What is ACSR Conductor? – A Complete Explanation

ACSR means Aluminum Conductor Steel Reinforced. We mostly choose ACSR for high‐voltage overhead transmission lines. An ACSR consists mainly of two parts. It has multiple layers of pure aluminum strands for carrying current. The purity of aluminum is 99.5%. It also has a central core of galvanized steel. This core provides tensile strength to the conductor in addition. The manufacturers produce aluminum strands using the hard-drawn process with a drawing machine. Obviously, aluminum offers good conductivity. It also provides a low weight-to-volume ratio. Therefore, this composite design offers both conductivity and light weight with the required high tensile strength.

Basic Construction of ACSR Conductors

An Aluminum Conductor Steel Reinforced (ACSR) has concentric layers of strands (wires). The diameter of all the strands, including steel, is the same. The manufacturers use galvanized high-carbon steel wires for the central steel core. Then, they lay one or more layers of aluminum strands (wires) helically around this steel-reinforced core. The aluminum strands carry almost all the current. At the same time, the steel core withstands the mechanical load. Although the aluminium strands also take a small percentage of the tensile load in an ACSR conductor. The steel offers poorer electrical conductivity than aluminum. The zinc galvanizing on steel strands prevents galvanic corrosion of steel.

Applications of ACSR Conductors

Aluminum Conductors with Steel Reinforced (ACSRs) serve medium to extra‐high-voltage lines. Power transmission utilities use ACSR conductor for 132 kV, 220 kV, and 400 kV power transmission lines. Even the distribution utilities use ACSR conductors in their lower‐voltage distribution lines. According to general practice, 132 kV transmission lines use ACSR Panther conductor. On the other hand, 220 kV lines often use ACSR Zebra, Wolf, or Goat variants. Power transmission utilities also build 400 kV lines with ACSR Moose conductor.

Power utilities use Aluminum Conductors with Steel Reinforced for long river crossings and rugged terrain because of their high strength‐to‐weight ratio. They also use a special type of ACSR conductors for long river crossings or similar purposes. Additionally, power utilities commonly use ACSR conductors for AIS-strung buses, dropper connections, and jumper connections in substations.

Advantages of ACSR

• High tensile strength: The steel core provides exceptionally high mechanical strength. Hence, this allows long spans and high tensions. Obviously, the mechanical strength of ACSR is far better than that of all‐aluminum conductors.
• Good conductivity and light weight: Manufacturers use 99.5% pure aluminum to produce aluminum strands. It provides good conductivity. At the same time, it gives the ACSR conductor a lightweight design. However, aluminum has lower conductivity than copper. In contrast, it has a ‘weight per unit volume’ of only ~30% of that of copper. This yields high ampacity per weight for ACSR conductors. The combination of lightweight and high conductivity, along with mechanical strength, creates significantly less sag than all-aluminum conductors.
• Cost-effectiveness and availability: Aluminum and steel both expand relatively low compared to copper. Currently, many manufacturers produce ACSR conductors. As a result, ACSR conductors make them widely available in the market. The cost of an ACSR conductor is much less than that of an equivalent copper conductor.
• Proven reliability: Utilities have been using ACSR for many decades. Hence, it has a long service and performance record. Utilities specified it for most EHV lines because of its durability and dependability.

Drawbacks of ACSR Conductor

• High‐temperature sag: Aluminum begins to become soft and annealed above about 93°C. Therefore, above this temperature, pure aluminum starts to anneal. So, this limits the maximum continuous conductor temperature and ampacity. Additionally, at high ambient or loading conditions, an ACSR conductor can sag significantly. For still higher temperature ratings, utilities prefer to use aluminum-conductor steel-supported (ACSS) or all-aluminum alloy AAAC or HTLS conductors instead.
• Steel corrosion risk: The strands of steel core are galvanized. However, sometimes due to improper or damaged zinc coating, corrosion can occur in steel and aluminum. It is especially prevalent in aggressive environments such as polluted or coastal areas. Obviously, the rate of corrosion is higher than expected. Corrosion reduces the strength of steel over time. Therefore, it potentially lowers the lifespan of ACSR.
• Limited current capacity: Because aluminum has only ~60% the conductivity of copper, ACSR must be larger in diameter for the same current. Consequently, the current ratings of ACSR conductors are lower than their equivalent cross-sectioned copper conductors. Thus, ACSR lines may require more parallel circuits to accommodate the growing load demands of the present decade.

Technical Parameters of Commonly Used ACSR

The table below summarizes key properties of three very commonly used ACSR sizes. These sizes are the Panther, Zebra, and Moose. Data include conductor dimensions, mass, DC resistance, current rating (approximate at 65 °C), and tensile (breaking) strength. Values are drawn from IS 398

Video on ACSR Conductors