---
title: "T/F: corona dominating for LV lines"
subject: "Transmission and Distribution System Design"
chapter: 4
key: "semester_8/transmission_and_distribution_system_design:tf-corona-lv-lines"
source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-corona-lv-lines
site: BCT Engineering
---

# T/F: corona dominating for LV lines

Transmission and Distribution System Design · Chapter 4: Conductor and Support Selection

- Asked in: 2077 Chaitra, 4 marks; 2073 Bhadra, 4 marks (asked 2 times)
- 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/tf-corona-lv-lines
- Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-4

## Question

State and justify whether the following statement is TRUE or FALSE: Corona is more dominating design criterion for LV transmission lines.

## Short answer

FALSE. Corona inception voltage is far above LV line voltages, so corona is negligible. It becomes a design constraint only for EHV/UHV lines (≥220 kV), while LV lines are governed by voltage drop and thermal limits.

## Answer

**FALSE.**

Corona starts when the phase voltage exceeds the disruptive critical voltage

$$
V_d = 21.1\,m_0\,\delta\,r\ln\frac{D}{r}\ \text{kV}
$$

- On LV and MV lines (up to 33 kV), the operating voltage is far below $V_d$ even for small conductors. For example, a 10 mm conductor at 1 m spacing has $V_d \approx 21.1 \times 0.85 \times 0.5\ln(200) \approx 47.5$ kV per phase, which is well above 33 kV/$\sqrt{3}$. So corona is practically absent.
- Corona becomes a governing design criterion only for **EHV/UHV lines (220 kV and above)**. There it sets:
  - the minimum conductor diameter,
  - the use of bundled conductors (400 kV and above),
  - limits on radio interference and audible noise.

LV line design is governed instead by voltage drop, current-carrying capacity and mechanical strength.

## Check yourself

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

1. Corona is more dominating as a design criterion for LV lines. This is:
   A. True
   B. False, it dominates only for EHV/UHV lines
   C. True for lines below 11 kV
   D. False, it dominates for all voltages equally
   Answer: B. At low voltages the operating voltage is far below the critical voltage. (Key point: Verdict)

2. Why is corona practically absent on lines up to 33 kV?
   A. Operating phase voltage is well below the disruptive critical voltage Vd
   B. Air is a better insulator at low voltage
   C. Conductors are insulated
   D. Spacing is very large
   Answer: A. Even small conductors give Vd above the phase voltage of such lines. (Key point: Why absent)

3. What governs LV line design instead of corona?
   A. Radio interference
   B. Voltage drop, current-carrying capacity and mechanical strength
   C. Audible noise
   D. Bundle design
   Answer: B. These are the dominant criteria at low voltage. (Key point: What governs LV)

## Related in Transmission and Distribution System Design

- [Justify higher voltage/more circuits for more power](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Ajustify-higher-voltage-more-circuits) — Transmission and Distribution System Design, chapter 2
- [T/F: larger conductor raises corona inception voltage](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-conductor-size-corona-inception) — Transmission and Distribution System Design, chapter 4, asked 2×
- [T/F: corona inception voltage and GMR](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-corona-inception-gmr) — Transmission and Distribution System Design, chapter 4
- [T/F: stability criterion implies thermal criterion](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-stability-implies-thermal) — Transmission and Distribution System Design, chapter 4, asked 2×
- [T/F: radial more reliable than network](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-radial-more-reliable-network) — Transmission and Distribution System Design, chapter 5, asked 2×
- [T/F: grid connected system more stable](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-grid-connected-more-stable) — Transmission and Distribution System Design, chapter 1

## Related in other subjects

- [True/False: ampere conductors and temperature rise](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atf-ampere-conductor-temperature) — Electric Machine Design, chapter 5
- [True/False: armature reaction and ampere conductors](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atf-armature-reaction-ampere-conductor) — Electric Machine Design, chapter 5
- [True/False: air gap length and cost](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atf-air-gap-cost) — Electric Machine Design, chapter 5
- [True/False: magnetic loading and teeth flux density](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atf-magnetic-loading-teeth) — Electric Machine Design, chapter 5