By definition, it is an electromechanical machine which converts electrical energy into mechanical energy.
By principle, when a current carrying conductor is placed in magnetic field, it experiences a force (Flemings Left hand rule)
• The direct current (dc) machine can be used as a motor or as a generator.
• DC Machine is most often used for a motor.
• The major advantages of dc machines are the easy speed and torque regulation.
• However, their application is limited to mills, mines and trains. As examples, trolleys and underground subway cars may use dc motors.
• In the past, automobiles were equipped with dc dynamos to charge their batteries.
• The electronically controlled ac drives are gradually replacing the dc motor drives in factories.