AAC CONDUCTOR: Powerful for Low Voltage Distribution

AAC conductor or All Aluminium Conductor is basically a stranded conductor that is made up of hard drawn aluminium wires. AAC conductors finds wide application in the power distribution networks, with shorter pole span, high conductivity and reduced line loss becomes the priority. All Aluminium Conductor is a light weight, easy to install conductor, offering high current carrying capacity due to its excellent conductivity, which is 61% of IACS (International Annealed Copper Stranded) or 35.5 MS/m (Mega-Siemens per meter). Although it is an excellent electrical conductor but, lacks in mechanical strength, which limits it’s usage in areas with high wind and ice loadings.

Construction of AAC conductor

The construction of AAC conductor is simple and optimized with uniform and high electrical conductivity all across. The AAC conductor is entirely made from hard drawn aluminium strands with no steel cores or any mix of alloy. All the aluminium strands are work hardened during the drawing process, complying with the IEC 61089 or ASTM B231 standard. The aluminium strands are round in shape, layered helically in one or more concentric layer formation around a central strand. The number of the concentric layer depends on the conductor size and required. Single layered concentric stranding can be seen in smaller sizes of AAC conductors, while the larger ones uses multiple concentric layers.

Each strands of aluminium is drawn from highly pure aluminium EC grade so that the strength is increased and the diameter remains uniform. The strands are then stranded together with a precise lay length in order to achieve flexibility and mechanical stability. Since, no steel core is used, AAC conductor becomes lighter than other conductors. The absence of non conductive metal makes the cross section of the conductor 100% aluminium with excellent electrical conductivity.

The smooth surfaces of the AAC conductor make installation easy and lowers the corona loss in low to medium voltage lines. The construction of AAC conductor is done entirely from aluminium, which naturally forms a thin aluminium oxide layer (AL₂O₃). This oxide layer acts as a protective coating, giving AAC a good resistance to atmospheric corrosion. Although it has a low tensile strength, its lightweight construction, high electrical conductivity makes it ideal for short span distribution network typically between 40- 80 m with moderate mechanical loading.

Properties of AAC conductor

Mechanically, AAC conductor is stranded from hard drawn aluminium wires and has a tensile strength in the range of 90 to 110 MPa. It provides the conductor enough strength for urban overhead lines with less mechanical loading. Although it is not as strong as other conductors, the less weight of the conductor helps with the installation ease. The modulus of elasticity of the conductor is around 60 to 70 GPa, which ensures moderate stiffness.

More the stiffness of the conductor, less is the sag (controlled), swing during wind gust also affects the conductor. The conductor has a elongation at break of around 3% which is considered moderate ductile. With this property the conductor can stretch slightly before breaking (3% of original length). The low density of aluminium (2.703 g/cm³) makes the AAC conductor lightweight. This reduces the mechanical tension of the conductor because of self-weight, and lowers the sag sensitivity.

Electrically, AAC conductor offers superior performance because of 100% aluminium cross section that maximizes the electrical conductivity. With a resistivity of less than 0.028264 Ω·mm²/m at 20°C, the AAC achieves a conductivity equivalent to 61 % of IACS, ensuring low power loss in the distribution circuit. Although, the AC resistance slightly increases because of the skin effect but still low enough to maintain efficient current flow. AAC conductor has a continuous operating temperature limit in the range of 75-85 °C, which supports reliable performance in low to medium voltage urban network.

Application

Low voltage overhead distribution: AAC is widely used for low voltage overhead distribution of power in rural and urban areas for its superior electrical conductivity, light weight, ease of installation, and suitability for short and lightly loaded spans.

Short span line: AAC conductor is ideal for construction of lines with short spa, where the mechanical loading is low. It’s light weight feature, flexibility and high electrical performance makes it ideal for compact and localized power distribution network.

Areas with industrial pollution: Coastal or industrial areas, where other conductor fails, AAC conductor’s performance remains unaffected because of the thin aluminium oxide layer formed at the surface which resists the salty coastal atmosphere, industrial pollutants.

Suitable for tight and congested areas: AAC is very effective in congested corridors because of its light weight nature and flexibility, the operation and maintenance of the circuit becomes easy even at congested areas. It also allows easy rounting in tighter areas, meeting the power distribution needs.

Types of AAC

Based on IEC standard

Based on ASTM standard

Advantages and Limitations

AAC vs AAAC vs ACSR

This article is a part of the Cables and Conductors, where other articles related to the topic are discussed in details.