Study On Ultrasonic Detection Method For Partial Discharge Of Power Transformer

Along with the construction and development of China's strong and smart grid,the scale of the power system is expanding especially the construction of UHV AC / DC transmission in the country.The on-line detection technology of transformer partial discharge insulation has attracted the attention of the electric power industry.At present,the evaluation method of insulation state of power transformer is mainly based on the evaluation of some characteristic parameters of the insulation medium in the deterioration process including the tangent of dielectric loss angle,leakage pulse current,partial discharge,etc.The partial discharge is one of those that can reflect the local state of the power transformer which has an irreplaceable role in the insulation on-line detection.Therefore,it is of great academic significance and application value to study the partial discharge detection method of power transformer.The research contents of this paper are as follows:(1)In this thesis,the process of partial discharge is discussed based on the theory of gas discharge,then the mechanism of partial discharge ultrasonic wave is analyzed,and taking the bubble discharge in transformer as an example.The stress process of bubble breakdown is analyzed.Based on the principle of electric force analogy,a mechanical equivalent circuit model of ultrasonic generated by partial discharge is established.On the basis of the above research,the laboratory test and simulation analysis of the propagation of ultrasonic signal in the simulation of the transformer oil tank are carried out.The experimental research mainly includes: the propagation velocity of ultrasonic wave in the transformer oil and oil immersed insulation paper,and the analysis of the amplitude attenuation of the ultrasonic signal passing through the insulation medium.(2)On the issue of the partial discharge signal of transformer is disturbed by the complex operating environment,a combined detection method for suppressing the interference in layers is proposed in this thesis.Basing on the analysis of the propagation characteristics and the characteristics of the frequency distribution of the PD signal and the disturbance signal,a layered interference suppression model based on band-pass filter and wavelet analysis is proposed.The effectiveness and feasibility of the proposed model has been proven according to the simulation results.(3)Based on the analysis and comparison of partial discharge location method in this thesis,a genetic algorithm with global search is used,and the results are compared with the least square method.The results show that the genetic algorithm can solve the problem of least square method in the location of the edge region.Thus,the positioning effect is ideal with use value.