ADVANTAGES AND DISADVANTAGES 



29 



proportion is installed equal to 63 per cent of the load 

 kilowatts, not only is constant voltage maintained, but 

 the kilowatt capacity of the line is multiplied by 2^, 

 the efficiency of the line being lowered to 85 per cent. 

 This is summarized in the following table. Trans- 

 mission line data: Length, 100 miles; No. oooo copper 

 cables; lo-ft. spacing, 100,000 volts, 60 cycles. 



Of the investment in power transmission projects, 

 line costs form an important part, which increases as the 

 distance of transmission becomes greater. Accordingly, 

 it is found necessary with long distances to reduce the 

 line costs by using higher voltages, although this in- 

 creases the cost of transformers, circuit breakers, and 

 substations. An economic balance is found in practice 

 by adopting a voltage of approximately 1,000 volts per 

 mile. A similar reduction in line costs may be made 

 by installing synchronous phase modifiers and adopting 

 the constant-voltage method of control. The adoption 

 of this method may be equivalent, in reducing the cost 

 of the transmission lines for a given amount of power, 

 to raising the voltage approximately 50 per cent. 



The phase modifiers will be most applicable where 

 the voltage cannot be increased. The most common 



