Correct Answer : Option (A) :   DC motors

Explanation : The Ward Leonard system was implemented and used to control the speed of DC shunt electric motors. Previously, it was quite convenient to obtain a variety of speeds and reversing for industrial applications. The system consisted of any prime mover, including an AC motor driving a DC shunt generator. The armature of the DC generator was directly connected to the shunt motor's armature to be controlled. The DC motor had its magnetic field continuously excited while that of the DC generator, the magnetic field could be controlled in intensity and direction. As the prime mover rotated, the field of the DC generator was adjusted as required, hence its armature current-controlled, this current would be adjusted in magnitude and direction, and this, being fed to the armature of the DC motor, would create a driving torque as it reacted with the continuously applied motor field.