1 66 ELEMENTS OF ELECTRICAL ENGINEERING. 



is also in phase with / when B is adjusted to give minimum / with given P f (or 

 with given / >// ). This correspondence is by no means self-evident. 



80. Maximum intake of machine B ; A, B, X and R being given. P*f 

 has its maximum negative value when cos (0 0) = I, and equation ( 15 ) becomes 



&CQSO A& 



* max. 



Fig. 141. 

 Figure 141 shows the state of affairs when intake of B (=: OQ] is at its greatest. 



81. Greatest value of the electromotive force B for which machine B can 

 act as a motor; A t X and R being given. So long as 



AB 

 is greater than 



then P // can have negative values according to equation (15). Therefore the lim- 

 iting case is where 



AB B* 



cos 6 



VR* -i- x* VR* -f- x* 



or 



B A 

 c 



This limiting case is shown in Fig. 142. 



