398 ELECTRICAL ENGINEERING 



The loss in the line is 



and the resistance of each conductor is 



PP 

 100 nl 2 



For the same voltage E between conductors the current is 

 1 = ' single phase ' 



, three phase, 



VSEcosO' 

 and the resistance per conductor is 



pP X E 2 cos 2 6 pE 2 cos 2 . 

 r= iQQ x 2 pz = ' 005 ~~p > single phase, 



pP X 4 E 2 cos 2 e pE 2 cos 2 . 

 T = 100 X4P 2 = ' 01 P ' tw Phase ' 



pPXZE 2 cos 2 (9 p# 2 cos 2 . 



100 X3P 2 -P ' three Phase * 



Since the single-phase line has only two conductors while the 

 two-phase line has four the amount of copper required for both is 

 the same. The_three-phase line consists of three conductors of the 

 same section as the two-phase conductors and, therefore, the 

 amount of copper required for a three-phase line is only 75 per cent 

 of that required for a two-phase or single-phase line with the same 

 per cent power loss and the same maximum voltage between lines. 



256. Reactance. The inductance of a line per mile of con- 

 ductor is 



L = 0.074 -I- 0.0805 logio- 3 henrys, 



where D is the distance between conductors 

 and R is the radius of the conductors. 



The reactance of the line per mile of conductors is 



X = 2 TT/L ohms. 



The reactance could be decreased by decreasing the distance 

 between the conductors or by increasing the radius, but these 



