The field winding of an alternator is placed on the rotor and is connected to DC supply for producing the magnetic flux through slip rings/ brush-less excitation.
The 3 Ø armature winding is placed in the stator. This have following advantages:
Because in 210 MW unit the excitation current(2600 A) is very small the the alternator full load current(9050 A).
I = 210 x 10^6 / √3 x 15750 x .85
This much current will not possible to come out through slip ring/ brush
*2. More no of brush will required for 3Ø four wire STAR-CONNECTIONS.
3. The Output Voltage will reduced by the reduce of no of turns of conductor or Area.
4. Due to simple and robust construction of the rotor , Higher speed of rotating rotor is possible
5. The stationary 3-Phase armature can be directly connected to load without large unreliable slip ring and brushes.