When the current passes through the resistance of the stainless steel tube, the current does work to consume electric energy and generate heat. This phenomenon is called the heating effect of the current. There is a strong alternating magnetic field in the space around the high-current conductor, and the steel components located in it generate heat due to eddy current and hysteresis loss. For steel structure forming a closed magnetic circuit, such as carbon steel casing, structural steel frame, etc., it is also possible to induce circulating current and generate heat. This loss and heat will increase sharply with the increase of the current of the cable, which will damage the cable insulation layer in the electrical bushing and affect the safe operation of the power supply system. In order to improve the generation of loss and circulation heat, prevent the closed magnetic circuit formed by the cable through the wall bushing and steel components, so as not to affect the cable insulation loss and affect the safe operation of the system.
The traditional method of using a magnetically conductive steel pipe to pass through a single-core cable to avoid the formation of a circular current is to cut a gap in the steel sleeve along the longitudinal direction to block the magnetic circuit, but this method is not suitable for occasions that require airtight waterproofing. The more direct method is to use non-magnetic material composite sleeves to replace steel sleeves and steel parts, but the mechanical properties, heat resistance and oxidation resistance of composite materials are poor. Copper, aluminum, aluminum alloy and other non-magnetic metal materials are too expensive to be economical for engineering construction. Combined with the actual situation of the substation: mechanical strength, anti-corrosion, no eddy current requirements, etc., the effective way to improve the above problems is to use austenitic stainless steel casing and austenitic stainless steel plate to avoid the formation of a closed magnetic circuit and prevent circulation heating produce.
Stainless steel is steel that is not easy to rust. In fact, some stainless steel has both stainless and acid resistance (corrosion resistance). Austenitic stainless steel is a stainless steel with an austenitic structure at room temperature. When the steel contains about 18% Cr, Ni8~10%, and C about 0.1%, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the famous 18Cr-8Ni steel and high Cr-Ni series steel developed by adding Cr and Ni content and adding Mo, Cu, Si, Nb, Ti and other elements on this basis. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low, it is impossible to strengthen it through phase transformation, and it can only be strengthened by cold working. If S, Ca, Se, Te and other elements are added, it has good machinability. In addition to the corrosion resistance of oxidizing acid medium, this kind of steel can also resist the corrosion of sulfuric acid, phosphoric acid, formic acid, acetic acid and urea if it contains elements such as Mo and Cu. If the carbon content in this type of steel is less than 0.03% or contains Ti and Ni, its resistance to intergranular corrosion can be significantly improved. High-silicon austenitic stainless steel has good corrosion resistance in concentrated nitric acid.