Armature Winding

In this  winding the working  emf is induced by the working  flux.

The current  which is  dependent on the load  called current.  The windings  that handles only exciting current  is called  field winding. Current in fields  windings is  always DC. It is also  known  as fields current  of magnetizing current. It  produces only a working  magnetic  flux. It is independent to load. Armature winding  carries only  load current.

Before  discussing the  methods  of speed  control  of DC  motor  it is important to know about  the classification of DC  motor. According to  excitation of the  filed self excited DC motor further  divided  into three types Dc series motor  shunt  motor and DC compound  motor.

                                                              Figure  DC Motor Separately excited(b)  Shunt (c) Series (d) Compound

The commonly used DC  motors  are shown  in  separately excited  motor the  field and armature voltage  can be controlled independent of each other. In  a shunt  motor field and armature are connected common  source. In case of  a series  motor fields current is  some as armature current and  therefore  fields flux  is a functions  of armature current. In  a compound motor  the mmf  of the  series  fields is  a functions  of armature current  and is in the  same direction as  mmf  of the shunt  fields.

For  separately excited and  shunt motors it is equal to  the resistance of armature  windings  and for series  and compound motors it is the sum of armature and fields  winding resistances.