TRANSMISSION LINES. 349 



From these data we find : 

 /= 58.8 amperes. 

 r' = 5 1 ohms. 



Therefore, from the table we find that, approximately, a No. 2 

 B & S. wire is required so that x= 37.7 ohms. 

 Furthermore, 



E l cos 6 = 1 7,000 volts. 



E l sin 6 + xl = 12,700 volts, 

 and from equation (i) we find 



r == 37.3 ohms. 



from which the correct size of wire is found to be, approximately, 

 a No. i B. & S. 



160, Calculation of double line for two-phase transmission (four 

 wires). In this case each line is calculated to deliver half the 

 prescribed power. Thus, if it is desired to deliver 1,000 kilo- 

 watts at 20,000 volts two-phase, at a frequency of 60, line drop 

 of 3,000 volts, etc., then each line is calculated as a single-phase 

 line to deliver 500 kilowatts at 3,000 volts line drop. 



161. Calculation of a three-wire transmission line for three- 

 phase currents. The calculation will be carried out for the case 

 in which both the generator and the receiver are Y-connected as 



shown in Fig. 298. If it 



^ener^ ___ recc/ver ^ ^ ^.^ ^ ^^ ^ 



\& ^ problem by specifying 



the voltage between mains 

 at generator and at re- 

 ceiver and current in each 



main, the specified volt- 

 age between mains may be divided by 1/3 to give the values of 

 E and E l (see Fig. 298). 



Let cos be the power factor of each receiving circuit, P 

 the total power to be delivered, E l the electromotive force be- 

 tween the terminals of each receiving circuit, and E Q the elec- 

 tromotive force of each armature winding on the generator ; all 



