A 240V dc shunt motor has armature and field resistances 0.2 W and 320 W respectively.  The motor drives a load at a speed of 950 rev min-1 and the armature current is 50A.  Assuming that the flux is directly proportional to the field current, calculate the additional resistance necessary in the field circuit to increase the speed to 1100 rev min-1 while maintaining the armature current constant. Calculate the speed of the machine with the original field current and an armature current of 90A

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Speed control of motor

Speed control by DC motor-speed controller is required to realize variable speed drive. Whenever a motor drives a particular load, it is called drive, and variable speed drive refers to a load requiring variable speed. All this is obtained by a DC motor speed controller.