THE ALTERNATING CURRENT GENERATOR 263 



The Wave Form Not Adjustable. The e.m.f. wave form 

 of an alternator is fixed by the design of the machine and 

 cannot be affected by the operator; however, practically 

 all modern machines give wave forms very nearly sinusoidal 

 so that the fourth condition is nearly always satisfied to a 

 degree sufficient for successful parallel running. 



Manipulation. The operation of manipulating the 

 incoming machine to bring about the first three conditions 

 and of closing the switch which connects it to the bus bars 

 is called synchronizing. It is evidently easy for the operator 

 to satisfy the first two requirements; the voltage of the 

 incoming machine may be varied by its field rheostat and 

 its frequency (depending directly upon the speed) may be 

 altered by changing the speed of its prime mover. To 

 satisfy the third condition a synchronizing device may be 

 used; either incandescent lamps, 

 properly connected between the machine 

 and bus bars, or a synchronoscope 

 (many times called a synchroscope) 

 may be used. 



The Synchronoscope. The syn- 

 chronoscope is an indicating instru- 

 ment having a dial over which a 

 finger rotates or oscillates. In the F IG< 153. Oscillating 

 better type (illustrated in Fig. 158) Synchronoscope. 



the finger merely oscillates back Weston Elec. Inst. Co. 

 and forth while the type shown in 



Fig. 159 has a circular dial and the finger rotates over the 

 complete circle. 



In either type there are two independent electrical 

 circuits, one of which is connected to the bus bars and 

 the other to the incoming machine. The magnetic fields 

 set up by these two circuits so react on one another .as to 

 make the needle either oscillate or rotate; a mark on the 

 dial shows the proper " synchronizing " position for the 

 needle and the synchronizing switch must not be closed 



