AAC (All Aluminium Conductor) cable is widely used in electrical power transmission and distribution networks, particularly in urban and rural settings. While it offers advantages such as a higher current-carrying capacity compared to some other conductors of the same size, it is not always the first choice for long-distance transmission. This paradox arises due to various engineering, economic, and environmental factors. Let's explore this in detail.

Understanding AAC Cable’s Current-Carrying Capacity

The current-carrying capacity of a conductor refers to its ability to transport electric current without exceeding safe temperature limits. Several factors influence this capacity, including:

  1. Material Composition – AAC cable is made entirely of aluminum, which has a lower electrical resistance compared to other commonly used materials like steel. Lower resistance means less heat generation, allowing it to carry more current.

  2. Thermal Properties – Aluminum has good thermal conductivity, helping it dissipate heat efficiently. This prevents excessive temperature rise, enabling the cable to sustain a higher load.

  3. Surface Area and Skin Effect – Since aluminum is lightweight and can be drawn into thick strands, AAC conductors often have a larger cross-sectional area. This minimizes the "skin effect" (where AC current tends to flow more on the surface of a conductor), allowing better utilization of the available conducting material.

So, Why Isn't AAC Always the Best Choice for Long-Distance Transmission?

Despite the above advantages, AAC is not always preferred for long-distance transmission. This can be attributed to the following reasons:

1. Lower Mechanical Strength

AAC cables lack a steel core, making them significantly weaker than alternatives like ACSR (Aluminum Conductor Steel Reinforced) cables. This has multiple consequences:

  • Sagging Issues – Due to its lower tensile strength, AAC cables sag more under their own weight, especially when spanning long distances. This limits the maximum span between transmission towers.
  • Wind and Ice Loading – In regions with strong winds or heavy ice accumulation, AAC cables are prone to damage as they cannot withstand the additional mechanical stress.

2. Higher Electrical Resistance Over Long Distances

Aluminum has higher electrical resistance than copper. While AAC cables are optimized for conductivity, they still experience:

  • Higher Voltage Drop – Over long distances, the cumulative resistance causes a substantial voltage drop, leading to inefficiencies in power delivery.
  • Increased Line Losses – More electrical resistance translates to higher transmission losses, which means more power is wasted as heat rather than reaching the intended destination.

3. Reduced Efficiency for High-Voltage Transmission

For high-voltage transmission lines, efficiency is critical. AAC cables do not perform as well as alternatives like ACSR and AAAC (All Aluminium Alloy Conductor) for several reasons:

  • Heat Generation and Expansion – The resistance of AAC leads to more heat generation, which can cause thermal expansion and, in extreme cases, sagging or failure.
  • Limited Current Carrying Over Distance – Although AAC can carry high current, it is not ideal for transferring power over vast distances without significant losses.

4. Shorter Lifespan in Harsh Environments

AAC cables are more susceptible to environmental degradation. Factors that reduce their lifespan include:

  • Corrosion in Coastal or Industrial Areas – Pure aluminum oxidizes when exposed to moisture and pollutants, leading to a decrease in conductivity and structural integrity.
  • Temperature Fluctuations – In areas with extreme temperature variations, AAC cables expand and contract significantly, which can lead to mechanical fatigue over time.

5. Cost Considerations and Infrastructure Limitations

While AAC cables are relatively cost-effective in terms of material price, their limitations lead to higher costs in other aspects:

  • More Frequent Maintenance and Replacement – Due to sagging, wear, and corrosion, AAC cables require more maintenance compared to reinforced conductors.
  • Additional Support Structures – The reduced tensile strength of AAC means that more transmission towers or support structures are required, increasing infrastructure costs.

When is AAC Cable Actually the Best Choice?

Despite these limitations, AAC cables are still widely used in specific scenarios:

  1. Urban Power Distribution – In cities where shorter spans and lower mechanical stress are common, AAC cables are preferred due to their flexibility and ease of installation.
  2. Short to Medium Distance Transmission – For power transmission over moderate distances, AAC is an effective and economical choice.
  3. Low-Voltage Overhead Lines – AAC is commonly used in distribution networks operating at lower voltages where sagging and losses are not as critical.
  4. Environmentally Friendly Applications – Since AAC does not contain steel, it is sometimes chosen for applications where minimal magnetic interference is required.

Conclusion: Balancing Electrical and Mechanical Requirements

The tricky nature of AAC cable lies in its ability to carry high current while being limited by mechanical and long-distance efficiency constraints. Engineers must carefully evaluate whether its advantages outweigh its drawbacks based on the specific application.

For shorter distances and urban settings, AAC is a strong contender. However, for long-distance high-voltage transmission, conductors like ACSR or AAAC are typically the better choice due to their superior mechanical strength and reduced power losses.

Understanding these trade-offs is crucial when selecting the right conductor for a given power distribution system.