288 



ELECTRICAL ENGINEERING 



a voltage proportional to the reactance drop in the line. This 

 voltage is transferred to the compensator circuit by the transformer 

 TI which also forms the reactance. Thus there are in the com- 

 pensator circuit three voltages proportional respectively to the 

 generator voltage and the resistance and reactance drops. If the 

 same proportions are maintained in each case, the voltage between 

 the terminals A B will be proportional to the voltage at the end of 

 the line, and, therefore, if the potential coil of the regulator is 

 connected across AB it will maintain a constant voltage at the 

 receiver end of the line. In the case of transmission lines of very 

 high voltage a correction must be made for the capacity of the 

 lines. The compensator shown is arranged for a single-phase cir- 

 cuit. With a three-phase alternator, as in Fig. 262, two current 

 transformers must be used connected as shown in Fig. 263(6). 



Threc-phaie Generator 



.S.inglc-phase 



(6) Three-phase 



FIG. 263. Line compensator. 



One automatic voltage regulator can be applied to control the 

 voltage of a system operating two or more alternators in parallel. 



The regulator may also be applied to the exciter of a synchro- 

 nous compensator to maintain a constant power factor at the 

 receiver end of the line. 



176. Synchroscope. A synchroscope is an instrument which 

 indicates, (1) whether the incoming machine is running too fast 

 or too slow and (2) the exact instant when synchronism is reached. 



One form of synchroscope is shown in Fig. 264. It has a lami- 

 nated bipolar magnetic circuit M excited by field coils FF, which 

 are connected across the alternating-current bus bars at (1) and 

 (2) and produce an alternating field. The core C is also lami- 

 nated and carries two windings A and B at right angles to one 

 another. Their common terminal is connected to one side of 

 the incoming machine at (4). The other terminals of A and B 

 are connected through a resistance r and a reactance x respectively 

 to the other side of the machine at (3). 



