Three-Phase Synchronous Machines

Syllabus of Three-Phase Synchronous Generator
Synchronous generator construction.
Construction details of a field and armature:
1.Rotating-Armature type:
2.Rotating-field type
Advantages of rotating field and stationary armature system

1.Ease of construction for large three-phase SYG. Since the armature winding is more complex than the field winding.
2.Number of slip-rings required only two slip-rings.
3.It is easier to insulate the armature coils from the core if the windings are placed on the stator instead of on the rotor.
4.The weight of the field system placed on the rotor is comparatively much lower than the armature windings placed on stator.
5.Improved ventilation arrangement air-cooling or/and hydrogen cooling for large gen. can easily be made on a stationary armature

Cylindrical and salient-pole rotor construction.
Equivalent circuit of a synchronous generator.
The phasor diagram of a synchronous generator with different load.
Power-flow diagram of a synchronous generator.
The effect of load change on a synchronous generator operating alone.
The condition required for paralleling.
Operation and share of generators in parallel with large power system.
Three lamp method
*If all the lamps glow together and become dark together then the phase sequence of the incoming alternator is the same as that of the bus-bar.
*If the lamps brighten in succession, then the systems have the opposite phase sequence, and one of the sequences must be reversed
Synchroscope:
A synchroscope is an instrument that indicates by means of a revolving pointer the phase difference and frequency difference between the voltages of the incoming alternator and the bus-bars
Summary:
When a generator is operating by itself supplying the system loads (alone):
1.The real and reactive power supplied by the generator will be the amount demanded by the attached load.
2.The governor set points of the generator will control the operating frequency of the power system.
3.The field current set points control the terminal voltage of the power system.
When a generator is operating in parallel with an infinite bus-bar:
1.The frequency and terminal voltage of the generator are controlled by the system to which it is connected.
2.The governor set points of the generator control the real power supplied by the generator to system.
3.The field current in the generator controls the reactive power supplied by the generator to the system.