VOLTAGE REGULATION 



371 



obtainable across the main generator fields will be from 200 (the 

 difference between 250 and 50) to 300 volts (the sum of 250 and 50 

 volts). 



High-voltage, High-current Relays. A cut-out relay has been 

 devised to be used in connection with T.A. regulators for guarding 

 against short circuits and voltage rises in transmission systems. If 

 a voltage regulator is used and a short circuit should occur some- 

 where on the system, for example, in the transmission lines, the 

 action of the regulator would naturally be to deliver the maximum 

 excitation to the fields of the exciters and generators, so as to keep 

 up the voltage of the system. This, in turn, necessitates that the 



FIG. 223. Connections of High-voltage, High-current Cut-out Relay with 

 Type T.A. Voltage Regulator and Two Exciters in Parallel. 



governors of the prime movers be wide open, and if the short cir- 

 cuit should be suddenly relieved, the voltage often rises to very 

 high values, owing to the time element involved in closing the 

 governors and in demagnetizing the fields. The connections for a 

 high-voltage, high-current relay operating in connection with two 

 exciters and one T.A. regulator are shown in Fig. 223. The relay 

 is provided with a current coil and a potential coil, and will 

 automatically insert resistance in the exciter field and thus reduce 

 the exciter voltage in case of excessive loads or voltages on the 

 main system. 



Synchronous Condenser Regulation. The question of regula- 

 tion of large high-voltage systems involves a number of difficul- 



