---
title: "Conductor materials for lines and cables"
subject: "Power System Analysis I"
chapter: 2
key: "semester_4/power_system_analysis_i:conductor-materials-selection"
source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/conductor-materials-selection
site: BCT Engineering
---

# Conductor materials for lines and cables

Power System Analysis I · Chapter 2: Overhead and Underground Transmission

- Asked in: 2069 Poush, 4 marks
- Video: [VR17 31 EEE PTE U1L1 Conductor Materials & types](https://www.youtube.com/watch?v=UZw_yJe_uN8) — EEE VIIT
- 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-materials-selection
- Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-2

## Question

List out the materials used in overhead lines and underground cables. What are the bases for selection of conductors for overhead lines and underground power cables?

## Short answer

Overhead line conductors include ACSR, AAC, hard-drawn copper, and galvanised steel; underground cables use annealed copper or aluminium. Selection bases: high conductivity, tensile strength, low weight, low cost, corrosion resistance, and large diameter to reduce corona for overhead lines; for cables, flexibility and insulation compatibility are also critical.

## Answer

#### Materials used
| Use | Conductor materials |
|---|---|
| Overhead lines | Hard-drawn copper; aluminium (AAC); ACSR (aluminium conductor steel reinforced); all-aluminium alloy (AAAC); galvanised steel (earth wires, short spans); cadmium copper (long spans) |
| Underground cables | Annealed copper; aluminium (stranded, sometimes sector-shaped) |

Cable insulation materials include paper impregnated with oil, PVC, XLPE and rubber. Sheaths are lead or aluminium, and armouring is steel tape or wire.

#### Basis for selecting overhead line conductors
- High conductivity, for low $I^2R$ loss and voltage drop
- High tensile strength, to take wind and ice loads and allow long spans with low sag
- Low weight (density), so that towers are lighter
- Low cost and easy availability
- Resistance to corrosion and weather
- Low coefficient of expansion, so that sag changes little with temperature
- Large diameter for a given resistance, which reduces corona (an advantage of aluminium and ACSR)

#### Basis for selecting cable conductors
- High conductivity, because cable cooling is poor and the conductor must be compact
- Flexibility, for laying and bending (so stranded conductors are used)
- Compatibility with the insulation, and ease of jointing and termination
- Cost: copper gives a smaller size, while aluminium is cheaper and lighter

ACSR is the standard choice for overhead lines. Copper or aluminium with XLPE insulation is common for cables.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why must overhead conductors have high tensile strength?
   A. To reduce corona
   B. To take wind and ice loads and allow long spans with low sag
   C. To reduce cost of insulation
   D. To improve flexibility
   Answer: B. High strength supports loads and allows long spans with small sag. (Key point: Tensile strength)

2. Why are stranded conductors used in cables?
   A. Flexibility for laying and bending
   B. To lower the voltage
   C. To increase corona
   D. To avoid insulation
   Answer: A. Stranding gives flexibility needed for laying and bending. (Key point: Cable conductor)

3. Why must cable conductors have high conductivity?
   A. Cooling is poor and the conductor must be compact
   B. Cables are lighter
   C. Cables carry no current
   D. To reduce armour weight
   Answer: A. Cooling in cables is poor, so low losses and compact size are needed. (Key point: Cable cooling)

## Related in Power System Analysis I

- [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 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
- [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×
- [Locating faults in underground cables](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Acable-fault-location-method) — Power System Analysis I, chapter 2, asked 3×
- [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
- [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

- [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×
- [Conductor selection, 100 MW 80 km, no corona](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aconductor-selection-100mw-80km-corona) — Transmission and Distribution System Design, chapter 4