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IEC 62219: Formed Wire Concentric Lay Stranded Overhead Conductors
Specifications, Designation System and Testing for Formed Wire Aerial Conductors
Formed Wire Technology and Designation System
IEC 62219 (first edition, 2002) specifies the electrical and mechanical characteristics of concentric-lay overhead conductors made from wires that are formed or shaped before, during, or after stranding. Unlike conventional round-wire conductors covered by IEC 61089, formed wire conductors achieve a significantly higher fill ratio — typically 90-95% compared to 75-80% for round-wire designs — by deforming the constituent wires into trapezoidal, Z-shaped, or sector-shaped cross-sections. This compaction reduces the overall conductor diameter by 10-20% for the same aluminium cross-section, offering substantial benefits in ice and wind loading reduction, corona performance improvement, and increased ampacity within the same right-of-way envelope.
The reduced diameter of formed wire conductors translates directly to lower wind and ice loads on transmission towers, making them an economically attractive option for line uprating and reconductoring projects where existing tower foundations must be reused.
The standard establishes a systematic designation framework. Homogeneous aluminium conductors use the format AxF (e.g., A1F for hard-drawn aluminium, A2F/A3F for aluminium alloys), while composite conductors append a suffix for the core material: AxF/Syz for steel-reinforced types (where y = strength grade 1/2/3, z = zinc coating class A/B) or AxF/SA for aluminium-clad steel reinforcement. A complete designation includes the equivalent aluminium area, core area (when applicable), material codes, and nominal diameter expressed in tenths of a millimetre. For example, 505/65-A1F/S1A-281 identifies a conductor with 505 mm² A1F aluminium, 65 mm² S1A steel core, and 28.1 mm nominal diameter.
| Material Code | Description | Resistivity (nΩ·m) | Conductivity (%IACS) |
|---|---|---|---|
| A1F | Hard-drawn aluminium (IEC 60889) | 28.264 | 61.0 |
| A2F | Al-Mg-Si alloy (IEC 60104) type A2 | 32.530 | 53.0 |
| A3F | Al-Mg-Si alloy (IEC 60104) type A3 | 32.840 | 52.5 |
| S1A/S1B | Regular strength zinc-coated steel | — | — |
| S2A/S2B | High strength zinc-coated steel | — | — |
| S3A | Extra high strength zinc-coated steel | — | — |
| SA | Aluminium-clad steel | — | — |
Three production processes are recognised. The first pre-forms wires then strands them; the second combines forming and stranding in a single operation; and the third strands round wires first then compacts the layer to a circular cross-section before adding further layers. Each approach affects the wire’s mechanical properties differently — wires formed before stranding must have their characteristics verified based on equivalent round-wire diameter calculations, while wires formed during stranding are tested as round wires prior to the forming operation. This distinction has important implications for quality control and acceptance testing. Manufacturers must clearly document which process is used, as it directly affects the expected modulus, fill ratio, and surface finish of the final product.
When replacing existing round-wire ACSR conductors with formed wire equivalents, pay careful attention to the steel ratio and overall stiffness. Formed wire conductors typically have higher modulus of elasticity and different creep characteristics, which can affect sag-tension calculations and clamp selection.
Mechanical and Electrical Testing Requirements
IEC 62219 classifies tests into type tests (performed once for a new conductor design), sample tests (on each manufacturing lot), and routine checks. Type tests include the critical stress-strain test (Annex B), which establishes the conductor’s elastic and plastic deformation behaviour under incremental tensile loading. The test procedure requires a minimum sample length of 400 times the nominal diameter, pre-conditioning at 20 °C ± 5 °C, and load application in prescribed increments up to 50% of the rated tensile strength (RTS), followed by unloading and reloading cycles. The resulting stress-strain curves are essential for accurate sag-tension calculations in line design. Additionally, the Young’s modulus determined from the stress-strain test is used in the design of tower loadings and vibration dampers, making it one of the most important mechanical parameters for transmission line engineers.
Do not overlook the grease mass requirements in Annex C. Formed wire conductors often require inter-strand grease filling for corrosion protection, especially in coastal or industrial environments. The nominal grease mass is specified as a function of conductor diameter and construction type; deviations affect both corrosion performance and conductor mass per unit length.
Sample tests verify lay length and lay ratio (Clause 5.5.3), which must fall within prescribed ranges: for a 6-wire steel core layer the lay ratio must be between 16 and 26; for 12-wire layers between 14 and 22; with special constructions (Figure 1b designs) permitting ratios as low as 10. The outer layer must be right-hand lay unless otherwise specified. Tensile strength testing on completed conductors ensures that the rated breaking load meets design values, while linear density (mass per unit length) verification accounts for both metallic mass and grease contribution. Conductor surface finish must be free from visible imperfections such as nicks, tears, or die marks that would impair commercial quality.
| Test | Clause | Requirement |
|---|---|---|
| Stress-strain test | Annex B | Sample length ≥ 400 × diameter; plot modulus and permanent elongation |
| Lay ratio (6-wire core layer) | 5.5.3a | 16 to 26 |
| Lay ratio (12-wire core layer) | 5.5.3b | 14 to 22 |
| Conductor diameter tolerance | 5.3 | Per Annex D tables ± tolerances |
| Rated tensile strength | 5.8 | ≥ specified value per design |
| Grease mass | Annex C | Per table as function of diameter |
For engineering design offices: when performing sag-tension calculations for formed wire conductors, use the stress-strain data from the actual type test report rather than generic material properties. The forming process work-hardens the aluminium, resulting in a 5-10% higher modulus than round-wire equivalents, which affects final sag under high-temperature operation.
When specifying formed wire conductors for new transmission lines or reconductoring projects, the selection of appropriate corrosion protection measures is critical for service life. The standard allows for grease-filled or greaseless constructions depending on environmental conditions. In coastal or industrial environments, the inter-strand spaces should be completely filled with corrosion-inhibiting grease meeting the mass requirements of Annex C. For dry inland environments, greaseless constructions may be acceptable, offering reduced weight and lower installation cost. The purchaser should always specify the environmental conditions at the time of ordering so that the manufacturer can recommend the appropriate corrosion protection strategy.
Frequently Asked Questions
Q1: What are the main advantages of formed wire conductors over conventional round-wire ACSR?
Formed wire conductors achieve 10-20% diameter reduction for equivalent aluminium area, reducing wind and ice loads by 15-25%. The smoother surface also reduces corona discharge and radio interference voltage (RIV) levels, especially beneficial at transmission voltages above 345 kV.
Formed wire conductors achieve 10-20% diameter reduction for equivalent aluminium area, reducing wind and ice loads by 15-25%. The smoother surface also reduces corona discharge and radio interference voltage (RIV) levels, especially beneficial at transmission voltages above 345 kV.
Q2: Can formed wire conductors be spliced using standard compression fittings?
Yes, but the fittings must be specifically designed for the non-circular wire profiles. Standard round-wire fittings may not achieve adequate compression on trapezoidal wires. Most manufacturers provide dedicated fitting kits validated through full-tension splice testing per the standard’s requirements.
Yes, but the fittings must be specifically designed for the non-circular wire profiles. Standard round-wire fittings may not achieve adequate compression on trapezoidal wires. Most manufacturers provide dedicated fitting kits validated through full-tension splice testing per the standard’s requirements.
Q3: How does the A1F/A2F/A3F designation relate to conductor ampacity?
A1F (61% IACS) offers the highest conductivity. A2F (53% IACS) and A3F (52.5% IACS) are aluminium alloy conductors with higher strength-to-weight ratios but lower conductivity. The choice depends on whether the line is limited by thermal rating (choose A1F) or by sag/clearance constraints (choose A2F or A3F for higher strength at elevated temperature).
A1F (61% IACS) offers the highest conductivity. A2F (53% IACS) and A3F (52.5% IACS) are aluminium alloy conductors with higher strength-to-weight ratios but lower conductivity. The choice depends on whether the line is limited by thermal rating (choose A1F) or by sag/clearance constraints (choose A2F or A3F for higher strength at elevated temperature).
Q4: Is the IEC 62219 conductor designation compatible with existing ACSR naming conventions?
Partially. While the standard aims to cross-reference with established designs in Annex D, the designation system differs from traditional “ACSR 26/7” or “Dove/Condor” naming. Engineers should maintain a cross-reference table during specification to avoid ordering errors.
Partially. While the standard aims to cross-reference with established designs in Annex D, the designation system differs from traditional “ACSR 26/7” or “Dove/Condor” naming. Engineers should maintain a cross-reference table during specification to avoid ordering errors.
