140 



ALTERNATING CURRENTS 



76. Paralleling or Synchronization of 

 Alternators 



Alternators are capable of being run in parallel like continuous- 

 current generators. In order to throw an additional alternator into 

 parallel with a number of others, it is necessary to adjust its 

 excitation, speed, and phase so that its e.m.f. is about equal to the 

 'bus bar p.d., is of the same frequency, and in phase opposition to the 

 p.d. This process of adjustment is known as paralleling or synchroniza- 

 tion, and the instrument or collection of apparatus by means of which 

 the proper phase relation is ascertained is termed a synchronizer. 



The arrangement of synchronizer connections suitable for a single- 

 phase machine is shown in Fig. 104. The synchronizer consists of 



INCOMINQ MACHINE 

 FIG. 104. Connections of Synchronizer. 



two small transformers and an incandescent lamp or voltmeter. The 

 primary PI of one transformer is across the 'bus bars, while that of 

 the other Pa is across the terminals of the incoming machine. The 

 secondaries Si and 83 are connected in series with each other and 

 with a lamp L (or voltmeter), the connections being so arranged that 

 when the e.m.f. of the incoming machine is in phase opposition to the 

 'bus bar p.d., the e.m.f.'s in the secondaries are added, and the lamp 

 L glows brightly.* The e.m.f. of the incoming machine is adjusted 

 to the desired value by means of the voltmeter V. When the machine 



* In some instances, the connections are arranged so that with phase opposition of 

 the 'bus bar p.d. and the machine e.m.f. the secondary e.m.f.'s oppose each other and 

 the lamp L is dark. Since, however, a brightly glowing lamp is far more sensitive to 

 small changes of voltage than a dark one, this arrangement is not to be recommended. 



