In the vast power industry, overhead conductors serve as the vital arteries that deliver energy from power plants to consumers. Correctly selecting these conductors is far more than a simple equipment purchase; it is a strategic engineering decision that directly affects network stability, project economic efficiency, and public safety. Choosing the wrong conductor type or size can have severe consequences: from unacceptable voltage drop and high energy losses to mechanical hazards such as conductor breakage under severe weather conditions. In this specialist article from Sim Rad Sama’s industrial magazine, we draw on up‑to‑date engineering knowledge to analyse the key parameters for selecting the optimum overhead conductor.
Step One: Recognising and Selecting the Conductor Type
Before entering sizing calculations, we must determine which conductor construction suits the climate and mechanical requirements of our project. In Iran, two main categories of bare conductors are most widely used:
1. Aluminium Conductor Steel‑Reinforced (ACSR)
The ACSR conductor, known in the industry as aluminium conductor with a steel core, is the backbone of transmission and sub‑transmission lines.
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Engineering construction: The conductor consists of a central steel core (responsible for bearing mechanical tension) and outer aluminium layers (responsible for electrical conduction).
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Specialist core types: Depending on environmental conditions (such as the level of corrosiveness), the type of coating on the steel core becomes important:
a) ACSR/GA: Steel core with a galvanised (zinc) coating, the most common and economical type.
b) ACSR/AW: Steel core with a thick aluminium cladding, offering much higher corrosion resistance and ideal for coastal and humid regions. -
Why ACSR? The unique combination of “acceptable electrical conductivity of aluminium” and “high tensile strength of steel” allows its use over long spans.
2. All Aluminium Alloy Conductor (AAAC)
In contrast to ACSR, AAAC conductors are made entirely of high‑strength aluminium alloy strands.
Analysing the difference between ACSR and AAAC:
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Weight: Because AAAC has no steel core, it is lighter, which reduces the dead load on towers.
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Corrosion: AAAC’s resistance to environmental corrosion is better than that of standard ACSR.
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Mechanical strength: Although modern alloys are strong, for similar sizes the ultimate tensile strength of ACSR (thanks to the steel) is usually higher.
Step Two: Trade Names and Commonly Used Sizes
One of the frequent questions from engineers concerns the animal names used for different conductor sizes. In the British Standard (BS), an animal name is assigned to each size to facilitate ordering. Below you will find the best‑selling products of Sim Rad Sama:
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Mink: Cross‑sectional area 73.6 mm² | Construction: 6 aluminium strands, 1 steel strand | Application: Rural medium‑voltage distribution lines
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Hyena: Cross‑sectional area 126 mm² | Construction: 7 aluminium strands, 7 steel strands | Application: Windy areas and medium spans
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Dog: Cross‑sectional area 118 mm² | Construction: 6 aluminium strands, 7 steel strands | Application: Sub‑transmission and light transmission lines
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Wolf: Cross‑sectional area 158 mm² | Construction: 30 aluminium strands, 7 steel strands | Application: Main and heavily loaded transmission lines
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Lynx: Cross‑sectional area 226 mm² | Construction: 30 aluminium strands, 7 steel strands | Application: High‑voltage and heavy‑duty transmission lines
Step Three: Determining the Conductor Cross‑Section and Size
After selecting the conductor type, we come to the most critical stage: sizing. This process is a precise balance between electrical and mechanical factors.
(a) Electrical Considerations
Objective: Transmit the required power with minimum losses while meeting standards.
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Current‑carrying capacity (ampacity) and the load current: The most fundamental criterion is the maximum expected line current over the planning horizon. The conductor size must be chosen so that under the worst ambient temperature conditions (e.g. a summer afternoon), the conductor temperature does not exceed the permissible standard limit (e.g. 75 °C), thereby preventing damage to the wire structure.
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Electrical resistance and power losses: Every conductor has ohmic resistance. The electrical resistance of an ACSR or alloy conductor directly causes energy loss in the form of heat. Economic note: Sometimes selecting a size larger than the minimum required by current, by reducing resistance and losses, recoups the extra initial cost within the first few years of operation.
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Voltage drop: On long distribution lines (especially rural feeders), even if the conductor size is adequate for the load current, the voltage drop at the end of the line may exceed the permissible limit (typically 5%). In such cases, the conductor size is increased not for current reasons but to control voltage drop.
(b) Mechanical and Environmental Considerations
Objective: Ensure the physical stability of the line under imposed forces.
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Span length and tension: The distance between two towers (span) determines the tension force applied to the wire. For long spans and valley crossings, particular attention must be paid to the conductor’s breaking strength specification.
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Weather conditions: The design must consider the worst‑case weather scenario for the area. Strong winds (horizontal force) and ice accretion on the wire (additional vertical load) significantly increase mechanical stresses, which the selected conductor must be capable of withstanding.
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Sag (conductor catenary): The choice of size and the initial tension setting must be such that the sag of the wire on the hottest day of the year, or under the heaviest ice load, does not violate the vertical safety clearance to the ground or obstacles below.
Step Four: Installation Requirements and Safety Standards
In addition to meticulous choice of conductor type and size, the standard installation and stringing process in overhead networks plays a decisive role in the service life and stability of transmission lines. When erecting ACSR and all‑aluminium conductors, contractors must use standard gripping equipment and sheaves to prevent any scratching, crushing or mechanical damage to the outer aluminium strands of the conductor.
Damage to the conductor surface not only reduces its mechanical strength but, on high‑voltage lines, also intensifies the corona phenomenon, generates radio noise, increases power losses and accelerates corrosion in humid environments.
Furthermore, the precise adjustment of sag and tension must be carried out strictly in accordance with the cable engineering tables, the exact span length and the exact ambient temperature at the time of installation. Excessive tension can lead to conductor breakage or tower damage during severe winter cold, while too little tension results in impermissible sag in summer heat and associated life‑threatening hazards. To maintain network integrity, it is recommended always to use hardware and clamps that are fully matched to the size, construction and material of the manufactured conductors, so that electrical and mechanical connections remain at the highest level of safety.
Frequently Asked Questions
1. What is the main difference between ACSR/GA and ACSR/AW?
In the GA type, the steel core is coated with zinc (galvanised), whereas in the AW type the steel core is clad with a thick layer of aluminium. The AW type offers far higher resistance to rust and slightly better electrical conductivity, but it also has a higher price.
2. Which conductor is more suitable for the coastal areas of northern or southern Iran?
For regions with high humidity and salinity, the use of ACSR/AW or All Aluminium Alloy (AAAC) conductors is recommended, because sea salt causes rapid corrosion of ordinary galvanised steel cores.
3. Can standard current rating tables be used for all projects?
No. Standard tables are usually compiled for an ambient temperature of 25 °C or 40 °C and at sea level. For projects in very hot or high‑altitude areas, correction factors must be applied to the current‑carrying capacity. Sim Rad Sama’s technical specialists can assist you with these calculations.
Sim Rad Sama’s Role in Your Project
Selecting an overhead conductor is a complex process dependent on numerous variables. Sim Rad Sama Company, as one of the pioneers of the industry and a manufacturer of ACSR conductors in Iran, is not merely a supplier; we are your technical partner. Utilising cutting‑edge technology, we produce a variety of overhead conductors including ACSR (with diverse GA and AW cores) and alloy conductors to the highest quality standards.
Our services for engineers and contractors:
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Provision of precise and complete conductor technical data for use in design software.
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Consultation on selecting the optimum conductor type based on the climatic conditions of your project.
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Supply of a wide range of standard sizes.
For specialist advice, an up‑to‑date price enquiry, and to receive our comprehensive product catalogue, please contact the Sim Rad Sama Engineering Sales Department.