ALTERN’ TING. GENERATO«xS AND SYNCHRONOUS MOTORS. 5 
9. Limit of Use.—'This type of machine has not been used to 
any great extent, on account of the electrical and magnetic 
“isadvantages, due to the high leakage coefficient of the 
magnet system. This loss, however, can be greatly de- 
creased in high speed generators by reducing the number 
of poles. Besides mechanical advantages, the inductor type 
alternator gives somewhat better efficiency than the other 
types and its application can be recommended for small 
- eutputs, high speeds and low frequencies. 
Pig. 3 gives the general arrangement of an inductor generator 
in cross section and side view. 
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Fie. 3.—Inpuctor TyrPpE ALTERNATOR. 
10. Revolving Field Alternator.—The revolving field type 
machine is characterized by having a stationary armature 
and a revolving magnet wheel, to which the poles are 
attached by means of strong bolts or similar attachments. 
Fig. 4 represents a revolving field type generator in cross 
section and side view; Fig. 4A shows a similar type of 
machine in perspective. This class of alternator is seldom 
built for smaller outputs than, say, 10 K. W., because, for 
smaller outputs this type presents mechanical and com- 
mercial difficulties in finding room for the field coils. 
2. Limit of Use.—The revolving field generator is especially 
suitable for heavy work and high voltages in connection 
with any kind of prime mover, but its real value will be 
