72 CONSTANT-VOLTAGE TRANSMISSION 



the advantages of a more constant generator voltage. 

 This is best shown by the attached example, where the 

 saving in power, allowing fully for the losses in the syn- 

 chronous phase modifiers, produces a large net saving 

 for the constant-voltage system, at an equal power load. 



It is seen from this example that unless synchronous 

 motors are thought to introduce an element of complica- 

 tion and unreliability into a transmission system, there 

 would be no advantage gained by producing a voltage 

 regulator which could operate with larger variations in 

 generator voltage than those used at present. 



This example deals with a line of medium length, 

 which would not have a troublesome amount of charging 

 current, and yet synchronous phase modifiers are seen to 

 be economical. It is sometimes stated that synchronous 

 phase modifiers are used with long transmission lines 

 because of difficulties caused by charging current, but 

 this statement is not correct, even where the charging 

 current produces a rise at no load equal to 10 or 15 

 per cent of normal voltage. Phase modifiers are to be 

 used with long lines chiefly because they save dollars 

 and cents, largely by saving line costs, and also, as in 

 this chapter, by increasing the efficiency of trans- 

 mission and the power-factor at the generators. The 

 savings are greater with very long lines because line 

 costs are then more prominent, and not because the 

 charging current is greater. In fact, for a given line, 

 the lower the voltage, the less will be the charging 

 current, and yet the greater will be the financial neces- 

 sity for phase modifiers. It will be shown in Chapter 

 XIII that the difficulties due to the charging current are 

 probably not equal to the advantages which it gives. 



