In addition to its advantages in corrosion resistance and electrical conductivity, copper-clad steel grounding materials have certain advantages over traditional galvanized materials in terms of thermal stability, construction difficulty and welding reliability.
1. Thermal stability: The cross-sectional area of grounding material mainly depends on its thermal stability. The thermal stability coefficient C of materials characterizing the thermal stability of materials. The thermal stability coefficient of copper is 210, steel is 70, and 30% copper-plated steel strand is about 176. Under the same short-circuit condition, the required cross-sectional area of steel grounding body is three times that of copper and 2.5 times that of 30% copper-clad steel strand.
2. Construction difficulty: In substation grounding design, galvanized flat steel is generally used as horizontal grounding grid material and galvanized angle steel as vertical grounding grid material. Copper-clad steel strands are generally used as horizontal grounding materials and copper-plated round steel as vertical grounding poles. The length of galvanized flat steel is limited by the length of galvanized trough, and the length of each trough is not more than 6 m. The length of horizontal grounding network in substation is usually about 100 m to 300 m. When the whole grounding network is laid, a large number of lap joints will be produced. The length of each wire of copper-plated steel strand can reach 200 m, which can greatly reduce the number of joints, not only reduce a lot of construction, but also improve the reliability of the system. As a vertical grounding electrode, copper clad steel round earth rod
is easier to penetrate into the deep soil than galvanized angle steel, and the grounding construction is more convenient.
3. Welding reliability: The overlap of galvanized flat steel mainly depends on arc welding. Because of the high temperature of welding joint, the welding arc is directly exposed to air. When air intrudes, liquid metals undergo intense oxidation, nitridation and evaporation. Moreover, the hydrogen atoms decomposed by the moisture in the air at high arc temperature can dissolve into liquid metal, resulting in hydrogen embrittlement, reduction of plasticity and toughness, and even cracks. In addition, due to the direct exposure of solder joints to air during manual welding, the cooling rate after welding is very fast, and various metallurgical reactions are difficult to reach equilibrium state. The chemical composition of the weld is not uniform, and the gas and oxide in the molten pool are too late to float. It is easy to form defects such as blowhole and slag inclusion, resulting in virtual welding or impermeability of welding, affecting the conductivity of the grounding body. At the same time, the quality of arc welding is greatly affected by the technology of welding workers, and there are many unstable factors.