| Isolation switch is the most widely used high-voltage switchgear in transformer substation.However,due to the long-term outdoor service,its core component,contact finger is subject to erosion under atmosphere and various specific service conditions,resulting in frequent thermal defects.Unlike general corrosion,the contact finger is also subject to corrosion with the electric current.In order to improve its conductivity and corrosion resistance,the contact finger is usually coated by silver.However,due to the frequent on/off operations,the silver plating layer is easy to wear and peel off.Once the substrate of copper exposure occurs,the copper as cathode will be rapidly corroded and lose its excellent conductivity,threatening the safety and stability of power grid operations.In this paper,based on the application requirements,the corrosion behavior of the copper with electric current is studied,and Ag-graphene composite coating is prepared to improve the corrosion resistance and wear resistance of contact materials.The main research contents and results are as follows.Firstly,the corrosion behavior of the copper as the matrix materials of switch contact under electric current is studied by a self-made corrosion testing device.The results show that the corrosion weight loss of copper increases with corrosion time.The corrosion rate of copper increases first and then decreases.The higher the loading current is,the faster the corrosion rate is.The corrosion products produced without current have a certain protective effect on the Cu substrate,while the corrosion products produced with current have a weak protective effect on the substrate.The effect of electric current will not increase the types of corrosion products,but will accelerate the formation of basic copper chloride.Secondly,Ag-graphene composite coating is prepared by composite electrodeposition technology.The problem of poor dispersion of graphene in water medium was solved by the method of dispersant compounding.And the best dispersant formulation is determined as SDBS（0.6%）,TW20（1.5%）and PVP（1.5%）.The effects of additives and plating conditions on the cyanide-free silver plating were investigated by using the orthogonal optimization formula（succinimide 80 g/L,AgNO3 40 g/L,and potassium pyrophosphate 120 g/L）.The optimum technological conditions were as follows:compound surfactant 15%,graphene concentration below 1.5 g/L,current density 0.60 A/dm2,plating temperature 35°C.Finally,the structure and properties of Ag-graphene composite coatings were characterized.The good adhesion of Ag-graphene composite coating has been proved by the lattice method and thermal shock method.In the anti-tarnish Na2S impregnation experiment,there is no tarnish corrosion on the surface of Ag-graphene composite coating.The results of potentiodynamic polarization curve test in the neutral,acidic and alkaline media show that the addition of graphene can reduce the self-corrosion potential of silver plating in neutral media.According to the result of passivation potential and current density,silver-graphene composite coating is easy to form the passivation film to prevent further corrosion.In acidic medium,the addition of graphene can greatly reduce the self-corrosion current density of silver coating and improve the corrosion resistance.In alkaline medium,the addition of graphene can make the self-corrosion potential of silver plating move forward,and reduce the self-corrosion current density,indicating that it has good alkaline corrosion resistance.The hardness of Ag-graphene coating obtained by microhardness test reached 125 HV,which is nearly 50%higher than that of the commercial silver coating.and the hardness of self-made silver coatings reach 120 HV.These values of hardness meet the national requirements and industry standards.The wear resistance test results show that the Ag-graphene composite coating has low average friction coefficient and minimum wear scar width,which proves that it has excellent wear resistance and wear resistance.In addition,the contact resistance test shows that the addition of graphene has no obvious effect on the contact resistance of the silver plating layer,and it still has excellent conductivity.The results show that the corrosion behavior of contact materials under electric current is different from that of common corrosion.The new electrical contact material with graphene in silver plating layer has a good application prospects in high voltage disconnectors,which is of great significance to improve the safety of power grid operation. |
