The core of calculating the current-carrying capacity of aluminum wire is a heat balance problem, i.e., the balance between the heat generated by the wire during energization and the heat dissipated to the environment. Therefore, all environmental factors affecting heat dissipation efficiency will have an impact on its current-carrying capacity, which are specified as follows:
Ambient Temperature: This is the core environmental factor affecting the current-carrying capacity of aluminum wire. Generally, the lower the ambient temperature, the larger the temperature difference between the wire and the outside, the higher the heat dissipation efficiency, and the greater the current-carrying capacity; conversely, the higher the ambient temperature, the more difficult the heat dissipation, and the smaller the current-carrying capacity. For example, the safe current-carrying capacity of JL/G1A - 300/40 aluminum conductor steel-reinforced (ACSR) is 735A at 25℃, but drops to 595A at 40℃. In general calculations, the reference ambient temperature is usually taken as 25℃. When the actual temperature deviates from this value, the current-carrying capacity needs to be corrected.
Wind Speed and Direction: Wind speed directly determines the effect of convective heat dissipation and has a significant impact on current-carrying capacity. The higher the wind speed, the more intense the air flow, the faster the heat on the wire surface can be taken away, and the higher the current-carrying capacity. Data shows that the current-carrying capacity of aluminum wire at a wind speed of 0.5m/s is 40% higher than that at 0.1m/s, and at a wind speed of 1.0m/s, it is 15%–20% higher than that at 0.5m/s. Meanwhile, different angles between the wind direction and the wire will also change the heat dissipation effect. For instance, in headwind or crosswind conditions, the contact between air and the wire surface is more sufficient, and the heat dissipation is better than that in tailwind conditions, which in turn affects the calculation result of current-carrying capacity.
Solar Irradiance: Solar radiation will make aluminum wire absorb additional heat, leading to an increase in wire temperature, which then reduces the heat dissipation margin and lowers the current-carrying capacity. The stronger the solar irradiance, the more obvious this impact is. For example, the current-carrying capacity of aluminum wire at a solar irradiance of 100W/m² is 15%–30% higher than that at 1000W/m²; however, when the solar irradiance decreases slightly from 1000W/m² to 900W/m², the current-carrying capacity only increases by 1%–4%, indicating that small changes in the high solar irradiance range have limited impact on the current-carrying capacity.
Soil Thermal Resistivity: This factor is mainly applicable to aluminum wires laid directly underground. The smaller the soil thermal resistivity, the stronger the thermal conductivity, the better the heat dissipation effect of the wire, and the greater the current-carrying capacity. For example, moist clay has a dense structure, low thermal resistivity and good heat dissipation performance; while dry sandy soil has many pores, high thermal resistivity and poor heat dissipation. For instance, when the soil thermal resistivity is 1.5K·m/W, the current-carrying capacity correction coefficient is about 0.85, which is significantly lower than the current-carrying capacity under the standard thermal resistivity of 1.2K·m/W.
Surrounding Heat Sources: If the aluminum wire is close to high-temperature equipment such as boilers and transformers, the heat emitted by these devices will increase the local temperature around the wire and interfere with the normal heat dissipation of the wire. In this case, the actual current that the wire can carry will be lower than that without surrounding heat sources. When calculating the current-carrying capacity, the impact of these additional heat sources needs to be considered separately, and the current-carrying capacity should be appropriately reduced to ensure safety.
