Study On Electrochemical Corrosion Of Ultra/Extra High Voltage Dc Insulator Fittings And Its Preventive Measures

China has a vast territory,complex terrain and diverse climatic conditions,which is likely to cause electrochemical corrosion of insulators in ultra-high voltage direct current transmission lines.Corrosion of the DC insulator does not only reduce the mechanical bearing capacity of the insulator,at the same time,the corrosion product adheres to the surface of the insulator skirt,which greatly reduces the flashover voltage of the insulator string,posing a serious threat to the safe and stable operation of the power system.In this paper,the potential distribution and leakage current distribution of the insulator string are simulated,and the resistance circuit of the insulator string is derived.The electrical corrosion characteristics of the metal electrode and the insulator metal fittings under DC voltage are studied experimentally.Finally,the research gives measure that insulators are protected against corrosion.The unevenness of the corrosion of the insulator metal is related to the distribution of the electric field,leakage current and space resistance.In this paper,the threedimensional finite element model of the insulator string is established.The potential distribution and leakage current distribution of the insulator string are simulated and the space resistance circuit of the insulator string is derived.The simulation results show that there are two strong electric field regions in the suspension insulator,they are the junctions between the gap between the insulator and the iron cap,the steel foot and the cement adhesive.The DC insulator string's potential distribution is a dynamic equilibrium state of two modes,capacitive partial pressure and resistance partial pressure.The leakage currents flowing through the insulators are not equal.The main reason is that there is space resistance between the insulators' fittings.These space resistance provide multiple paths for leakage current.Subsequently,various shapes of electrodes were fabricated using different materials of metal,and the electrodes were subjected to DC accelerated corrosion test to investigate the effect of DC electric field on the corrosion of metal electrodes.At the same time,the insulator was subjected to a DC accelerated corrosion test to study the corrosion characteristics of the insulator under the action of DC voltage.The test results show that the stronger the electric field strength is,the faster the corrosion rate of the metal electrode is under the action of DC voltage.The corrosion speed and corrosion mode of the protection zinc ring are different at different inclination angles of the insulator.The main reason is that the flow path of water and contamination accumulation of the insulator surface are different at different inclination angles.Insulator metal fittings corrosion can be divided into two stages.In the first stage,the corrosion product does not touch the fitting,and the leakage current on the surface of the insulator mainly flows through the water flow path.In the second stage,the corrosion product touches the fitting,and the leakage current on the surface of the insulator is mainly affected by the corrosion product.The second stage of the corrosion process is a positive feedback process of “corrosion product generation—increased leakage current—corrosion is intensified—increased corrosion product”,and the effect on corrosion of the metal fitting is significantly greater than that in the first stage.Finally,according to the environmental conditions required for the corrosion of insulators,the corrosion prevention measure is proposed,and the feasibility of the prevention measure is verified by experiments.The results show that spraying PRTV on the surface of the insulator iron cap will reduce the electric field at the insulator iron cap gap but will not cause distortion of the electric field on the insulator surface.After the insulator cap is sprayed with the PRTV,the leakage current density on the iron cap is reduced,and the degree of reduction is related to the height of the PRTV coating.The uniform and dense PRTV coating adheres well to the surface of the insulator,and can separate the insulator from the air and moisture,which is beneficial to prevent corrosion of the insulators' metal fittings.