Working Principle of DC Motor


Principle of D.C. Motor :


     Basically, the constructional of a d.c. generator and a d.c. motor are same. In fact we can use a same d.c. machine as a generator or as a motor. d.c. motors are also classified in the same fashion as d.c. generators according to the field winding connections like shunt, series and compound motors. 

Working Principle of DC Motor

     Consider a current carrying conductor placed in a magnetic field. Assuming the current flowing in the conductor is away from the observer shown by a cross, establishes the magnetic flux around the conductor rotating in clock wise direction. This flux weaken the main flux on left side and strengthens on right side of the conductor. The flux concentrated on right side of the conductor pushes the conductor towards the left with a force, F = BIL newton because, the magnetic lines of force move always in straight lines.

Working Principle of DC Motor

     The working principle of a d.c.motor also can be understood by considering a part of a multi-polar d.c. motor. When the terminals of a d.c. motor are connected to the d.c. supply source :

(i) The supply is given to the field magnets, which in turn develops magnetic poles. 

(ii) The emf is induced in the armature conductors.

Working Principle of DC Motor

     Armature conductors under N-poles are assumed to carry current away from the observer shown by crosses and those under S-poles to carry current towards the observer shown by dots. Applying Fleming's left hand rule, the direction of the force on each conductor can be found and is shown by small arrows on each conductor. It will be seen that each conductor experiences a force F which tends to rotate the armature in anti-clock wise direction. These forces on a armature will result in producing a driving torque which tends the armature to rotate.



Principle of Action of D.C. Motor :     


     The operation of a d.c. motor is based on the principle that when a conductor carrying current is placed in a magnetic field, the conductor experiences a torque or force on it. The direction of this force is given from fleming's left hand rule and magnitude is given by :

F  =  B I L newton

where

       F = force in newton

       B = flux density in Tesla

       I  = current in ampere

       L = conductor length in metre.



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