ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 25 
shape ; also the designer is more likely to perfect the design 
as regards shape, pitch and quality. 
The fixing of the magnet limbs on the wheel rim is a con- 
structional detail which must be carefully considered by 
the designer. Figs. 12 and 13 show two methods of fixing 
the magnet limbs on the wheel rim. 
On very large machines it is advisable to give the laminated 
magnet limbs the same rigidity and stability as that of the 
solid cast steel type. This can be attained by welding the 
———— 
Bb 
Fies. 12 AND 13.—METHODS OF FIXING POLE PIECES ON REVOLVING 
FIELD TyPE ALTERNATORS. 
surfaces which are not exposed to induction effects by any 
electrical method. 
50. Magnet Wheels.—For large generators with magnet 
wheels over four feet, the wheel should be cast in two or 
more parts, so as to avoid internal stress in the material. 
The different parts of the magnet wheel are connected to- 
gether by means of bolts and shrinking rings. 
For magnet wheels of about four feet, the splitting of the 
magnet wheel hub is sufficient to take up the internal stress, 
providing that the magnet rim is not too heavy, in order to 
obtain a flywheel effect in the generator. 
