Conductor Types Used For Overhead Lines

Aluminium and its alloys conductor steel reinforced

The international standards covering most conductor types for overhead lines are IEC 61089 (which supersedes IEC 207, 208, 209 and 210) and EN 50182 and 50183 (see Table 1).

For 36 kV transmission and above both aluminium conductor steel reinforced (ACSR) and all aluminium alloy conductor (AAAC) may be considered. Aluminium conductor alloy reinforced (ACAR) and all aluminium alloy conductors steel reinforced (AACSR) are less common than AAAC and all such conductors may be more expensive than ACSR.

Relevant national and international standards

Historically ACSR has been widely used because of its mechanical strength, the widespread manufacturing capacity and cost effectiveness.

All aluminium conductors (AAC) are also employed at local distribution voltage levels.

From a materials point of view the choice between ACSR and AAAC is not so obvious and at larger conductor sizes the AAAC option becomes more attractive. AAAC can achieve significant strength/weight ratios and for some constructions gives smaller sag and/or lower tower heights. With regard to long-term creep or relaxation, ACSR with its steel core is considerably less likely to be affected.

Jointing does not impose insurmountable difficulties for either ACSR or AAAC types of conductor as long as normal conductor cleaning and general preparation are observed. AAAC is slightly easier to joint than ACSR.

Figure 1 illustrates typical strandings of ACSR. The conductor, with an outer layer of segmented strands, has a smooth surface and a slightly reduced diameter for the same electrical area.

Historically there has been no standard nomenclature for overhead line conductors, although in some parts of the world code names have been used based on animal (ACSR – UK), bird (ACSR – North America), insect (AAAC – UK) or flower (AAAC – North America) names to represent certain conductor types.

Aluminium-based conductors have been referred to by their nominal aluminium area. Thus, ACSR with 54 Al strands surrounding seven steel strands, all strands of diameter d 3.18 mm, was designated 54/7/3.18; alu area 428.9 mm², steel area 55.6 mm² and described as having a nominal aluminium area of 400 mm².

In France, the conductor total area of 485 mm² is quoted and in Germany the aluminium and steel areas, 429/56, are quoted. In Canada and USA, the area is quoted in circular mils (1000 circular mils 0.507 mm²).

Within Europe standard EN50182 has coordinated these codes while permitting each country to retain the actual different conductor types via the National Normative Aspects (NNAs).

Table below explains the EN 50182 designation system.

The development of ‘Gap type’ heat-resistant conductors offers the possibility of higher conductor temperatures.

The design involves an extra high strength galvanized steel core, and heat-resistant aluminium alloy outer layers, separated by a gap filled with heat-resistant grease. To maintain the gap, the wires of the inner layer of the aluminium alloy are trapezoid shaped. Depending on the alloys used, temperatures of up to 210°C are possible, with a current carrying capacity of up to twice that of hard-drawn aluminium.

This offers particular value where projects involve upgrading existing circuits.

Resource: Transmission and Distribution Electrical Engineering by Dr C. R. Bayliss CEng FIET and B. J. Hardy ACGI CEng FIET