Types of Overhead Conductor

An overhead conductor carries current between line supports in a transmission or distribution system. Selection must satisfy electrical loading, operating temperature, sag, creep, wind and ice loading, vibration, corrosion, fittings, structure capacity, clearances, installation method and lifecycle cost.

1. Its electrical conductivity and area must keep losses, voltage drop and temperature within design limits.
2. Its rated strength, fatigue performance and creep behaviour must suit span, tension, weather and safety factors.
3. Low mass can reduce structural loading, but diameter and aerodynamic behaviour also affect wind and ice loads.
4. Total installed and lifecycle cost must include conductor, fittings, supports, losses, maintenance and replacement.

Types of Overhead Conductors

Hard-drawn stranded copper served many early overhead lines and remains useful in some applications. Aluminium-based conductors became common because aluminium has much lower density and often lower material cost. The selected conductor still depends on the complete line design rather than material alone.

1. Aluminium often costs less and weighs less than copper for a required line design.
2. For the same resistance, aluminium needs a larger area and diameter. The larger diameter can reduce surface electric stress and corona for the same current duty, subject to conductor geometry.

Corona: Corona begins when the electric field at the conductor surface exceeds the local inception strength of air. It depends on voltage, conductor diameter and surface condition, phase spacing, air density and weather. It can produce power loss, audible noise, radio interference, visible glow and ozone around the conductor.
Compared with copper, aluminium presents these design trade-offs:

1. Pure aluminium has lower conductivity, so a larger cross-sectional area is needed for similar resistance.
2. The larger diameter changes wind and ice loading, vibration behaviour, clearances, fittings and support design.
3. Unreinforced aluminium has lower strength and greater creep than many alternatives, which can increase sag for a comparable span and tension.
4. Aluminium’s density is about 2.7 g/cm³ versus about 8.9 g/cm³ for copper. This lower mass is an advantage, but it does not remove the other mechanical checks.

All-aluminium conductors, aluminium alloys and reinforced constructions provide different balances of conductivity, strength, sag, corrosion performance, mass and cost.

AAC (All Aluminium Conductor)

• AAC consists of concentric-lay-stranded aluminium 1350 wires. It has high conductivity and good atmospheric corrosion resistance but lower strength than reinforced or alloy conductors, so it is commonly considered for shorter distribution spans.
• Its conductivity is a material property and does not improve at lower voltages. For the same area, AAC generally has lower resistance than AAAC or ACSR because all strands are high-conductivity aluminium.
• Installed cost relative to ACSR depends on size, span, supports, fittings, losses, supply and local standards.

ACAR (Aluminium Conductor, Aluminium-Alloy Reinforced)

• ACAR combines aluminium 1350 wires with aluminium-alloy 6201 reinforcement. With no steel core, it can offer good corrosion performance where galvanic or steel-core corrosion is a concern.
• It provides a selectable balance of conductivity, strength and mass. Price and suitability must be compared for the required construction rather than treated as universally cheapest or most expensive.

AAAC (All Aluminium Alloy Conductor)

• AAAC uses aluminium-alloy strands throughout, commonly 6201 alloy under the applicable product standard.
• It offers higher strength than AAC and good strength-to-weight performance without a steel core. Its strength is not automatically equal to every ACSR construction.
• The alloy improves mechanical performance but has lower conductivity than aluminium 1350, so electrical and economic comparisons must use actual conductor data.
• Its higher strength can support longer spans or lower sag than a comparable AAC design.
• AAAC is used in distribution, sub-transmission and transmission, including corrosive environments and selected crossings.
• Sag depends on conductor area, modulus, thermal expansion, creep, temperature, span and installed tension rather than the acronym alone.
• Its low mass and corrosion performance can reduce structure or maintenance demands in some projects, but wind loading and fittings still require a full line study.

ACSR (Aluminium Conductor, Steel Reinforced)

• ACSR places high-conductivity aluminium strands around a coated steel core. The core supplies much of the tensile strength, making ACSR suitable for many long-span and high-load applications. Core size, coating and strand count vary by design.
• Construction is often described by aluminium and steel strand counts, but notation is not universally x/y/z with z as strand diameter. Use the applicable standard, code word and dimensional table.
• Stranding makes the conductor flexible. This helps during manufacture and installation, while the individual wires limit the effect of a single break. Ordinary concentric stranding does not eliminate skin or proximity effects.
• Common constructions use several strand counts and layer arrangements. Selection depends on required area, strength, diameter, sag, vibration and fittings.
• Expanded ACSR uses a lightweight or nonmetallic filler or another expanded construction to increase outside diameter without a proportional increase in conducting area. The exact design must follow its product specification.
• The larger diameter reduces surface electric stress and can reduce corona-related loss, audible noise and radio interference. Thermal rating, wind loading, sag and mechanical performance still require separate checks.

IACS (International Annealed Copper Standard)

• IACS is a conductivity reference rather than a type of overhead conductor or a copper-purity measure. A rating of 100% IACS is about 58 MS/m at 20°C, and other conductor materials are commonly rated as a percentage of that value.