Study On Condition Diagnosis Of Transformer Based On Time And Frequency Analysis Of Relaxation Current

Transformer is one of the most critical aspect of power system.Potential faults could be detected and repaired via condition diagnosis,so as to ensure the safe operation of power grid and improve its economic efficiency.Therefore,to establish a complete on-site diagnosis and assessment system for transformer is currently one of the most important and valuable works in power industry.Several phenomenon could be found in analyzing broadband dielectric spectroscopy,dissolved gas analysis,as well as breakdown strength of electrically aged oil-paper samples.Firstly,the hydrocarbon gas content in the oil samples increases with aging time,which can be deduced that the aging occurs mainly in the pressboard.Secondly,the increment of conductivity and dielectric loss indicates the appearance of impurities originating from the aging byproducts of the pressboard.Thirdly,the dispersion of the real part of the relative dielectric constant and the overall rise of the imaginary part implies an increase of interfacial polarization extend inside the sample due to the appearance of byproducts.Moreover the increment of parameters in each experiment mentioned above strongly implies the strong polarity of byproducts.Finally,the results of characteristic breakdown deduced from Weibull distribution,as well as the AC breakdown strength indicates that the withstanding voltage and the remaining life of oil-paper samples declines significantly with aging time.What's more,the shape parameter ? and variance of breakdown strength reveals that the divergence of breakdown strength decreases with aging time.According to the relaxation currents of samples prepared with three different aging types,it was found that all the currents shift upwards and the amplitude gradually increases with aging time,and the more severely aged the sample,the greater the currents were.In addition,based on the measured currents,parameters are extracted from a modified Debye model,as well as trap density and the charge amount calculated from the polarization and depolarization currents.It was found that three assessment parameters showed the consistent trends with the aging time,which indicates the feasibility of assessing aging degree for oil-paper insulations.At last,the remaining life of a transformer was studied through an on-site diagnosis technology based on polarization and depolarization current measuring in time domain.All the data obtained from each of three transformers shows a consistence to the life information acquired in advance.What's more,a rapid on-site assessing technology were developed for oil-paper insulating transformer.