---
title: "Proximity effect in overhead lines"
subject: "Power System Analysis I"
chapter: 4
key: "semester_4/power_system_analysis_i:proximity-effect"
source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/proximity-effect
site: BCT Engineering
---

# Proximity effect in overhead lines

Power System Analysis I · Chapter 4: Line Parameter Calculations

- Asked in: 2071 Bhadra, 5 marks
- Video: [proximity effect | proximity effect in power system | proximity effect in transmission line | hindi](https://www.youtube.com/watch?v=OzVeBZM2L7o) — Mind of Engineer 
- 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/proximity-effect
- Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-4

## Question

What is proximity effect in overhead power transmission? Explain briefly.

## Short answer

Proximity effect is non-uniform current distribution in a conductor due to the magnetic field of a nearby conductor, increasing AC resistance. For opposite currents, current crowds on adjacent faces. It is significant in cables but negligible in overhead lines because of large spacing.

## Answer

**Proximity effect** is the non-uniform distribution of current in a conductor caused by the alternating magnetic field of a nearby current-carrying conductor. It increases the effective AC resistance of the conductor.

#### How it occurs

- The alternating flux of conductor B links parts of conductor A unequally: the side of A nearer to B is linked by more (or less) flux than the far side.
- This produces unequal inductive reactance across the cross-section of A, so current crowds to one side.
- For **opposite currents** (go and return of a circuit), current crowds on the **adjacent (near) faces**; for **currents in the same direction**, it crowds on the **far faces**.

```text
 Opposite currents       Same direction
   [   ##][##   ]        [##   ][   ##]
    A  ->  <- B           A ->    B ->
  (## = higher current density)
```

#### Effects

- The effective current-carrying area is reduced, so **AC resistance rises** and $I^2R$ loss increases.
- It adds to the skin effect; both are included in the AC resistance of a line.

#### Factors

Proximity effect increases with:
- **Frequency** (larger flux variation),
- **Conductor size** (diameter),
- **Closeness of conductors** (smaller spacing),
- Conductivity and permeability of the material.

#### In practice

In **overhead lines** the spacing between phases is several metres, so the proximity effect is negligible. In **underground cables**, conductors are only a few centimetres apart, so the proximity effect is significant and must be considered in the cable's AC resistance.

## Check yourself

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

1. What causes proximity effect?
   A. Alternating magnetic field of a nearby current-carrying conductor distorting current distribution
   B. Corona discharge
   C. Ground capacitance
   D. Temperature rise
   Answer: A. Flux of a nearby conductor links parts of the conductor unequally, causing non-uniform current density. (Key point: Definition)

2. For go and return (opposite) currents in adjacent conductors, where does current crowd?
   A. On the far faces
   B. On the adjacent (near) faces
   C. Uniformly
   D. At the centre
   Answer: B. Opposite currents crowd on adjacent faces; same-direction currents crowd on the far faces. (Key point: Direction dependence)

3. What is the effect on AC resistance?
   A. It decreases
   B. It increases, adding to skin effect, raising I^2R loss
   C. No change
   D. It becomes zero
   Answer: B. The effective current-carrying area is reduced so AC resistance rises. (Key point: Effect)

4. Where is proximity effect significant?
   A. Overhead lines with wide spacing
   B. Underground cables, with conductors only a few cm apart
   C. DC lines
   D. Single conductors
   Answer: B. Overhead spacing is several metres, making it negligible; cables have close spacing. (Key point: Where significant)

## Related in Power System Analysis I

- [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
- [Skin effect in transmission lines](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Askin-effect-brief) — Power System Analysis I, chapter 4
- [Skin effect and proximity effect](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Askin-and-proximity-effect) — Power System Analysis I, chapter 4, asked 3×
- [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×
- [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