---
title: "True/False: armature reaction and ampere conductors"
subject: "Electric Machine Design"
chapter: 5
key: "semester_5/electric_machine_design:tf-armature-reaction-ampere-conductor"
source: https://www.bctengineer.com/q/semester_5/electric_machine_design/tf-armature-reaction-ampere-conductor
site: BCT Engineering
---

# True/False: armature reaction and ampere conductors

Electric Machine Design · Chapter 5: DC Machine Design

- Asked in: 2069 Asar, 1+3 marks
- Video: [Demystifying Armature Reaction: Interpoles & Compensating Windings Revealed!](https://www.youtube.com/watch?v=5SzqQ8klzmI) — Electrology
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/electric_machine_design/tf-armature-reaction-ampere-conductor
- Whole chapter: https://www.bctengineer.com/md/semester_5/electric_machine_design/chapter-5

## Question

State and justify whether the following statement is TRUE or FALSE: Armature reaction in DC machine is depended on large value of ampere conductor.

## Short answer

TRUE. Armature mmf per pole is directly proportional to ampere conductors per metre, so a larger ac causes stronger armature reaction and flux distortion.

## Answer

**TRUE.**

The armature mmf per pole is
$$
AT_a = \frac{I_zZ}{2P} = \frac{ac\,\pi D}{2P}
$$
So, for a given diameter and number of poles, armature mmf is directly proportional to the specific electric loading $ac$. A large $ac$ produces strong armature reaction: more cross-magnetisation, more distortion of the gap flux, more demagnetising effect at saturation, and poorer commutation. A larger field mmf (or compensating winding) is then needed.

**Example:** with $ac = 22000$ A/m, $D = 0.306$ m and $P = 4$, $AT_a = 22000 \times \pi \times 0.306/8 \approx 2640$ A per pole; doubling $ac$ doubles this armature mmf. Hence designers limit $ac$, or add interpoles and compensating windings in heavily loaded machines.

## Check yourself

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

1. Armature reaction depends on large ampere conductor. Which is correct?
   A. False: independent of ac
   B. False: depends only on flux
   C. True: but only at no load
   D. True: armature mmf is proportional to ac
   Answer: D. AT = ac pi D/2P. (Key point: True or false)

2. What does strong armature reaction cause?
   A. Flux distortion, demagnetising effect, poorer commutation
   B. Lower copper loss
   C. Higher efficiency
   D. Reduced field requirement
   Answer: A. More field mmf or compensating winding is needed. (Key point: Effects)

3. With ac = 22000, D = 0.306 m, P = 4, AT per pole is about
   A. 5280 A
   B. 1320 A
   C. 22000 A
   D. 2640 A
   Answer: D. 22000 x pi x 0.306/8 = 2640 A; doubling ac doubles it. (Key point: Example)

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