ACSR conductor means Aluminum Conductor with Steel Reinforce. ACSR is the most standard choice for high‐voltage overhead transmission lines. An ACSR consists of mainly two parts. It has multiple layers of pure aluminum strands for carrying current. It also has a central core of galvanized steel to provide tensile strength to the conductor. The aluminum strands are formed by hard drawn process. Aluminum is used here for its good conductivity and low weight. This composite design combines aluminum’s high conductivity and light weight with steel’s strength, allowing higher tension.
Basic Construction of ACSR Conductors
ACSR conductors are made by stranding concentric layers of wire. The strands of the central steel core are galvanized high-carbon steel wires. Around this core one or more layers of aluminum wires are laid helically. The aluminum strands carry almost all the current, while the steel core carries the mechanical load. The electrical conductivity of steel is negligible compared to aluminum. The each steel strand is zinc‐galvanized to prevent galvanic corrosion of aluminum.
Applications of ACSR Conductors
ACSR conductors serve medium‐through‐extra‐high voltage lines across India. They are used on 132 kV, 220 kV and 400 kV transmission lines and even lower‐voltage distribution lines, due to their robustness. As per general practice, 132 kV transmission lines use ACSR Panther conductor, 220 kV lines often use ACSR Zebra, Wolf or Goat variants and 400 kV lines are built with ACSR Moose. ACSR is favored for long river crossings and rugged terrain because of its high strength‐to‐weight ratio. Sometimes for long river crossing or similar purposes special type ACSR conductors are required. Also, for AIS strung buses, dropper connections, and jumper connections ACSR conductors are widely used in substations.
Advantages of ACSR
- High tensile strength: The steel core gives very high mechanical strength, allowing long spans and high tensions. The mechanical strength of ACSR is far better than that of all‐aluminum conductors.
- Good conductivity and light weight: Aluminum used for strands is normally 99.5% pure. It provides excellent conductivity. Although aluminum has lower conductivity than copper but its wight per unit volume is only ~30% of copper. This yields high ampacity per weight for aluminum made conductors. The combination of light weight and high conductivity with the mechanical strength of steel permits higher tensions and significantly less sag than all-aluminum conductors.
- Cost-effectiveness and availability: Aluminum and steel both are relatively inexpensive and abundant compared to copper. ACSR is produced by many manufacturers, making it widely available in the market. The Panther, Zebra, and Moose variants are most commonly used for high voltage transmission purposes. The cost of an ACSR made transmission line is much less per kA than an equivalent copper line.
- Proven reliability: Utilities are using ACSR from many decades hence it has long service and performance record. It is specified by utilities for most EHV lines because of its durability and dependability.
Drawbacks of ACSR
- High‐temperature sag: Aluminum begins to soften and anneal above about 75 °C. This limits the maximum continuous conductor temperature and ampacity. At high ambient or loading conditions, ACSR 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 but sometimes due to improper or damaged zinc coating corrosion takes place in steel and aluminium. Specially in aggressive environments of polluted or coastal areas, the rate of corrosion is higher than expected. Corrosion reduces the steel strength over years, potentially lowering 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. Current ratings of ACSR conductors are lower than their equivalent sized HTLS conductors. Thus ACSR lines may require more parallel circuits accommodate the growing load demands 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
| Parameter | Panther | Zebra | Moose |
|---|---|---|---|
| Standard | IS 398 Part II | ||
| Voltage Level | 132 kV | 220 kV | 400 kV |
| Stranding (Al/St) | 30/7 | 54/7 | 54/7 |
| Overall Diameter (mm) | 21.00 | 28.62 | 31.77 |
| Aluminum Area (mm²) | 300 | 484 | 528 |
| Steel Area (mm²) | 70 | 60 | 60 |
| Total Cross-sectional Area (mm²) | 370 | 544 | 588 |
| Approximate Weight (kg/km) | 1222 | 1817 | 1994 |
| Breaking Load (kgf) | 9640 | 13400 | 14000 |
| DC Resistance at 20°C (ohm/km) | 0.0991 | 0.0598 | 0.0551 |
| Current Carrying Capacity (A) | 665 | 895 | 945 |