THEOKY OF SYNCHRONOUS MOTOR. 



129 



whence 



e = 



= li 

 _IE 

 = 2r 



Thus at maximum output we have- 



(5) 



W = -r- 



4-r 



. E 

 t = 2r 



IE 



(6) 



It follows that e is greater than, equal to, or less than E, accord- 

 ing as / is greater than, equal 

 to, or less than 2r; that is, 

 the P.D. impressed between 

 the motor terminals need 

 not necessarily be greater 



than the counter E.M.F. 



, , 



developed by the motor. 



A graphic representation of the general phase relationships is 

 given in Fig. 42. In the case of maximum output ^ is zero. 



FIG. 42. 



LIGHT LOAD. 



84. In the case of the motor running on light load, we may, 

 if we neglect the friction of the bearings, etc , put w = 0, so that 



by (l)- 



i 2 r iE cos ^/ 

 and 



ie cos (j> = 



This shows that 



Also the maximum current at light load is (putting ^ = 0) given 

 by- 



(7) 



K 



