Applied Research Of Stainless Steel-clad Q235 In The Grounding Grid

The substation grounding grid is one of the main equipment in substation,which mainly plays roles of preventing lightning,static electricity,discharge,and work discharge.Galvanized steel is often used as a ground material in our country,however,which is prone to severe corrosion,resulting in decrease of cross-section,lack of thermal stability and increaseof grounding resistance.So it has been unable to meet the ground safety requirements for of the system,especially in the high voltage level and highly corrosive soil regions.The stainless steel has good corrosion resistance,but the conductivity is less than ordinary carbon steel,which is unfavorable for the discharge of grounding grid.Aiming at this reality,this paper takes the Q235 carbon steel as substrate and 304 stainless steel as cladding material to prepare the new ground material of stainless steel-clad Q235 by hot-rolled and compounding method.The fcasibolity of stainless steel-clad Q235 as new ground material was analyzed through modern materials analysis and testing technology,thermal shock test and fault current impact test.Meawhile,its corrosion perfurmance in four typical soils such as mud rock soil,lness,saedy soil,saline soil was inspected by soil corrosion experiments and electro-chemical method.The results of the study show that:(1)The transitic zone of stainless steel-clad Q235 prepared by hot-rolled method has good metallurgical bonding characteristies;In the range of measurement of buried 10～55cm,the average ground resistance of stainlss steel-clad Q235 is about 0.76 times that of galvanized steel:After two thermal shocks at 400℃ and 800℃.the sample surface have no bubble and crack.And after the fault current shock,there is also no bubble and crack on the sample surface.(2)Static corrosion results show thar the corrosion resistance of 304 stainless steel os better than galvaized Q235,thus 304 stainless steel can solve the problem of poor acid resistance of galvanisd Q235 and suit for grounding grid composites;Cl-and salt content in the soil are the main influence factors of soil carrosion,soil’s caustic performance is as follow;unline soil loess>sandy soil>mud rock soil;Corrosion resistance of the grounding material is sa follow;304 base metal>304 welding seam.(3)DC discharge have a serious impact on the corrosion of grounding grid materials,and with the increase of applied DC current,the corrosion rate grows following a linear law approximately.The corrosion rate in Saline soil has the most significant growth.For example,when applied 200A/m2 DC,the corrosion tate increased about 6 times compared with the black group.The caustic performance of four soils to the general trend is as folloe:saline soil>loess>mud rock soil>sandy soil.(4)Corrosion caused by AC discharge is less than DC discharge,for there is obvicus passivation phenomenon in the polarization curve compared with the blank group.When applied 20mA and 40mA AC,the current density of the ground material is less than the blank group;Rp of the ground material in four soils follows this rule:Rp(200A/m2)>Rp(400A/m2)>Rp(600A/m2)>Rp(0A/m2),suggesting that a small AC current can generate films to slow down the corrosion.The caustic performance of four soils to the general trend is as follow:saline soil>loess>mud rock soil>sandy soil.(5)After Chemical immersion for 30 days,the Rp of stainless steel-clad galvanized Q235 in mud rock soil,loess and sandy soil is greater than that of stainless steel-clad Q235;the Rp of stainless steel-clad galyanized Q235 in saline soil than that of stainless steel-clad Q235,It indicates that the zine layer can play the role of sealing agent to cope with the general corrosion cnvironment,but not suiable for use in high salt content of saline land area.Its preparation will be our next research topic.