36 CONSTANT-VOLTAGE TRANSMISSION 



generator end and steady voltage at the receiver end. 

 By installing a small number of synchronous motors 

 at the receiver, and continually adjusting them to give 

 as constant voltage as possible, the generators may be 

 operated with only 10 per cent voltage variation. The 

 line is thus midway between a varying-voltage line and 

 a constant-voltage line, since twice the number of syn- 

 chronous motors would hold the voltage steady at both 

 ends of the line. Thus, without making any changes in 

 the construction of the line itself, it is possible to install 

 a single small synchronous phase modifier and obtain a 

 proportionate improvement in closer regulation or in 

 increased carrying capacity. The operation of this first 

 unit can be observed and its value and reliability thor- 

 oughly tested before investing the capital needed to 

 change over completely to constant-voltage operation. 

 On this account, then, the constant-voltage method 

 should commend itself to any power system which is 

 already built and whose load is large or is growing, 

 since the adoption of the new method does not necessi- 

 tate any interruption to service, nor any considerable 

 risk as to investment of capital or reliability of the 

 service. 



In order to make the description of the constant- 

 voltage system complete, its disadvantages should be 

 described. First, as to reliability of operation, it is well 

 known that large synchronous motors are not always 

 ' considered to be reliable in connection with transmission 

 lines, owing to the danger of their dropping out of step. 

 This might produce large accidental variations in volt- 

 age, since the voltage of the transmission line is depen- 

 dent on the synchronous machines. However, modern 



