SYNCHRONOUS MOTORS. 291 



generator is seen to be far higher than in the case of 

 equal excitation of the machines, but the product of OE. Z , 

 and OCft is the same as in Fig. 136. 



It is to be noted that the angle of lag of the current 

 in the circuit joining the machines is C O E r in each case, 

 and the cosine of this angle would be the power-factor of 

 the circuit. The power transmitted from one machine to 

 the other would be measured by a wattmeter with its 

 current coil inserted in this circuit and its volt coil con- 

 nected to the terminals of either machine. The angle 

 of phase difference between the armature back voltage of 

 either machine and the circulating current would be E l C 

 and E 2 C respectively, but this could not be obtained by 

 any method of direct measurement. 



The voltages measured at the terminals of the generator 

 and motor will be equal, except for the small loss in the 

 line, which may be neglected for the present. This does 

 not, however, mean that the electromotive force generated 

 in the armature of the alternator is equal to the back electro- 

 motive force generated in the motor armature. As in the 

 case of corresponding direct-current machines the voltage 

 at the generator terminals = total voltage generated - 

 volts lost in armature ; while in the case of the motor the 

 terminal voltage = back electromotive force + volts lost in 

 the armature. 



It must be borne in mind that the various voltages are 

 not in phase with each other, and the negative or positive 

 sign must be taken to apply to vector summation and not 

 algebraic summation. 



Case 3. Two Alternators in Parallel Supplying Current to an 

 Outside Circuit. This condition is similar to that considered 

 in Case 1, with the addition of an added current flow- 

 ing through the armatures of the machines to the 

 external circuit. This current does not affect the inter- 

 action of the two machines in any material way so long 

 as the output of both remains equal. It will reduce the 

 external voltage of the machines slightly, and this will 

 produce a small modification in the voltage diagram 

 already given. Even when the machinese are not 

 quite equally excited, or when one tends to fall 

 behind the other in step, the diagrams already given 

 apply. The diagrams should in each case represent the 



