HIGH-TENSION NET- WORKS 53 



some arrangement could be made, such as utilizing the 

 economies of the constant-voltage system, whereby 

 transmission would be made profitable at 300 miles 

 instead of 150, then these stations could be connected 

 to form one net-work. At present, a high-tension net- 

 work covering a section of country often requires the 

 development of very small water-powers, so as to have 

 sources of energy supply at close enough intervals. But 

 with a constant-voltage net-work, with synchronous 

 motors holding the voltage steady at every substation, 

 the distance between generating stations may be much 

 greater, thus permitting the connection of existing trans- 

 mission-line systems, without the delay and risk of 

 building small intermediate power stations which might 

 be liable to be unprofitable, even with the advantages of 

 operation in a net-work described above. 



Thus the principles of constant- voltage transmission 

 can influence very strongly the rate of growth and the 

 profitableness of large transmission line net- works, and 

 may make it immediately commercially practicable to 

 connect any number of power systems into one large 

 net-work of transcontinental extent. 



The possible ultimate size of a high-tension net-work 

 will probably not be limited by the danger of having 

 practically unlimited generating capacity connected to 

 one electrical system when a short circuit occurs. The 

 reason is that a short circuit in a net- work extending some 

 hundreds of miles, as the largest modern net-works do, 

 cannot seriously affect distant portions of the net- work, 

 owing to the impedance of the intervening lines. Thus 

 when a short circuit occurs the voltage gradient along 

 the lines is steep, and current is supplied to the short 



