268 



ELECTRICAL MACHINERY 



read to any extent. Hence this current indicated by A 

 must be a reactive current, 90 out of phase with the ter- 



minal voltage of the genera- 

 tor. The reactive current cir- 

 culates between the various 

 armatures and does not ga 

 into the load circuit at all; 

 it is therefore called a circu- 

 lating current. 



The reason for this circu- 

 lating current may be seen 

 by reference to Figs. 164 and 

 165. Let us suppose only 

 two alternators in parallel 

 supplying some power to a 



load drCuit ' als that No ' 



load. 



Ammeter 

 Wattmeter 



D.C. 



I I 



ovwww 



FIG. 163.-Connection of Alter- 

 nator to Bus-bars, through 2 nas J ust ^ een synchronized 

 Proper Meters. and so is furnishing practi- 



cally none of the power to the 

 Consider the local circuit made up of the two 



armatures and bus bars, all in series with each other. If 

 the voltage of No. 2 is just the same as that of the bus bars 

 (this condition is obtained before synchronizing), there is 



til I y 



No. 2 No. 2 



FIG. 164. Parallel Connection of Alternators. 



no resultant voltage in the local circuit and no current 

 flows around this circuit. The vector diagram for this 

 condition is shown in Fig. 165, where OE\ gives the voltage 

 of machine No. 1 and OE2 gives that of machine No. 2. 

 Evidently the resultant of these two e.m.fs. is zero. 



