---
title: "Why LV winding is placed near core"
subject: "Electric Machine Design"
chapter: 3
key: "semester_5/electric_machine_design:lv-winding-near-core"
source: https://www.bctengineer.com/q/semester_5/electric_machine_design/lv-winding-near-core
site: BCT Engineering
---

# Why LV winding is placed near core

Electric Machine Design · Chapter 3: Transformer Design

- Asked in: 2078 Bhadra, 4 marks
- Video: [Why low voltage winding is placed near the core? Why not high voltage winding In Hindi](https://www.youtube.com/watch?v=j3htKpdEOO8) — CS Electrical And Electronics
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/electric_machine_design/lv-winding-near-core
- Whole chapter: https://www.bctengineer.com/md/semester_5/electric_machine_design/chapter-3

## Question

Why is the low voltage winding of transformer placed near to the core in core type transformer?

## Short answer

LV is placed near the core because the core is earthed, so only thin insulation is needed; this keeps winding diameters small, reducing copper weight, loss, and leakage reactance. It also leaves the HV winding outside for easy tapping and repair.

## Answer

In a core type transformer the LV winding is placed next to the core, and the HV winding is wound concentrically over it, mainly to save insulation.

```text
  core | thin ins | LV | duct | HV
```

#### Reasons
1. **Insulation:** the core is earthed. The insulation needed between a winding and the core depends on the winding voltage. LV next to the core needs only thin insulation. If HV were next to the core, a thick insulation barrier for the full HV would be needed there as well as between the windings.
2. **Smaller size and cost:** less insulation near the core keeps the winding diameters small. Mean length of turn, copper weight, $I^2R$ loss and cost are reduced.
3. **Lower leakage reactance:** a smaller radial gap between core and windings means less leakage flux.
4. **Tappings and maintenance:** tappings for voltage control are put on the HV winding (it carries less current). With HV outside, tappings are easy to bring out and the winding is easy to reach for repair.

So the order core → LV → HV gives the most economical and practical design.

## Check yourself

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

1. The core is at earth potential. Placing LV next to it requires:
   A. Thick insulation for full HV
   B. Only thin insulation
   C. No insulation
   D. A metal screen
   Answer: B. Insulation depends on winding voltage. (Key point: Core potential)

2. How does LV near the core reduce cost?
   A. It lowers core loss
   B. It removes the need for oil
   C. It increases the window
   D. Smaller winding diameters give shorter mean turn and less copper
   Answer: D. Less insulation near the core means smaller diameters, shorter turns, lower I^2R loss. (Key point: Size and cost)

3. Why is it convenient to have HV outside?
   A. HV is lighter
   B. Tappings are taken from HV and are easy to access and repair
   C. Core cools better
   D. It increases leakage
   Answer: B. Tappings are on the low-current HV winding. (Key point: Tappings)

## Related in Electric Machine Design

- [Reasons: distribution efficiency and LV placement](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adistribution-efficiency-lv-placement) — Electric Machine Design, chapter 3
- [Design: 100 kVA 11/132 kV transformer with winding data](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adesign-100kva-11-132kv) — Electric Machine Design, chapter 3, asked 3×
- [Core type versus shell type transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Acore-vs-shell-transformer) — Electric Machine Design, chapter 3, asked 3×
- [Leakage reactance of core type transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Aleakage-reactance-core-type) — Electric Machine Design, chapter 3, asked 3×
- [Requirements of transformer core material](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Atransformer-core-material-requirements) — Electric Machine Design, chapter 1
- [Per unit resistance drop of core type transformer](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Aper-unit-resistance-drop) — Electric Machine Design, chapter 3

## Related in other subjects

- [Reluctances and air gap flux of two-winding core](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Atwo-winding-core-reluctance-airgap-flux) — Electrical Machines I, chapter 1
- [LV voltage of Δ–Y bank of 100 kVA transformers](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Adelta-star-bank-100kva-lv-voltage) — Electrical Machines I, chapter 2
- [Static differential relay for two-winding transformer](https://www.bctengineer.com/question.md?key=semester_6%2Fswitchgear_and_protection%3Astatic-differential-two-winding) — Switchgear and Protection, chapter 8
- [Transformer no-load and load operation, constant core flux](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Aideal-transformer-noload-load-constant-flux) — Electrical Machines I, chapter 2, asked 5×