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 3Ø armature winding is placed in the stator. This have following advantages:
1.
1. 
will increase.
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
=9056 A
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.
