Principle of Operation for DC motor

PRINCIPLE OF OPERATION

The basic principle is whenever a current carrying conductor is placed in a magnetic field the conductor experiences a force whose direction is given by fleming's left-hand rule.

If a current carrying conductors is placed between two magnetic poles as shown in fig 3.23, both the fields will be distorted flux (less flux)

From the fig 3.23 above the conductor the field is weakened and below the conductor the field is strengthened. Therefore the conductor move upwards. The force exerted upwards depends upon the intensity of the main field flux and the magnitude of the current.

The direction of the current through the conductor is reversed as shown in fig 3.24. Here, below the conductor field is less weakened and above the conductor the field is strengthened. Then the conductor tends to move downwards.

The magnitude of the force experienced by the conductor is

F = BI Ɩ

Where

B - magnetic field density in wb/m²

I - current in ampere

Ɩ - length of the conductor in meters

The direction of motion is given by fleming's left hand rule, which states that, if the left thumb, force finger and middle finger of the left hand are three mutually perpendicular directions and if the fore finger indicates the direction of the field, and the middle finger indicates the direction of current, then the thumb points the direct of motion of the conductor.

 In a dc motor, a strong electromagnetic field and a large no of conductors housed in an armature and carrying current, make the armature rotate.