| With the improvement of the voltage level of the Direct-Current transmission line,the corrosion problem of insulator fittings has become increasingly prominent.The corrosion of metal fittings will reduce the mechanical properties of the insulator and seriously threaten the safe operation of the power system.The current mainstream view is that electrolytic corrosion caused by leakage current is the main reason for the corrosion of metal fittings,and based on this,the researches on the corrosion amount,test methods and anti-corrosion measures of metal fittings are carried out.However,new research has found that the corrosion of metal fittings can still be caused under the condition that only the electric field acts without the formation of a loop,and only the electrolytic corrosion caused by leakage current as the cause of corrosion can no longer meet the anti-corrosion requirements of metal fittings.The corrosion mechanism is still unclear.In addition,it is difficult to directly measure the microscopic process of corrosion of metal fittings under DC electric field,but the process is accompanied by changes in macroscopic quantities caused by electrochemical parameters.Therefore,this paper mainly uses the method of simulation combined with experiment to study the microscopic mechanism of metal corrosion,explores the law of ion migration on the electrode surface,and provides a theoretical basis for anti-corrosion measures of metal tools.Firstly,this paper establishes a simulation model of suspended insulator strings,studies the potential distribution law of positive and negative polarity insulator strings,explores the influence law of the structure of the High-Voltage equalizing ring,the DC voltage level and the number of insulators in each string on the distribution of the potential of the fittings.The potential bearing rate of the piece insulator fittings changes,and the range of the field strength of the fittings under the ±800k V voltage level is obtained.In addition,according to the simulation data,the influence of the DC voltage level on the leakage current of the insulator is summarized.And it is found that the surface potential distribution of the fittings and the leakage current distribution of the insulator are always non-uniform.Secondly,a simplified model of electrochemical corrosion of metal fittings is established in this paper,and the boundary conditions are set according to the range of electric field strength of metal fittings obtained above.The electrode current density vector,electrode current and overpotential distribution is used as characterization quantities,and the presence or absence of an applied DC electric field is studied respectively.The change of corrosion rate of metal fittings was compared,and the corrosion difference of positive and negative electric field on the iron electrode and zinc electrode was compared.The research shows that,according to the changes of metal electrodes current,overpotential and polarization region,the participation process of external DC electric field on metal corrosion can be reflected from the microscopic point of view.Finally,this paper carried out an experimental study on the influence of DC electric field on the corrosion of metal fittings,and conducted exploratory experiments such as dissolved oxygen experiment,complementary color laser experiment,electrical aging ceramic plate experiment,polarization potential experiment,and bar-plate pressurization experiment.The feasibility of the results is determined,and the rod-plate pressurization experiment with depolarization potential as the characterization quantity is determined as the experimental scheme.A rod-plate pressurization experimental platform was built to study the influence of diverse applied voltage time on the depolarization curve of the metal electrode,and a possible explanation was proposed from the perspective of the circuit model,that is,under the action of a DC electric field,the ions in the solution migrate from the whole the formation of an induced dipole moment transitions to localized ion migration to the electrode surface.The feasibility of this explanation is verified by studying the influence of solution ion type,solution ion concentration,and electrode surface state on the measurement results.At the same time,an isometric simulation model was established to study the characteristics of particle migration under the electric field,and to verify the experimental results.To sum up,this paper starts with the simulation study of the surface potential distribution law of the hanging insulator string fittings,and studies the electrode current and overpotential distribution law of the metal electrode under the condition of only applying a DC electric field without forming a loop,and proposes a depolarization method.The chemical potential detection method is used to study the ion migration process of metal electrodes under an electric field,and to explain the microscopic mechanism of metal corrosion. |
