THE INDUCTION MOTOR. 



50. For equal air-gaps we have 



o.n 

 (TI = 0.0224 f- = 0.0396 



a\i = 0.0664 

 Hence, 



on 0.0664 



<TI 0.0396 

 or, in other words, 



= 1.68, 



_ _ 

 ffi ' " in' 



51. The leakage factor is inversely proportional to the pole-pitch, or 

 directly proportional to the number of poles. 



52. By the above experiments it has been demonstrated that the leak- 

 age factor is directly proportional to the air-gap, and inversely pro- 

 portional to the pole-pitch. We may, therefore, write the formula 

 for the leakage factor, 



in which equation c is a factor dependent upon the shape and size of 

 the slots, and upon a great many other conditions of which we are 

 still profoundly ignorant. For practical purposes, however, c can be 

 determined with satisfactory accuracy, though it will still be left to 

 the designer to estimate the value of c between certain limits. For 

 slots, as shown in Fig. 19, c varies between 10 and 15. 



WINDING THE SAME MOTOR FOR DIFFERENT SPEEDS. 



53. Formula (12) permits us to determine the change in the output, 

 power factor, and so forth, of a motor wound for a different number 

 of poles, for instance, for eight, four, or two poles. If the field has 48 

 or 72 slots, it can easily be wound so as to satisfy this demand. We 

 will assume the induction in the air-gap, or, which is the same, in the 

 teeth, to remain constant for all three cases. We will further assume 

 that the motors are to be wound for the same voltage. Then it is 

 clear, according to equation (5), that the total number of active con- 



36 



