400 



Mr. W. Duddell 



[May i: 



two of the poles of the stationary part of the machine. In order to 

 reduce the air friction on this disc, which is run at the very high speed 

 of 2<>,000 r.p.ra.,the spaces between the teeth have brass phigs riveted 

 into them so as to render the surface of the disc perfectly smooth. 

 Fig. 2 shows the complete disc and its shaft, and Fig. 3 a portion of 

 the disc on a larger scale. 



The frame of the machine F, Fig. 4, contains two field coils A. 

 The magnetic lines of force pass through the frame through the part 

 B and the laminated polar projections E. According to whether 

 there is an iron spoke or the non-magnetic material between the polar 

 projection E, the magnetic flux will be maximum or minimum, and 

 will consequently go through a complete cycle of change as each iron 



600 S/d Wmd/ng 



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Flux used mOOOSIotWindiiiq MM tfft tttt tttt tftt tftt ttft tttt 



riux used in 400 Slot Windinq ffff ' tttt tttt 



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400 Slot Winding 



Fig. G. — Winding Diagram, Alexanderson's Alternator. 



spoke passes the pole tips ; the wires in which the current is induced 

 are w'ound zigzag fashion around the pole tips. With 300 teeth and a 

 speed of 20,000 r.p.m., a frequency of 100,000 is obtainable. A view 

 of the complete machine is shown in Fig. 5, the driving motor l)eing 

 on the right, the gearing in the centre and the high frequency alter- 

 nator on the left. An output of some 2 k.w. is obtainable. In order 

 to get still higher frequencies without rendering the spacing excessively 

 small so that there is no room for the wires between the polar ])ro- 

 jections on the stator, another form of winding has been adoi)ted in 

 which instead of using GOO polar projections on the stator only 400 

 are used. This winding is illustrated in Fig. 6. 



With this latter type of winding, using 800 polar projections, a 



