---
title: "DC machine and its construction parts"
subject: "Basic Electrical and Electronics Engineering"
chapter: 2
key: "semester_1/basic_electrical_and_electronics_engineering:dc-machine-construction"
source: https://www.bctengineer.com/q/semester_1/basic_electrical_and_electronics_engineering/dc-machine-construction
site: BCT Engineering
---

# DC machine and its construction parts

Basic Electrical and Electronics Engineering · Chapter 2: Electrical Machines

- Asked in: 2081 Chaitra (new course), 6 marks
- Video: [DC Machine: Construction And Working Principle (DC Motor & DC Generator)](https://www.youtube.com/watch?v=oI-O9FCDqmg) — Electrical4U
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/basic_electrical_and_electronics_engineering/dc-machine-construction
- Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_and_electronics_engineering/chapter-2

## Question

Define DC machine and describe the different parts related to construction of DC Machine.

## Short answer

Main parts include yoke, field poles with field winding, laminated armature core with winding, commutator with brushes, and shaft. The commutator rectifies AC to DC in a generator or reverses current in a motor.

## Answer

A **DC machine** is an electromechanical energy converter. As a generator it converts mechanical energy into DC electrical energy; as a motor it converts DC electrical energy into mechanical energy. Construction is the same for both.

```text
   Yoke
  +------------------------------+
  |  Pole core + pole shoe  (N)  |
  |   field winding              |
  |      +---------------+       |
  |      | Armature core |<-shaft|
  |      | + winding     |       |
  |      | Commutator    |-brush |
  |      +---------------+       |
  |  Pole core + pole shoe  (S)  |
  +------------------------------+
```

**Main parts:**
1. **Yoke (frame):** the outer cast-iron or cast-steel ring. It supports the poles, carries the return flux and protects the machine.
2. **Poles and pole shoes:** laminated steel poles bolted to the yoke carry the field winding. The shoe spreads the flux evenly over the air gap and supports the coils.
3. **Field winding:** coils of insulated copper on the poles; excited with DC to produce the main flux.
4. **Armature core:** a cylinder of laminated silicon steel with slots, mounted on the shaft. Lamination reduces eddy-current loss.
5. **Armature winding:** copper conductors in the slots, connected as lap or wave winding, where the emf is induced.
6. **Commutator:** copper segments insulated by mica, joined to the armature coils. It converts the alternating emf in the armature to unidirectional output (generator) or reverses the current for continuous torque (motor).
7. **Brushes and brush gear:** carbon or graphite blocks held by springs against the commutator, to collect or supply current.
8. **Shaft, bearings and end covers:** carry the rotating parts and keep the air gap uniform.
9. **Interpoles** (optional) improve commutation, and a **fan** cools the machine.

## Check yourself

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

1. What is the role of the yoke?
   A. Collects current from the commutator
   B. Supports the poles, carries return flux and protects the machine
   C. Carries the armature winding
   D. Reverses the current
   Answer: B. The cast-iron or steel yoke is the frame and a path for return flux. (Key point: Yoke)

2. What does the pole shoe do?
   A. Cools the machine
   B. Reverses the field
   C. Spreads flux evenly over the air gap and supports the field coils
   D. Connects to brushes
   Answer: C. The enlarged pole tip distributes flux and holds the coils. (Key point: Pole shoe)

3. What does the commutator do?
   A. Converts armature AC emf to unidirectional output (generator) or reverses current for continuous torque (motor)
   B. Produces the main flux
   C. Keeps the air gap uniform
   D. Cools the winding
   Answer: A. Copper segments, insulated by mica, rectify or switch the armature current. (Key point: Commutator)

4. Why is the armature core made of laminated silicon steel?
   A. To increase hysteresis
   B. To reduce copper loss
   C. To increase weight
   D. To reduce eddy-current loss
   Answer: D. Thin insulated sheets limit eddy currents induced in the rotating core. (Key point: Armature core lamination)

## Related in other subjects

- [DC generator construction, working, emf](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machine%3Adc-generator-construction-emf) — Electrical Machine, chapter 3
- [Choice of number of poles in DC machine](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adc-number-of-poles) — Electric Machine Design, chapter 5, asked 8×
- [Choice of ampere conductors per meter in DC machine](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adc-ampere-conductors-selection) — Electric Machine Design, chapter 5, asked 4×
- [Output equation of DC machine](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adc-output-equation) — Electric Machine Design, chapter 5, asked 3×