dc machines

Electrical Machines

Electrical
Machine
Stationary
Transformer

Rotating
DC

AC
Motor

Induction

Generator

Motor
Generator
Synchronous
Motor
Generator

Electrical Generator / Motors
 An electric generator converts mechanical energy into electrical energy.
 An electric motor converts electrical energy into mechanical energy. Mechanical Input

Electrical input

ELECTRICAL
MACHINES
Generator

ELECTRICAL
MACHINES
Motor

Electrical Output

Mechanical output

 If current caring conductor is placed in magnetic field then a force is generated on current caring conductor.

F = BIL. Sinθ
If all three B and L are Perpendicular to each other, then
F = BIL
 If a conductor is moving in magnetic field then an EMF is generated in a conductor .
E = BVL. Sinθ
E = BVL

If B is Perpendicular to V

Basic Principles
 For magnetic field density (B):
1. Magnetic Fields:
 Direction of Field: North  South

2. Electro Magnetic Fields:

- Current caring conductor produces magnetic field around conductor.

Electromagnetism

Conductor

I
B, H

F

N

F = BIL

S

Construction of DC Machine
 Stator:
- Yoke (or Frame)
- Poles & Pole shoe
- Field windings
- Brushes
- End covers
 Rotor (Armature)
- Armature core
- Armature winding
- Commutator
- Shaft

General arrangement of a dc machine
(Cross- section of typical d.c. machine)

Diagram of a Simple DC Machine

Two Pole DC Machine

Four pole DC Machine

Yoke
Position :
 Outermost cover of the d.c. machine
Functions:
 It provides mechanical supports to the poles
 It provides protection from harmful atmospheric elements like moisture, dust & various gas like SO2,acidic fumes etc. to d.c. machine  It provides low reluctance path to magnetic flux
Material:
 It is prepared by using cast iron because it is cheapest.
 For large machines cast steel, silicon steel is used which provides high permeability.