A rotating shaft is required to have an overhang for the mounting of a generator for an AC-exciter, the shaft length being increased correspondingly. The overhang may become the cause of generating shaft vibrations. A turbogenerator has a rotor over which a field winding is disposed, a coupling co-cut from a rotor shaft, an AC exciter for supplying a DC current to the field winding through a rectifier, and a generator for the AC-exciter, the generator including a permanent magnet as a field generator and supplying a DC current to a field winding of the AC exciter through the rectifier. The AC exciter and the generator are disposed over the rotor shaft. The rotor is rotated through engagement between a turbine and the coupling. The generator for the AC-exciter is mounted in a position on the side nearer to the turbine than a stator of the turbogenerator.
1. A turbogenerator comprising:
a stator having an armature winding;
a rotor having a field winding;
a coupling monolithically formed with a shaft of said rotor;
a rotary rectifier;
an AC exciter for supplying a DC current to said field winding through said rotary rectifier; a rotor bearing arrangement disposed at both sides of said shaft; and
a sub-exciter having a permanent magnet as a field generator, supplying a DC current to a field winding of said AC exciter, being arranged between a rotor bearing and said coupling at one side of said shaft, a stator of said sub-exciter being split in the circumferential direction, and said AC exciter arranged at a side of said stator other than the same side as that of said sub-exciter,
wherein said stator, said rotor, said coupling, said rotary rectifier, said AC exciter, and said sub-exciter are arranged over said shaft of said rotor, and
a pedestal portion for mounting the sub-exciter to the shaft of the rotor, the shaft of the rotor, the coupling and the pedestal portion are monolithically formed of a unitary piece of material.
2. The turbogenerator according to claim 1 , wherein the stator of said sub-exciter has an inner diameter smaller than an outer diameter of said coupling.
3. A turbogenerator according to claim 1 ,
wherein the permanent magnet of said sub-exciter is disposed between a pole shoe and a rotating shaft of said rotor.
4. The turbogenerator according to claim 3 , wherein said pole shoe has portions extending longer than an axial length of said permanent magnet, bolt holes are formed in the extending portions of said pole shoe, and said pole shoe is fixed to the rotating shaft of said rotor by bolts fastened into said bolt holes.
5. The turbogenerator according to claim 3 , wherein a minimum gap between a stator of said generator for alternating-current excitation and said rotor is not smaller than 5 mm.
6. The turbogenerator according to claim 3 , wherein assuming that a minimum gap between a stator of said generator for alternating-current excitation and said rotor is Ga and a thickness of said permanent magnet is Gm, the relationship of 0.9<Gm/Ga is satisfied.
7. The turbogenerator according to claim 1 , wherein a portion of said rotor in which said permanent magnet of said sub-exciter is disposed has an outer diameter larger than an outer diameter of the other portion of said rotor.