1 Technical status of winding wire

Due to the relative scarcity of copper resources in China, the national policy advocates "saving copper with aluminum" and reduces the dependence on imported copper by expanding the application of aluminum. The consumption of aluminum conductors in the cable industry in 2022 has reached 2.2 million tons, a significant increase over previous years. As far as the winding wire industry is concerned, the annual consumption of aluminum conductors has increased to about 300,000 tons, a significant increase. Rectangular aluminum transposed winding wire is also used in the equipment such as flat wave device and reactor for UHV and long distance transmission, and in the "high-speed car" (1000 km/h). The main reasons for the increase in the application of aluminum winding wires are: in terms of electrical conductivity and mechanical strength, aluminum conductors have many gaps compared with copper conductors. This difference limits the application of enamelled aluminum wire, especially in large motors, transformers, and other important applications. However, in terms of insulation performance, the Al2O3 protective film formed after the oxidation of the surface of the aluminum conductor has a relatively small impact on the insulation performance, while the copper oxide formed after the oxidation of the copper conductor will have a catalytic effect on the thermal aging process of some polymer insulation materials, accelerating the aging of insulation materials. Therefore, under the same insulation conditions, the winding wire using aluminum conductor compared with the winding wire using copper conductor, its heat resistance level can be increased by about 20 ℃. 

2 Technology development trend

With the technological development of electrical equipment such as motors, transformers and sensors, the winding coils used in order to meet the needs of miniaturization and high power, the heat resistance level of winding wires needs to be gradually improved. Traditional enamelled wire, film wrapping wire with copper, aluminum as conductor, polyester, polyurethane, polyester imide, polyimide as insulation enamelled wire, film wrapping wire, the highest heat resistance of 240℃. When the long-term use temperature (generally taking the temperature index as a reference, the service life is required to be no less than 20000h) requires more than 240 ° C, in order to prevent the conductor from oxidizing too quickly, the coating is usually used to protect the copper conductor. For insulation materials, organic and inorganic composite insulation is usually used. For use at temperatures above 400 ° C, the winding wire conductor needs to be an alloy conductor, and a coating of sufficient thickness is required to protect the conductor. At this time, the insulation can only be inorganic insulation. At present, there are relatively few studies on winding wires that meet the requirements of long-term heat resistance at temperatures above 600℃. Due to the conductor softening, conductor active particle diffusion, insulation failure and other phenomena of the theoretical research is very few, has not formed a relatively mature solution.