listed as following:(1)Based on the theory of time domain dielectric response and the characteristics of oil-paper dielectric relaxation response,the time-domain response test methods and the principles and characteristics of extended Debye equivalent circuit model are introduced;According to build an equivalent circuit model by simulink platform,the variation of time domain dielectirc response characteristics is researched to determine the optimal experimental parameters by changing the test conditions.It laid a good experimental foundation for aging condition evaluation of oil-paper insulation using time domain dielectric response method.(2)The atypical linear of microscopic dynamics is used to improved atypical linear dielectric response function in order to accurately reflect the medium depolarization process.The method of second time-differential is firstly proposed to decomposition of different relaxation processes.This method not only determine branches polarization number accurately,but also ensure the parameter identification uniquely.Finally,analysis the internal relations between the polarization branches number,atypical linear and insulating oil and paper,which provide new ideas to locate aging insulating oil and paper.(3)Aiming at traditional method of parameter identification for relaxation response equivalent circuit,which can not eliminate fluctuations of charging voltage and measurement error,combined with actual datas,the interval-adaptive particle swarm optimization(I-APSO)was introduced to identify the parameters of oil-paper insulation.The algorithm not only reduces the actual error making the result more precise,but also locates the optimal solution areas of the parameters effectively.The result shows that depolarizing current curve by I-APSO can be matched better with test curve comparing with conventional method,which reflects the dielectric process of oil-paper insulation system more truly and effectively.(4)Two new parameters called the half-peak time and relaxation energy which can be used to diagnose the aging stages of oil-paper insulation are firstly proposed.The half-peak time is able to reflect the polarization rate of insulation condition,which is highly related to the aging stages.Relaxation energy is able to reflect the process of electric energy accumulation and release in relaxation mechanism of oil-paper insulation adequately.The relationship between time domain dielectirc response characteristics and oil-paper insulation aging is researched to explore the relationship between the compositions of oil-paper insulation and the time domain dielectric spectroscopy.