--- title: "Requirements of conductors for overhead lines" subject: "Power System Analysis I" chapter: 2 key: "semester_4/power_system_analysis_i:conductor-requirements" source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/conductor-requirements site: BCT Engineering --- # Requirements of conductors for overhead lines Power System Analysis I · Chapter 2: Overhead and Underground Transmission - Asked in: 2070 Bhadra, 4 marks; 2068 Magh, 4 marks (asked 2 times) - Video: [Conductor Materials for Overhead Transmission Line||Power Systems-II||Lecture-1](https://www.youtube.com/watch?v=RFAUf2tOsDw) — Bhaskar Kandula - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/conductor-requirements - Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-2 ## Question Mention the main requirements of conductors for overhead transmission lines. ## Short answer Conductors need high electrical conductivity, high tensile strength, low specific gravity, low cost, flexibility, corrosion resistance, low thermal expansion, high melting point, and resistance to fatigue. ACSR (aluminium conductor steel-reinforced) best meets these requirements. ## Answer A conductor for an overhead line should carry current efficiently and safely for many years under mechanical and weather loads. Its main requirements are: 1. **High electrical conductivity** (low resistivity) to reduce $I^2R$ loss and voltage drop. 2. **High tensile strength** to withstand its own weight, wind and ice loading and allow long spans with less sag. 3. **Low specific gravity (light weight)** so that towers can be lighter and sag is smaller. 4. **Low cost** and easy availability so the line is economical. 5. **Flexibility:** easy to handle, string and wind on drums (achieved by stranding). 6. **Durability and corrosion resistance** against weather and pollution. 7. **Low coefficient of thermal expansion** so that sag does not change much with temperature. 8. **High melting point / ability to work hot** to carry overloads and short-circuit currents. 9. **Larger diameter** (for EHV) to reduce corona. 10. **Not brittle;** should resist fatigue from vibration. | Material | Comment | |---|---| | Copper | Best conductivity, costly, heavy | | Aluminium | Light and cheap, lower strength | | ACSR | Aluminium for current, steel core for strength; most used (e.g. ACSR Dog, Bear, Moose in Nepal) | | AAAC | Aluminium alloy, good strength, corrosion-resistant | | Galvanised steel | Very strong, poor conductivity; used for earth wires and long river crossings | ACSR meets most of these requirements and is widely used in Nepal's transmission and distribution lines. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why must an overhead line conductor have high electrical conductivity? A. To increase the tensile strength B. To reduce the weight on towers C. To reduce I^2R loss and voltage drop D. To raise the melting point Answer: C. Low resistivity means less resistance, hence smaller I^2R loss and voltage drop. (Key point: Why high conductivity) 2. What is the benefit of a light conductor (low specific gravity)? A. Higher corona inception voltage B. Higher conductivity C. Better corrosion resistance D. Lighter towers and smaller sag Answer: D. Less weight means lower mechanical loading on towers and smaller sag. (Key point: Role of low specific gravity) 3. In ACSR, what are the roles of aluminium and steel? A. Steel carries the current, aluminium gives strength B. Aluminium carries the current, steel core gives strength C. Both carry current equally D. Steel reduces corona, aluminium gives flexibility Answer: B. ACSR combines the conductivity of aluminium with the tensile strength of a steel core. (Key point: ACSR construction) 4. Why are overhead conductors made of stranded wires? A. To raise conductivity above solid wire B. To eliminate corona completely C. To lower the cost of the aluminium D. For flexibility, easy handling and winding on drums Answer: D. Stranding gives flexibility so the conductor can be handled, strung and wound on drums. 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