The difference between copper and aluminum transformers is also determined by the difference in materials, which is specifically reflected in the following aspects:
1) The resistivity of copper conductors is only about 60% of that of aluminum conductors. In order to achieve the same loss and temperature rise requirements, the cross-sectional area of aluminum conductors required is more than 60% larger than that of copper conductors, so the same capacity and the same parameters Under the condition, the volume of aluminum conductor transformer is usually larger than that of copper conductor transformer, but at this time, the heat dissipation area of the transformer has also increased, so it has a lower oil temperature rise;
2) The density of aluminum is only about 30% of copper, so aluminum conductor distribution transformers are lighter than copper conductor distribution transformers;
3) The melting point of aluminum conductors is much lower than that of copper conductors, so its temperature rise limit in short-circuit current is 250°C, which is lower than 350°C of copper conductors. Therefore, its design electrical density is lower than that of copper conductors, and the cross-sectional area of transformer conductors is higher. Large, so the volume is larger than that of a copper conductor transformer;
4) The hardness of aluminum conductors is low, so burrs on its surface are easier to eliminate. Therefore, after being made into a transformer, the probability of short circuit between turns or layers due to burrs is reduced;
5) Due to the low tensile and compressive strength and poor mechanical strength of aluminum conductors, aluminum conductor transformers are not as capable of withstanding short circuits as copper conductor transformers. When performing dynamic stability calculations, the stress of aluminum conductors should be less than 450kg/cm2, while copper conductors The stress limit of the conductor is 1600kg/cm2, which greatly improves the bearing capacity;
6) The welding process between aluminum conductors and copper conductors is poor, and the quality of joint welding is not easy to guarantee, which affects the reliability of aluminum conductors to a certain extent.
7) The specific heat of the aluminum conductor is 239% of that of the copper conductor. However, considering the difference in density and design density between the two, the actual difference in thermal time constants between the two is not as large as the difference in specific heat indicates, so it is The short-term overload capacity of dry-type transformers has little impact.