Study On Corrosion Mechanism And Anti-corrosion Measures Of Grounding Device

Electric grounding is an important safety barrier for safety operation of power generation,transformation and transmission systems. With the capacity of substation continuous expanding, it is now making higher and higher demands on stability of grounding device. HVDC is just starting in China. Corrosion of neutral grounding device as anodic becomes much fast and serious in high voltage DC. With the accident increasing by corrosion, people pay more and more attention to research on corrosion and anticorrosion of grounding device. It has become a very active topic in area of International System of Electrical at present.The corrosion location of grounding decice and its reason, the harm and environment of grounding device corrosion are analyzed in this paper. The method of research on soil corrosion is introduced. Three kinds of typical soils were used as research object in this paper. The physicochemical property of the soil was measured. Then the performances of soil corrosion were evaluated by applied with German DIN50929 synthetic evaluation method. The result was checked by comparing with the result of embedded assay. The relationship between corrosion quantity of grounding material (F) and the time (T) was obtained by fitting the embedded assay data. Influence of moisture, chloride and pH on corrosion behavior of grounding device in soil was tested by M283 potentiostat made in American EG&G Company. And the obtained conclusions were listed as follow:(1) The soil corrosion of grounding device is affect by physico- chemical property of the soil. Because these factors are interacted, many aspects must be considered when appraising the corrosive of soil.(2) The corrosive order of three kind of soils are: acidic soil> acidic silt> alkaline red soil, and the relationship between corrosion quantity of grounding material (F) and time(T) are obeying the following equation: F = AeT /C+ B.(3) When the moisture content is low, the soil corrosion of grounding device becomes small; When the moisture content is middling, the soil corrosion of grounding device becomes most serious; And when the moisture content is high, the soil corrosion of grounding device becomes weak.(4) Because the grounding device is affect obviously by the content of chloride ion, the measure must be performed to the grounding device in the area of salt-affected soil, to maintain the fixed number of enlistment year of grounding device.(5) There is a critical data between pH value and the soil corrosion of grounding device. When the critical value is approached, the soil corrosion of grounding device becomes weaken, on the contrary, it becomes reinforce.The work is helpful to reveal the mechanism of the soil corrosion of grounding device. It also offers a direction when designing grounding device and mapping out the measure of anticorrosion.Based on the all above work, one 110kV substation, which adopts sacrifice anode cathodic protection, is studied. After analyzing the main of design, the magnesia base is selected as the sacrificed anode, and the data of protected area and least protect current density are calculated, showing the inbuilt way, filling material, test prod of anode are very well. By now, there actually is no integrated design standard and no construction standard about sacrifice anode/cathodic protection in domestic grounding grid of substation. It shows a general design technique, which can afford technique sustain on the corrosion project of grounding grid for the future.This paper also indicates that the combination application of sacrifical anode/cathodic protection and high efficiency bentonite drop resistance preservative should be used at the place where anticorrosion and drop resistance are difficult to adopt. And the effect of anticorrosion will be better, filling with high efficiency bentonite drop resistance preservative around the sacrifical anode.