---
title: "Short note: Eddy current loss"
subject: "Electrical Machine"
chapter: 1
key: "semester_4/electrical_machine:short-note-eddy-current-loss"
source: https://www.bctengineer.com/q/semester_4/electrical_machine/short-note-eddy-current-loss
site: BCT Engineering
---

# Short note: Eddy current loss

Electrical Machine · Chapter 1: Magnetic Circuits and Induction

- Asked in: 2068 Magh, 4 marks
- Video: [Eddy current & Eddy Current loss | Electrical Engineering](https://www.youtube.com/watch?v=XPk38Tz_UC0) — Gaurav J - TheElectricalGuy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/electrical_machine/short-note-eddy-current-loss
- Whole chapter: https://www.bctengineer.com/md/semester_4/electrical_machine/chapter-1

## Question

Write a short note on eddy current loss.

## Short answer

Eddy current loss is heat generated in a magnetic core by circulating currents induced by alternating flux. P_e = k_e B_max² f² t² V. It is minimized by using thin laminated sheets insulated from each other and high-resistivity silicon steel.

## Answer

**Eddy current loss** is the power wasted as heat in a magnetic core (or any conducting mass) because of circulating currents induced in it by a changing flux.

**Cause:** by Faraday's law, an alternating flux induces an emf not only in the windings but also in the iron core. As the core is a conductor, this emf drives small closed currents, called eddy currents, in planes at right angles to the flux. They cause I²R loss.

**Expression:** for a lamination of thickness *t*, 

Pₑ = kₑ B_max² f² t² V  watts

where kₑ depends on the resistivity of the material, B_max is the maximum flux density, *f* the frequency and *V* the volume.

**Effects**
- Heating of the core, which lowers the efficiency.
- Needs extra cooling and reduces the rating.

**Methods of reduction**
1. Build the core from thin laminated sheets (0.35–0.5 mm).
2. Insulate the laminations from one another with varnish or oxide layers, so that the eddy path is cut into small loops.
3. Use silicon steel, whose higher resistivity limits the currents.
4. Use ferrite or iron-dust cores for high frequency.

**Uses:** the same effect is useful in induction furnaces, eddy-current brakes and induction heating.

## Check yourself

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

1. What causes eddy currents in a core?
   A. The emf induced in the conducting core itself by the alternating flux
   B. Current in the winding insulation
   C. Friction of domains
   D. Air gap leakage
   Answer: A. Alternating flux induces an emf in the core, which drives circulating currents in planes perpendicular to the flux. (Key point: Cause)

2. On what does eddy loss depend according to Pe = ke Bmax^2 f^2 t^2 V?
   A. Thickness squared and frequency squared
   B. Only the volume
   C. Frequency to power 1.6
   D. Thickness and frequency linearly
   Answer: A. Pe is proportional to f^2 and t^2. (Key point: Expression)

3. Why are laminations insulated from each other?
   A. To cut the eddy path into small loops, limiting the currents
   B. To reduce hysteresis loss
   C. To raise the flux
   D. To lower core permeability
   Answer: A. Insulation breaks up the conducting path so eddy currents are confined to thin sheets. (Key point: Insulated laminations)

4. Where is the eddy current effect put to use?
   A. Permanent magnets
   B. Capacitors
   C. Transformer cores
   D. Induction furnaces and eddy-current brakes
   Answer: D. Induction heating, furnaces and eddy-current brakes use the effect. (Key point: Useful applications)

## Related in Electrical Machine

- [Eddy current loss and its minimization](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Aeddy-current-loss-minimize) — Electrical Machines I, chapter 1
- [Short note: Eddy current loss](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Anote-eddy-current-loss) — Electrical Machines, chapter 1
- [Hysteresis and eddy current losses; loop area](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machine%3Ahysteresis-eddy-loss-area) — Electrical Machine, chapter 1
- [Hysteresis and eddy current losses, reduction](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Ahysteresis-eddy-losses-reduce) — Electrical Machines, chapter 1
- [No-load current components, iron loss and core flux](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ano-load-current-10a-0p3pf-500turns) — Electrical Machines I, chapter 2
- [Full-load torque, rotor current and copper loss of 440 V motor](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Aim-440v-1425rpm-rotor-impedance) — Electrical Machines I, chapter 5

## Related in other subjects

- [Hysteresis loss and eddy current loss](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Ahysteresis-eddy-loss) — Electric Machine Design, chapter 1