CHAPTER IV 



POWER-FACTOR CONTROL OF LINE VOLTAGE 



THE most common means at present for making 

 adjustments in line voltage so as to deliver steady volt- 

 age to customers consists in using a potential regulator. 

 This consists generally of a low-voltage transformer in 

 series with the line, so that it adds a certain amount of 

 voltage directly to the line voltage. An electric relay 

 operates a mechanical device which changes this incre- 

 ment of voltage in accordance with changes in the load 

 and potential, in such a manner that a, constant voltage 

 is kept at the centre of load of the line. Potential regu- 

 lators are exceedingly useful and reliable pieces of ap- 

 paratus, and they are extensively used on the feeders of 

 distribution systems. It is the purpose of this book, 

 however, to discuss the fact that synchronous motors 

 can also be used as potential regulators. They are not 

 in very direct competition with the above-described 

 transformer type of potential regulator, since the field of 

 application of synchronous motors is with large blocks 

 of power, and especially with transmission lines. 



It is a very firmly entrenched idea, but correct only 

 for certain applications, that synchronous motors should 

 be used in alternating-current systems only in order to 

 raise the power-factor of the load on the generators from 

 a low to a high value, and that 100 per cent power-factor 

 at all times is the ideal condition. Synchronous motors, 

 when employed for this purpose, may be said to be used 



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