| This project is a sub topic of the National Natural Science Foundation of China(No.61174117)?Research on diagnosis of Oil-Paper Insulation Condition Based on Recovery Voltage Response and Circuit Analytical Method?.Oil-impregnated transformer is one of the most important equipment of electric power transmission and transformation in power systems.The transformer accidents will not only cause enormous economic loss,but also threaten the public security and result in serious social problems.Recently,studies show that the transformer failure caused by insulation aging accounts for an important part in the transformer accidents.Therefore,it is important to make accurate assessments on the ageing condition of the insulation of the transformer to guarantee the safe operation of power networks and improve the efficiency of maintenance and repair works.In this thesis,the return voltage method(RVM)is introduced to assess the condition of oil-paper insulation system in oil-immersed power transformers.We first extract some dielectric relaxation response parameters(RRP)from the return voltage curves,and construct an equivalent relaxation response circuit concerning the oil-paper insulation.Subsequently,we study the correlativity between the condition of oil-paper insulation and extracted RRP,and exploringly present a concept of multi-parameter to quantify and evaluate the aging degree of transformer insulation.Finally,we predict the lifetime of oil-paper by combining with multi-parameter and the running environment.The main research work is as follows:(1)By using the RVM,we extract the RRP of oil-paper insulation and construct the function between the RRP and Debye equivalent circuit.Subsequently,we determine the topology of the equivalent circuit and obtain an accurate identification of the parameters of equivalent circuit based on the constructed function.Besides,we further study a multi-interface relaxation polarization circuit model,and discuss the relationship between multi-interface relaxation polarization circuit model and Debye equivalent circuit model.(2)According to the correlativity between the condition of oil-paper insulation and extracted RRP,we obtain characteristic to quantify and evaluate the aging degree of transformer insulation.The characteristic include relaxation numbers,time constant,linear parameters in the relaxation process,and the ratio of relative relaxation charge and oil-paper aging time.Furthermore,we deeply analyze the rule of the oil-paper insulation status and the relaxation response characteristic,and discuss the mechanism and correlativity behind the analyzed rule.(3)The condition of oil-paper insulation will be affected by various factors,it is hard to make accurate assessments on the ageing condition of oil-paper insulation via any single characteristic.In this thesis,by combining with the grey target theory and some special characteristics concerning the ageing condition of oil-paper insulation,we prose a novel method which can improve the traditional grey target method and give quantify and evaluate the aging degree of transformer insulation.In addition,the feasibility of the novel method is validated by an example.(4)Based on the analyzing the relationship between RRP and water content of insulation paper,we further analyses the mechanism of the effects between water content and the related parameters.The equation of multiple nonlinear regression are established to quantificationally evaluate the water content.On the premise of making comprehensive consideration for the water and running environment,we put forward scheme of predict the insulation life of oil paper insulation based on RRP,and the feasibility and correctness of the scheme are validated by an example.The above researches have important practical significance and value of application on grasping the status of oilpaper insulation timely and accurately,ensuring the safely and steady operation of power network,heightening the operational reliability of equipment,and direct the power equipment. |
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