Quantitative Evaluation Of Micro Water Content In Solid Insulation Of Transformer Based On Frequency Domain Dielectric Modulus

Oil-immersed power transformer is one of the most important equipment in power system,which is responsible for power transmission and transformation.The insulation state of transformer determines its service life,and the moisture content is one of the important factors affecting the insulation state of oil paper.The moisture content evaluation of solid insulation materials in oil paper insulation system of transformer based on frequency dielectric spectrum technology has always been the focus of researchers.However,in the process of dielectric response measurement in frequency domain,the electrode polarization effect and conductivity effect will make the relaxation information fuzzy,which often leads to misjudgment.To solve this problem,it is shown that the frequency dielectric modulus spectroscopy M*(ω)can effectively study the relaxation behavior and highlight the details of polarization response.At present,there are few reports on the research methods of dielectric properties of solid insulating materials and quantitative evaluation of moisture content based on frequency domain dielectric modulus.Therefore,this paper attempts to propose a method to extract the characteristic parameters based on the dielectric modulus for the quantitative evaluation of the moisture content of solid insulation materials of transformers.In order to avoid the influence of aging on the moisture content evaluation of insulating board,this paper first divides the aging into four degrees,using accelerated thermal aging and moisture absorption test to prepare 16 groups of oil-immersed pressboard samples,and carries out frequency-domain dielectric response test and physical-chemical parameter analysis.Then,by analyzing the dielectric modulus spectroscopy in frequency domain and extracting the integral IV of the real part,the peak V_pof the imaginary part,the characteristic frequency f_pand the relaxation time constantτ_Mof the real part of the dielectric modulus from the samples of each aging degree as the characteristic parameters,the change rule of the moisture content mc%on the above parameters is further studied.The quantitative relationship between mc%of water content and each characteristic parameter is established by using fitting analysis.Finally,the feasibility of the proposed method is verified by the quantitative evaluation of water content of the samples to be tested in the laboratory and the field transformer combined with XY model.The results show that the water content evaluation results of the samples to be tested in the laboratory and the field transformer are basically consistent with the test results.It is concluded that the above characteristic parameters can be used as a potential tool to quantitatively evaluate the moisture content of solid insulation in oil-paper insulation system of transformer.