Q:- when a AC supply is given to a DC motor, it does not rotate & What is the reason.....? ( sai saikumar jn )

   Q:-  When a A.C supply is given to a D.C motor , it does not rotate.
Q. What is the reason?


 Ans:- At first think how a D.C. motor works. When the coil inside the magnetic field rotates you get the mechanical energy from electric energy. In the case of DC motor the rotation in one direction is kept continuous by slip ring and brush so that we get mechanical energy continuously. But if you pass ac current through the DC motor, as a result of changing direction of current the rotation of the coil will change with respect to time. So the coil will not rotate totally rather it will vibrate.

 Frequency of the vibration will be equal to the frequency of the AC current. So the motor will not run in the way it generally runs.

Shunt wound DC motors are not suitable for AC operation because the difference in inductance between the armature and the field causes a relative phase shift between the armature current and the field current. For a DC motor to operate with AC current, the armature and field currents must reverse at exactly the same time, as they do when the windings are connected in series.

 For reasonably good performance, the cores need to be laminated and the brush position needs to be set to 90°.

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