D.C. MOTORS

D.C. motors have a place of pride as far as electrical drives are considered. The simplicity, and linearity of the control method makes them highly preferred machines in precision drives. In spite of the great advancements in a.c. drives these machines are still sought after by the industries. Apart from high precision application they are preferred in stand alone systems working on batteries and high speed drives on 

constant voltage mains. After the field is excited if we pass a current through the armature the rotor experiences a torque and starts rotating. The direction of the torque can be readily obtained from the law of interaction. These moving conductors cut the field and induce emf, usually called the 'back emf' according to Lenz's law and act as a sink of electrical power from the electrical source. This absorbed power appears as mechanical power. The converted mechanical power should overcome the frictional and iron losses before useful work could be done by the same. The connections to the supply of a d.c. shunt motor are given in Fig. 41.