Copper clad steel is the most suitable new grounding material. Compared with traditional grounding materials, it has advantages in the following aspects: corrosion resistance; conductivity; construction difficulty; welding reliability. This paper mainly introduces corrosion resistance and conductivity.
1. Corrosion resistance: The corrosion resistance of grounding body directly determines the service life of substation grounding network. There are two main forms of corrosion of grounding body: surface corrosion and pitting corrosion. Surface corrosion refers to uniform corrosion, which is related to the material and soil corrosion performance of grounding body, and its speed is relatively stable. Point corrosion mainly exists in joints and other parts which are prone to electrochemical corrosion. The rate of point corrosion is 4 to 60 times that of uniform corrosion, which is the main form of corrosion threatening the safety of grounding grid.
The anti-corrosion ability of steel itself is very poor. The steel grounding body is mainly protected by external galvanizing. If there is insufficient protection for the damaged plating such as welding points in the construction process, it is very easy to form point corrosion. Steel grounding grids in substations usually need to be transformed and replaced in ten years, and seldom work steadily for fifteen years. It is useless to increase the cross section of grounding pole by a large margin, because the pitting corrosion speed is too fast, and it is easy to erode and break the horizontal grounding network.
The corrosion rate of copper grounding body in soil is about 1/10-1/50 of steel. The corrosion product of copper material is basic copper carbonate, which will be adsorbed tightly on the surface of copper material to prevent further corrosion and to protect copper material from pitting corrosion. When the coating is reasonable, the corrosion resistance of copper clad steel is equivalent to that of copper. Copper or copper-plated steel grounding grids can operate stably for up to 50 years.
2. Conductivity: The conductivity of grounding material directly affects the power frequency resistance and impact resistance of substation grounding network. According to the International Annealed Copper Standard (IACS), the conductivity of standard copper is 100%, that of standard steel is only 10.8%, and that of copper is about 10 times that of steel. According to the thickness of the coating, the conductivity of the copper clad steel earth rod
is about 20%-40%, which is much better than that of the steel grounding rod. In the case of high frequency lightning current impact, the skin effect of conductor is more obvious, and the high frequency conductivity of copper clad steel grounding material is more advantageous than that of steel grounding material.