The series field winding has low resistance while the stunt field winding has high resistance. Why?

  • The series filed winding is always connected in series with the armature and thus has to carry the armature current which directly gets decided by the load.
  • Thus the current passing through series field winding is of high level.
  • The voltage drop across series field winding gets added to the voltage drop across armature winding while deciding the back emf. This voltage drop must be very small.
  • Hence as the current through series field winding is high, in order to keep voltage drop across it to a small value, its resistance is very low.
  • On the other hand, the shunt field winding is directly connected across the rated supply voltage hence to limit current through it, resistance is very high.