THE INDUCTION MOTOR. 



fore, also very nearly the output, vary in proportion to the pole- 



pitch. According to the diagram we find the leakage factor for the 



g 

 two-pole motor equal to -> = 0.05 ; for the four-pole motor equal to 



O 



-Q- 

 oo 



= o.io; and for the eight-pole motor equal to - = 0.20. The 



power factor in each case can now be calculated with the help of for- 

 mula (3). This is done in the following table: 



54. The output is therefore proportional ,to the number of r. p. m. 



55. It may not be amiss here to remark that if the motor is ordinarily 

 wound for four poles, the induction in the iron above the slots may 

 for the same frame become too high in the two-pole motor, thus in- 

 creasing the magnetizing current, and, possibly, creating undue 

 heating. 



DRAWBACKS OF A HIGH FREQUENCY. 



56. If the circumferential speed of the armature is limited, and this 

 is generally the case, then the pole-pitch is also limited for a given 

 number of r. p. m. The air-gap cannot indefinitely be diminished, 

 hence a high frequency necessitates a large leakage factor according to 

 formula (12). We labor here under the same difficulties that we have 

 met with in the design of alternators for high frequencies. 5 It is 

 doubtless possible to build motors for frequencies between 60 and 

 100, but the higher the frequency the lower will be the power factor, 

 the larger will be the lagging currents. It has also to be borne in 

 mind that motors for high frequencies, if they are to be as good as 

 those for low frequencies, must be made not inconsiderably larger. 



"See the author's papers in the ELECTRICAL WORLD AND ENGINEER, Jan. so, 27 

 and Feb. 3, 1900. 



38 



