Characteristics and Application of Copper Clad Aluminum Cables for Hardware Wires and Cables

[China Aluminum Network] For the electromechanical installation industry, wire and cable occupy an important position in the electromechanical installation project. As its main raw material, copper accounts for 70%~80% of the total cost of cable products, and the price of copper cables will increase. The rapid increase in copper prices has brought great difficulties to investors and contractors in terms of project cost control. For this reason, the research and application of copper-clad aluminum cables has grown rapidly.

The copper clad aluminum cable refers to the wire and cable that uses aluminum core wire instead of copper to become the main body of the cable and a certain proportion of copper layers outside. Copper clad aluminum cables can be divided into two categories based on their use: one is copper clad aluminum cable for signal or communication purposes, and the other is copper clad aluminum cable for power supply. With regard to its characteristics, the following comparisons are made between copper clad aluminum and pure copper cables.

First, copper clad aluminum communication cable mechanical properties. Pure copper conductors have higher strength and elongation than copper-clad aluminum conductors, which means that pure copper has better mechanical properties than copper clad aluminum. From the perspective of cable design, pure copper conductors have better mechanical strength than copper-clad aluminum conductors, and are not necessarily needed in practical applications. The copper clad aluminum conductor is much lighter than pure copper, so the copper clad aluminum cable is lighter in weight than the pure copper conductor cable, which will facilitate the cable transportation and cable construction. In addition, copper clad aluminum is softer than pure copper. Cables made of copper-clad aluminum conductors are somewhat softer than pure copper cables.

Electrical performance. Because the electrical conductivity of aluminum is worse than that of copper, the DC resistance of the copper clad aluminum conductor is larger than that of the pure copper conductor. This has no effect. It depends mainly on whether the cable will be used for power supply, such as power supply to the amplifier, if it is used for power supply. Copper-clad aluminum conductors will result in additional power consumption and more voltage drop. When the frequency exceeds 5 MHz, the AC resistance decay at this time is not significantly different between the two different conductors. Of course, this is mainly due to the skin effect of high-frequency currents. The higher the frequency, the closer the current flow is to the surface of the conductor. Actually pure copper material on the surface of the copper-clad aluminum conductor, when the frequency is high, the whole current plating Flowed in the copper material. At 5 MHz, the current flows in a thickness of approximately 0.025 mm near the surface, while the thickness of the copper layer of the copper-clad aluminum conductor is approximately one time greater than this thickness. For coaxial cable, the transmission effect of the copper-clad aluminum conductor and the pure copper conductor is the same because the transmitted signal is above 5 MHz. The attenuation of the actual test cable can prove this. The copper clad aluminum is softer than the pure copper conductor and can be easily straightened in the production process. Therefore, to a certain extent, it can be said that the copper clad aluminum cable is better than the cable with the pure copper conductor.

Economical. Copper-clad aluminum conductors are sold by weight, and pure copper conductors are sold by weight. Copper-clad aluminum conductors are more expensive than the same weight of pure copper conductors. But the same weight of copper clad aluminum is much longer than the length of pure copper conductor, and the cable is calculated by length. The same weight, copper clad aluminum wire is 2.5 times the length of the copper wire, the price is only a few hundred dollars more per ton. Combined, copper clad aluminum is very advantageous. As the copper-clad aluminum cables are relatively light, the cable transportation costs and installation and installation costs will be reduced, which will bring certain convenience to the construction.

Second, copper clad aluminum power cable DC resistivity. The resistivity of the copper clad aluminum wire is larger than that of the pure copper wire, which is about 1.5 times that of the pure copper wire. When the negative value is the same, the weight of the copper clad aluminum wire is about 1/2 of that of the pure copper wire. According to the skin effect calculation, the resistivity is equal to that of a copper conductor of the same cross section at a high frequency of 5 MHz or more. In the use of a 50Hz frequency power cable, the skin effect and proximity effect of the copper conductor gradually become prominent above 150mm2, and due to continuous development of science and technology, generation of higher harmonic currents and energy will be injected into the power supply system. High harmonic voltage of the corresponding frequency is generated on the impedance of the system, resulting in distortion of the waveform of the voltage, increasing the loss of the power supply system and increasing the heating of the conductor; in addition, the cable amplifies the harmonics and generates overvoltage at the joint. Damaged cable ends. The use of copper-clad aluminum conductors acts to reduce the AC impedance (resistance) produced by higher harmonics. In other occasions, by increasing the volume of copper in the copper clad aluminum monofilament and corresponding technological measures, the copper clad aluminum/copper composite conductor meets the DC resistance requirements of the conductor within the upper limit of the existing outer diameter of the same specification conductor.

Connection method. The use of copper-clad aluminum conductors can meet the current practice of product selection, design, use, and installation of wire and cable that will continue for many years, and it is also advantageous for tight pressing and tin soldering of cable terminals.

Reduce AC resistance. AC resistance is the main basis for current carrying capacity. According to the principle of skin effect, the current per unit area of ​​a single conductor is larger than the current per unit area of ​​the center of the conductor, that is, the center of the large conductor. In the circular area where the same conductors are formed, the center of the circle is smaller than the current passing through the circle. Therefore, it is reasonable and economical to use a different metal for the center conductor and the circle conductor. In addition to the DC resistance and skin effect, there are proximity effects that affect the AC resistance index. Compared to the copper conductor with the same DC resistance, after using a copper composite conductor, a single conductor, aluminum is in the center and copper is on the outer edge; In the combined conductor, the inner layer is copper clad aluminum and the outer layer is pure copper, while aluminum has no copper sensitivity to skin effect and proximity effect. At the same time, the copper composite conductor increases the total cross section of the conductor, thus increasing the number of conductors. The surface area improves the cooling conditions of the cable and increases the heat dissipation area. The thermal conductivity of aluminum is similar to that of copper. Under the same material cost conditions, the AC resistance index is much more economical.

Good corrosion resistance: Aluminum is more easily corrosive than copper, but due to the complete metallurgy of the copper clad aluminum material, the aluminum is completely covered with copper and will not be contacted by water and air, achieving the same performance as copper. The copper-clad aluminum/copper composite conductor is also more conducive to avoiding poor contact between the conductor and the terminal due to corrosion, bumps, or poor soldering due to corrosion, scratches, or heat generation. The potential difference between the metal forms, accelerates electrochemical corrosion, and causes the hidden danger of the cable ends to burn out. For aluminum conductors, especially in coastal areas, the chloride ions contained in the salt spray in the atmosphere will condense on the surface of aluminum, causing local corrosion around the surface impurities and defects, forming holes, cracks and micro-cells, exacerbating the aluminum conductors. corrosion.

Low cost and light weight. Copper-clad aluminum conductor cables can save more than 40% of the cost compared with copper cables of the same specifications. Copper-clad aluminum/copper composite conductor cables can save costs by more than 20%. The proportion of copper clad aluminum wire is only 37%-40% of pure copper wire. With a wire diameter and weight equal to 2.5 times the length of the pure copper wire.

Good weldability. The copper clad aluminum wire is coated with a layer of pure copper concentrically, so it has the same solderability as the pure copper wire and is convenient for production.

Although copper-clad aluminum cables have been born and are gradually being applied, there is still a lot of resistance. The main performance of copper-clad aluminum cables is that it is difficult to find the application basis of the country and industry, and it is difficult to obtain the approval of the design unit. Copper Clad Aluminum Cables There are still quite a number of products that do not yet have 3C certification. The industry is still in the stage of product identification and the establishment of corporate standards. The product specifications, characteristics, and standards of use vary greatly between brands, and it is difficult for engineering designers to apply them. Grasping, the investor is not happy to accept it at the moment.

However, with the gradual improvement and recognition of national standards and regulations, copper-clad aluminum cables will surely become more standardized, which will undoubtedly become the bright spot of wire and cable in the next few years and will drive the development of the entire industry.