Advantages of Rotating field over Rotating armature

The various advantages of the rotating field can be stated as-

1. As everywhere ac is used, the generation level of ac voltage may be higher as 11 kV to 33 kV. This gets induced in the armature. For the stationary armature, large space can be provided to accommodate a large number of conductors and the insulation.
2. It is always better to protect high voltage winding from the centrifugal forces caused due to the rotation. So high voltage armature is generally kept stationary. The avoids the interaction of mechanical and electrical stresses.
3. It is easier to collect larger currents at very high voltages from a stationary member than from the slip ring and brush assembly. The voltage required to be supplied to the field is very low (110 V to 220 V) and hence can be easily supplied with the help of slip ring and brush assembly by keeping it rotating.
4. The problem of sparking at the slip rings can be avoided by keeping field rotating which is low voltage circuit and high voltage armature is stationary.
5. Due to the low voltage level on the field side, the insulation required is less and hence the field system has very low inertia. It is always better to rotate low inertia system than high inertia, as efforts required to rotate low inertia system are always less.
6. Rotating field makes the overall construction very simple. With simple, robust mechanical construction and low inertia of the rotor, It can be driven at high speeds. So greater output can be obtained from an alternator of a given size.
7. If the field is rotating, to excite it by an external dc supply two slip rings are enough. One each for positive and negative terminals. As against this, in the three-phase rotating armature, the minimum number of slip rings required is three and can not be easily insulated due to high voltage levels.
8. The ventilation arrangement for high voltage side can be improved it is kept stationary.

I hope that this article will be informative for you all.

Thanks and Regards

Er. Abhishek Srivastava