324 



ELECTKICAL MACHINERY 



will merely " float " on the line, with its field considerably 

 overexcited. In such case it is called a synchronous 

 condenser. 



Vector Diagram of the Circuit. Fig. 211 illustrates the 

 operation of such a scheme. The current /' lags behind 



I 



Synchronous 



Motor, taking!, 



leading current] 



Load of Induction 



Motors, taking 

 lagging current 



FiQ. 211. Connection of Synchronous Motor to Compensate for the 

 Lagging Current of an Induction Motor Load. 



B 



the line voltage and the current I" is ahead of the line 

 voltage. Evidently under proper conditions the line 

 current / may be in phase with the line voltage. 



The vector relations in such a case are shown in Fig. 

 212. The current supplied to the 

 induction motor is shown at 01', 

 having the active component OD 

 and the reactive component, OA. 

 The synchronous condenser cur- 

 rent is shown at 07", having an 

 active component OC, just suffi- 

 cient to supply its own losses. 

 The field has been overexcited to 

 such an extent that its leading 

 component OB is j ust equal to A . 

 Evidently the line current 01 will 

 be in phase with the line voltage 

 OE, hence the line power will 

 be unity and the line carrying 

 capacity as great as is possible. 



It is not generally attempted to bring the power factor 

 of the line up to unity; this scheme of using a synchronous 



FIG. 212. Vector Diagram 

 of Currents, Showing how 

 the Combined Load May 

 have a Power Factor of 

 Unity. 



