THE INDUCTION MOTOR 273 



The torque developed per phase 



CE . 



V X CE is the total power per phase delivered to the rotor. 



The total power delivered to the rotor by n phases, P 2 = n X 

 V x CA' watts, 



horsepower output 



X V _ 2wN z T ( . 



~"746~~ " 33,000 



where T is the total torque. 



But N 2 = N * E from (D 



Substituting in (III) 



n X DE X V = 2Tr(NXDE)T 

 746 : CEX 33,000 



T = 7.04 nX V N X ^ pound-feet. 



7C = 7.04 X n ' (II) 



As the phases n, the voltage 7', and the synchronous speed N 

 are usually fixed, the torque 



r = X'C# where #' = 7.04 " * T ' 



112. The Measurement of Slip. There are various methods 

 for measuring slip. The slip may he determined by measuring 

 th- rotor speed and suht ract inir this speed from that of the rotat- 

 ing field as determined from the frequency. As the slip is hut a 

 very small percentage of either the synchronous speed or the 

 rotOI speed and is the difference of two nearly equal quantities, 

 it i< not po><ihle to determine it accurately hy the measurement 



h of these quantitie- and so finding their differenre. 

 A simple method of m -lip i- -liown in l-'ig. 252. A 



01 disc is fastened to the end of the -halt or to the 

 pulley of the motor. This di-c ha- the same numher of hlack 

 and the same numher of white Beoton as the motor has poles. 

 Tin- dlM i- illuminated hy an arc lamp which is fed from the 

 18 



