Question

In an alternator, field is placed on the rotor because of:
1. large current in the stator
2. large power in the stator
3. insulation of voltage which is made easy on stator than on rotor
4. small power in field circuit

Answer 1

Correct Answer - Option 3 : insulation of voltage which is made easy on stator than on rotor

Advantages of the stationary armature and rotating field:

The field winding of an alternator is placed on the rotor and is connected to the DC supply through two slip rings. There are various advantages of the stationary armature and rotating field system.

• It is easier to insulate stationary winding for high voltages for which the alternators are usually designed.
• The stationary 3-phase armature can be directly connected to load without going through large, unreliable slip rings and brushes.
• Only two slip rings are required for DC supply to the field winding on the rotor. Since the exciting current is small, the slip rings and brush gear required are of light construction.
• Due to the simple and robust construction of the rotor, a higher speed of rotating DC field is possible. This increases the output obtainable for a machine of a given size.
• For large rating alternators, the construction of armature on the rotor becomes more complex.