DC Motors

There are three types of DC motors. They are shunt motor, series motor and compound motor.  The difference between these categories lies on the way their field windings are excited. In a shunt motor, the field winding is connected in parallel with the armature. When power supply is on, a constant voltage develops across the field windings since they are connected in parallel with armature. As a result, field current also remains constant which is independent of the load current.  Shunt field winding comprises of a large number of turns of fine wire. A shunt motor normally operates at constant speed and is adaptable to large speed variations. The main drawbacks of a shunt motor are low starting torque and overload torque capability.  In a series motor, excitation is achieved from a winding which is connected in series with the armature that carries load current. Excellent starting and superior overload torque characteristics are the main advantages of a series motor. But a main cause of concern in series motor is its dangerously high speed at zero load conditions since speed controlling is difficult in this type of motor. In a compound motor, excitation results from combined action of both shunt field winding and series field winding.