324 ELEMENTS OF ELECTRICAL ENGINEERING. 



Other generators being in operation and connected to the main 

 buses, the generator which belongs to the panel shown in Fig. 

 275 is started as follows: The "starting plug" is inserted into 

 the synchronizing receptacle ("running plugs" being in the 

 synchronizing receptacles of all the machines which are already 

 in operation), and the exciter is started and brought up to full 

 speed. The new generator is then started and brought up to 

 approximately full speed, its field rheostat is adjusted until the 

 voltmeter shows that its voltage is approximately the same as 

 the voltage across the main bus-bars, then the speed of the driv- 

 ing engine is carefully adjusted until the synchronizing device 

 (either synchronizing lamps or a dial synchronizer) shows that 

 the two necessary conditions which are explained on page 155 

 are satisfied, and then the three-phase single-throw oil switch is 

 closed so as to connect the alternating-current generator to the 

 bus-bars. The generator is then in full operation and the " run- 

 ning plug" is put in place of the "starting plug" in the synchro- 

 nizing receptacle. 



In the case of direct-current generators operating in parallel, 

 the ammeters indicate the relative loads on the two machines. 

 In the case of alternating-current generators operating in parallel, 

 however, the ammeters on two machines may give the same indi- 

 cation and still the power output of one machine may be much 

 greater than that of the other. It is desirable, therefore, to install 

 a wattmeter on each generator panel so that the approximate * 

 power output of each generator may be indicated, and the field 

 rheostats of the generators adjusted to make them share the 

 station load equally. 



In many cases the ammeters for indicating the alternating-cur- 

 rent delivered by each phase of an alternating-current generator 

 are connected through current transformers. In Fig. 275, however, 

 the ammeters are shown inserted directly in the generator leads. 



* A single wattmeter indicates the approximate value of the power delivered by a 

 polyphase generator when the system is approximately balanced, as explained on 

 page 112. 



