10 



TRANSMISSION LINE FORMULAS 



formula for regulation, since the charging current is present 

 at both no load and full load. 



In selecting the spacing point on the chart, one notes 

 whether the frequency is 25 or 60 cycles, and whether the 

 conductor is of copper or aluminum. The spacing points 

 are the same for both solid wire and cable. When the 

 wires of a three-phase line are not spaced at the corners of 

 an equilateral triangle, but are at irregular distances a, b, 

 and c from each other, as in Figs. 5 and 6, the equivalent 

 spacing 



s 

 should be used. 



Fig. 5. Irregular Triangular Spacing. 



............ c ............ 



Fig. 6. Irregular Flat Spacing. 



r ..... ..... t ...... "-1 



l ............ 2a ............ j 



Fig. 7. Regular Flat Spacing. 



With regular flat spacing, as in Figs. 7 and 8, the equa- 

 tion for the equivalent spacing becomes simply 



s = 1.26 a. 



It makes no difference whether the plane of the wires 

 with flat spacing is horizontal, vertical or inclined. 



The spacing of a two-phase line is the average distance 

 between wires of the same phase. The distance between 

 wires of different phases is not considered. 



The points marked on the resistance scale at the right 

 of the chart are for cables at 20 C., assuming hard -drawn 

 copper of a conductivity equal to 97.3% of the Annealed 



