--- title: "Reasons for aluminium conductors" subject: "Power System Analysis I" chapter: 2 key: "semester_4/power_system_analysis_i:aluminium-conductors-reasons" source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/aluminium-conductors-reasons site: BCT Engineering --- # Reasons for aluminium conductors Power System Analysis I · Chapter 2: Overhead and Underground Transmission - Asked in: 2068 Bhadra, 4 marks - Video: [WHY ALUMINIUM IS MOSTLY USED IN TRANSMISSION LINE COMPARED TO COPPER](https://www.youtube.com/watch?v=V8I13_F08xk) — Onlineopedia - 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/aluminium-conductors-reasons - Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-2 ## Question Give reasons for extensive use of aluminium conductors in overhead transmission lines. ## Short answer Aluminium is widely used because it is cheaper and lighter than copper, has a larger diameter that reduces corona loss, and offers good conductivity. ACSR adds a steel core for high tensile strength, enabling long spans with low sag, and its oxide layer resists corrosion. ## Answer Aluminium, mostly as ACSR, has replaced copper on overhead lines for the following reasons. - **Lower cost:** Aluminium is much cheaper than copper and more readily available. - **Light weight:** Its density (2.7 g/cm³) is about 30 % of copper's (8.9 g/cm³). For the same resistance, an aluminium conductor weighs about half as much, so towers and insulators can be lighter. - **Larger diameter:** For the same resistance its diameter is about 1.26 times that of copper. This lowers the surface electric stress, so corona loss is reduced, which matters at high voltage. - **Good conductivity:** It has about 60 % of copper's conductivity, which is acceptable when the cross-section is increased. - **Steel reinforcement:** Aluminium alone has low tensile strength. ACSR adds a galvanised steel core, which allows long spans with less sag. - **Corrosion resistance:** A thin oxide layer protects the surface. Its drawbacks are a larger area exposed to wind and ice, a higher coefficient of expansion, and difficult jointing. These are acceptable given its advantages. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why does aluminium's larger diameter help at high voltage? A. It lowers surface electric stress, reducing corona loss B. It raises resistance C. It increases weight D. It improves tensile strength Answer: A. For equal resistance, aluminium is thicker, so surface stress and corona are lower. (Key point: Corona) 2. For the same resistance, an aluminium conductor weighs about what compared with copper? A. Twice as much B. About the same C. About half D. One tenth Answer: C. Its lower density makes it about half the weight, allowing lighter towers. (Key point: Weight) 3. How is aluminium's low tensile strength overcome? A. Using a galvanised steel core (ACSR) B. Adding insulation C. Using thinner strands D. Increasing the voltage Answer: A. ACSR has a steel core that gives strength for long spans with low sag. (Key point: Tensile strength) 4. Aluminium's conductivity relative to copper is about A. 160 % B. 100 % C. 60 % D. 10 % Answer: C. It has about 60 % of copper's conductivity, offset by larger cross-section. (Key point: Conductivity) ## Related in Power System Analysis I - [Requirements of conductors for overhead lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aconductor-requirements) — Power System Analysis I, chapter 2, asked 2× - [Reasons for stranded and bundled conductors](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Areasons-stranded-bundled-conductors) — Power System Analysis I, chapter 2, asked 5× - [Proximity effect in cables vs overhead lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aproximity-effect-cables-vs-lines) — Power System Analysis I, chapter 4 - [Reason for bundling conductors in HV lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Areason-bundling-hv-lines) — Power System Analysis I, chapter 2 - [Underground cables vs overhead lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Acables-vs-overhead-lines) — Power System Analysis I, chapter 2 - [Proximity effect in overhead lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aproximity-effect) — Power System Analysis I, chapter 4 ## Related in other subjects - [Band applications and microwave transmission lines](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aband-applications-transmission-lines) — RF and Microwave Engineering, chapter 1 - [Conductor characteristics, aluminium vs copper](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aconductor-characteristics-al-vs-cu) — Transmission and Distribution System Design, chapter 4 - [Minimum spacing for 30 mm conductors (m = 0.95)](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Acorona-spacing-30mm-0-95) — High Voltage Engineering, chapter 5, asked 4× - [Underground vs overhead distribution systems](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aunderground-vs-overhead-distribution) — Transmission and Distribution System Design, chapter 5, asked 4×