--- title: "Conductor characteristics, aluminium vs copper" subject: "Transmission and Distribution System Design" chapter: 4 key: "semester_8/transmission_and_distribution_system_design:conductor-characteristics-al-vs-cu" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/conductor-characteristics-al-vs-cu site: BCT Engineering --- # Conductor characteristics, aluminium vs copper Transmission and Distribution System Design · Chapter 4: Conductor and Support Selection - Asked in: 2080 Chaitra, 4 marks - Video: [Why Power Lines Use Aluminum Instead of Copper (Even Though Copper Conducts Better)](https://www.youtube.com/watch?v=Xrx2-xPIo98) — Apex Uncovered - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/conductor-characteristics-al-vs-cu - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-4 ## Question Discuss the essential characteristics of a conductor for an overhead transmission line. Compare the performance of aluminum and copper conductors in this regard. ## Short answer An overhead line conductor should have high electrical conductivity, high tensile strength, low weight, low cost, low thermal expansion, corrosion resistance, and sufficient diameter for corona limitation. Aluminum (as ACSR) is lighter, cheaper, and its larger diameter reduces corona, but has lower tensile strength compensated by steel core; copper has higher conductivity and strength but is heavier and costlier. ## Answer An overhead line conductor should have: 1. High electrical conductivity (low resistivity), for low losses and voltage drop. 2. High tensile strength, to support long spans and wind and ice loads. 3. Low weight per unit length (low density), for less sag and lighter towers. 4. Low cost and easy availability. 5. Low coefficient of thermal expansion, so that sag changes little with temperature. 6. Resistance to corrosion and weather. 7. A large enough diameter to limit corona at high voltage. 8. Easy jointing, and good resistance to fatigue and vibration. #### Aluminium vs copper | Property | Aluminium | Copper | |---|---|---| | Conductivity | About 61% of copper, so 1.6× the area is needed | Highest (reference) | | Density | 2.7 g/cm³, about half the weight for equal resistance | 8.9 g/cm³, heavy | | Tensile strength | Low; reinforced with steel (ACSR) | High | | Diameter for equal resistance | About 1.26× larger, so **less corona** | Smaller | | Thermal expansion | Higher, so more sag change | Lower | | Cost | Cheaper and stable | Costly | | Jointing | Needs special compression joints | Easy | Aluminium (as ACSR or AAAC) is preferred for overhead transmission. It is lighter and cheaper, and its larger diameter reduces corona. The steel core of ACSR makes up for its low strength. Copper is used mainly where space is limited (cables, substations). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. For equal resistance, how does aluminium compare with copper in area and weight? A. Smaller area and heavier B. About 1.6 times the area but about half the weight C. Same area and same weight D. About 1.6 times the area and heavier Answer: B. Aluminium has about 61% of copper's conductivity but lower density (2.7 vs 8.9 g/cm3). (Key point: Equal resistance) 2. Why does aluminium perform better with respect to corona? A. Its larger diameter for equal resistance gives a lower surface gradient B. It has higher conductivity C. It is smoother D. It has higher density Answer: A. About 1.26 times larger diameter reduces corona. (Key point: Corona) 3. Why is a steel core used in ACSR? A. To reduce resistance B. To make up for aluminium's low tensile strength C. To reduce corona D. To lower cost of jointing Answer: B. Aluminium is weak, so steel provides the strength. 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