SYNCHRONOUS GENERATORS 319 



can be considered to consist almost entirely of the reactance of the 

 circuit. The cross current will, therefore, have a magnetizing 

 effect on generator No. 1 and a demagnetizing effect on generator 

 No. 2, and consequently keep the voltages the same. The cross 

 current is wattless, consuming no power except that corresponding 

 to the PR loss in the circuit. It is thus evident from the above 

 that a change in the field excitation can h?.ve no effect on the load 

 of the machine. 



If the excitation of the two machines is the same, but the gov- 

 ernor adjustments differ, a cross current will also be produced as 

 shown in Fig. 187. OA represents the induced e.m.f. of generator 

 No. 1, leading 6 degrees in advance of the bus-bar voltage, while 

 OB represents the induced e.m.f. of generator No. 2, lagging 6 

 degrees behind the bus-bar voltage. The resultant OC will cause 



Gen. 



FIG. 187. 



a cross current to flow and as the resistance of the circuit is small 

 compared to the reactance, it will lag nearly 90 behind OC, and 

 practically be in phase with the e.m.f. of generator No. 1, and in 

 opposition to the e.m.f. of generator No. 2. It will thus consume 

 power of the leading machine No. 1, that is, retard it, and supply 

 power to the lagging machine No. 2, that is, accelerate it, and thus 

 pull the two machines together. It is evident from the diagram 

 that it is the reactive component ID of the cross current that pro- 

 duces the synchronizing power, and that the power component 

 OD has no effect in this respect. A certain amount of reactance is 

 therefore necessary for a satisfactory synchronous operation, and 

 the larger the reactance is, compared to the resistance, the larger 

 is the synchronizing component of the cross current. Increasing 

 the reactance would, therefore, increase the synchronizing force, 



