THE ALTERNATING CURRENT GENERATOR 267 



is put on and the voltage is adjusted to approximately equal 

 that of the line; the synchronizing device is then put in 

 the circuit and the speed is again adjusted until the differ- 

 ence in frequency is very small, say, ten alternations per 

 minute (this figure will vary with different operators and 

 different machines). A final adjustment of the voltage 

 is now made to make it within one or two per cent of that 

 of the line and, when the synchronizing device indicates 

 the proper phase relation, the synchronizing switch is 

 quickly closed. If the operator makes a bad " shot," i.e., 

 closes the switch either too soon or too late, an. excessive 

 current will result in the armature and the protective 

 devices will open and then another attempt must be made. 



This discussion of synchronizing holds good for any 

 synchronous machine; either alternator, synchronous motor 

 or synchronous converter. 



66. Circulating Current. Immediately after the alter- 

 nator has been synchronized, it takes no load at all; in this 

 respect it is similar to a c-c. machine which has just been 

 paralleled with the station bus bars. When c-c. machines 

 are operating in parallel and it is desired to have one of 

 the machines take more load, the voltage of this generator 

 is raised and it will increase its load in proportion to the 

 increase in its generated voltage. 



Effect of Varying the Excitation of the Alternator. If it 

 is desired to make the incoming alternator take load the 

 natural thing to do is to increase its generated voltage 

 by cutting out some of the field rheostat the same as is 

 done with a c-c. generator. But such a procedure does not 

 make the alternator take load at all; the generator ammeter 

 indicates a current almost proportional to the increase in 

 excitation, but the generator output wattmeter gives 

 scarcely any reading. 



Fig. 163 shows the alternator connected to the bus bars 

 through its ammeter and wattmeter. Increasing the 

 excitation increases the reading of A but does not make W 



