Dec 7, 2014

DC Motor Introduction, Principle and Working



DC motors are rarely utilized in normal applications as a result of all electrical supply firms furnish electrical energy but, for special applications like in steel mills, mines and electric traction, it's advantageous to convert AC into DC so as to use DC motors. The rationale is that speed/torque characteristics of DC motors are much more superior thereto of AC motors. Therefore, it's not stunning to notice that for industrial drives, DC motors are as common as 3-phase induction motors. Similar to DC generators, DC motors are also classified into 3 kinds; they are series-wound, shunt-wound and compound- wound. The employment of a specific motor depends upon the mechanical load it's to drive.

Principle of DC Motor

A machine which transforms the DC power into mechanical power is called as a DC motor. Its operation relies on the principle that once a current carrying conductor is placed in a very magnetic field, the conductor experiences a mechanical force. The direction of this force is given by Fleming’s left hand rule and magnitude is given by;

                                                               F=BIl newtons

Fundamentally, there's no constructional distinction between a DC motor and a DC generator. The same DC motor will be run as a generator or motor.

Working of DC Motor

Let’s think a part of a multipolar DC motor as shown in Fig. once the terminals of the motor are connected to an external DC supply. Then, 
The field magnets are excited developing alternate N and S poles;

The armature conductors carry currents. All conductors below N-pole carry currents in one direction whereas all the conductors below S-pole carry currents within the opposite direction.
Assume the conductors below N-pole carry currents into the plane of the paper and those below S-pole carry currents out of the plane of the paper which is shown in Fig. Since each armature conductor is carrying current and is placed within the magnetic field, mechanical force acts on that. Stating to the Fig and applying Fleming’s left hand rule, it's clear that force on every conductor is tending to rotate the armature in anticlockwise direction. All these forces add along to provide a driving torsion that sets the armature rotating. Once the conductor interchanges from one side of a brush to the opposite, the current in the conductor is reversed and at identical time it comes below the influence of next pole that is of reverse polarity. Accordingly, the direction of force on the conductor rests identical.


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