Which of the following statements does NOT come under the advantages of stationary armature in an alternator?

The correct answer is option 2.

Construction of alternator

The alternator consists of a stator and a rotor. 

The 3ϕ AC supply is given on the stator while a DC supply is provided on the rotor. Hence, it is a doubly exciting machine.

In an alternator, the armature windings are placed on the stator while the field winding is placed on the rotor. This is done due to the following advantages:

1. When a stationary armature is used in the alternator, the output current can be taken directly from the fixed terminals on the stationary armature without using slip rings, brushes, etc. Hence, sparking at brushes is completely avoided.
2. The armature windings of the rotating field alternator, being stationary, are not subjected to vibration and centrifugal forces.
3. When the stationary armature is used, the armature windings can be braced better mechanically against the high electromagnetic forces due to large short circuit currents.
4. A stationary armature can be easily insulated for the high voltage for which the alternator is designed. This generated voltage may be as high as 33 kV.
5. The rotating field is supplied with the direct current. Thus, only two slip rings are required to provide direct current for the rotating field. 
6. A stationary armature may be cooled easily because the size of the armature can be increased to provide more cooling ducts.