146 



ELEMENTS OF ELECTRICAL ENGINEERING. 

 AB A 2 



P' = 



cos0 (16) 



These equations, (15) and (16), are the fundamental equations 

 of the synchronous motor. Of course the algebraic sum of P' 

 and P" is equal to RP. 



A very clear idea of the variations of P" with < is given by 

 the variation of OQ, Fig. 125, and a clear idea of the variation 

 of P' with < is given by the variation of O f Q 1 , Fig. 126. 

 This variation of P f and and P" with <f> is extremely important 

 in the following physical discussion, and a clearer insight into this 

 variation may be obtained with the help of Figs. 127 and 128, 



Difference fi 



A = l, 100 volts. R = i.oo ohm. 



B = 1,000 volts. uL = 0.58 ohm. 



Fig. 127. 



in which the values of </> are represented as abscissas, and the 

 values of P> ', P", and RP(= P 1 + />") as ordinates. Figure 

 128 is an enlargement of the middle portion of Fig. 127, and the 

 ordinates of the curve 77 represent the values of the ratio P" / P 1 ', 

 disregarding sign. This ratio, when P" is an intake of power 

 by machine B (P" negative) and P' an output of power by 

 machine A (P 1 positive) is the efficiency, ignoring all losses 

 except the RI 2 loss in the circuit. 



