DCMOTOR HIGH TORQUE STARTING ELECTRICAL|Online electrical engineering & Electrical Interview Questions

Thursday, August 15, 2013


Here is another electrical question from one of our followers.Why DC Motor has high torque?

All motors have two main parts which is the stator and rotor.The field windings constitute the stator and the armature windings constitute the rotor part.Usually the DC Series motor have low armature resistance.when the voltage is supplied there is high armature current which flows in.It works on the basic Ohm's law principle.
I= V/R.

Torque is directly proportional to the armature current.So the high current gives a high starting torque in the DC motor.When the rotor starts rotating, the back EMF is produced and it opposes the applied voltage.As the speed picks up the back EMF also rises and hence the resultant EMF is reduced.As the resultant EMF reduces, the armature current reduces and in turn reduces the torque.

The torque reaches the steady state when the armature current reduces.Usually the DC motor uses the external resistance to reduce the armature current.Till late 1980s DC motor was used for electric traction and after the advancement in power electronics, AC Induction motors have replaced the DC motor in traction.

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