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Grounding device is a necessary facility to ensure working grounding, lightning protection grounding and protective grounding in power plants, substations and communication stations. For the consideration of experience, the grounding device is generally made of galvanized carbon steel (flat steel, round steel). Because the grounding device has been in the bad underground environment for a long time, the chemical and electrochemical corrosion of soil is inevitable, and it also bears the corrosion of stray current and stray current of grounding grid. Therefore, ensuring the grounding grid from corrosion is the main measure to ensure the stable and safe operation of power grid.
In the anti-corrosion measures of grounding grid, cathodic protection is a scientific and feasible method. For the grounding grid already in operation, especially in coastal and humid soil areas, the cathodic protection for the grounding grid with serious electrochemical corrosion has the advantages of simple construction, low investment and good protection effect, which can not be replaced by other methods.
Design points of sacrificial anode cathodic protection for grounding grid:
1. Measure the soil resistivity of the place where the grounding grid is located, and measure the soil resistivity under different time and climate conditions to obtain the variation range of the resistivity;
2. According to the soil resistivity, the type of sacrificial anode is determined. When the soil resistivity is greater than 158 ohm (or 208 Ohm), zinc anode is selected; when soil resistivity is 1008 ohm, magnesium anode is selected; when soil resistivity is greater than 1008 ohm meter, except for special circumstances, ribbon magnesium anode is used, sacrificial anode (i.e. external current) is not used;
3. Determine the minimum protection current density (MA / m2) of grounding grid. The minimum protection current density of grounding grid should be determined by soil corrosivity (soil resistivity, redox potential), which is generally 10 ~ 50 MA / m2;
4. The total protected area is calculated according to the overall size and total length of carbon steel used in the grounding grid, and the total cathodic protection current required is calculated according to the selected protection current density;
5. Determine the cathodic protection potential of grounding grid. The cathodic potential of grounding grid is at least - 850mv, or the natural corrosion potential of grounding grid is negatively shifted by 250-300mv. For sacrificial anode cathodic protection, under the premise of ensuring the minimum protection current density, it is not necessary to consider the over protection problem;
6. Calculate the anode grounding resistance and output current, calculate the required anode weight according to the design life of cathodic protection, and then calculate the number of anode to be arranged according to the weight of single anode;
7. Choose the packing material of sacrificial anode and determine the anode embedding mode (vertical or horizontal);
8. Determine the test system of cathodic protection.
The design of cathodic protection with warm current on the grounding grid is basically the same as above except that the potentiostat and auxiliary anode are selected according to the total protection current of grounding grid. Since carbon steel of grounding grid is generally uncoated, it is not necessary to consider the problem of coating shedding due to reaching hydrogen evolution potential. However, for economic consideration, the measured protection potential should be no less than - 1.115v (the above potentials are referred to as Cu / CuSO4).
Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing corrosion protection, cathodic protection technology, engineering design, installation and technical services.