WORKING METHODS OF CALCULATION 77 



For more accurate work, any point on the diagram may 

 be directly calculated by the methods in Tables I-IV. 



Instructions for drawing the circle diagram of a 

 constant- voltage line are given in (i), Table I, when the 

 load is specified at the receiver end. An ordinate to the 

 circle represents the reactive Kva. in the line at the 

 receiver end, for an amount of delivered power in kilo- 

 watts represented by the corresponding abscissa. An 

 ordinate to the straight line represents the reactive Kva. 

 of the load, and an ordinate to the ellipse shows the 

 reactive Kva. of the synchronous motors. Reactive 

 Kva. as shown on the diagram are leading when the 

 ordinate is positive and lagging when it is negative. 

 See Fig. 10, which shows the circle diagram for the line 

 in Example i, Chapter X. 



The straight line is most easily drawn by plotting an 

 abscissa, cos 0, and an ordinate, sin 9, to give one 

 point on the line. The ordinates of the straight line 

 must be added to those of the circle, because the syn- 

 chronous motors must correct the lagging Kva. of the 

 load, as well as provide the reactive Kva. in the line at 

 the receiver end. 



The theoretical limit of the load of a line may be 

 read directly from the circle diagram, or it may be cal- 

 culated by formula (2) . This theoretical limit is so much 

 larger than the regular load of an ordinary line with 

 rather small conductors, as about No. ooo, that it is of 

 little importance in such cases. It is of considerable 

 importance, however, with conductors as large as 

 350,000 circ. mil copper, since the efficiency is high right 

 up to the theoretical limit. The addition of reactance 

 directly decreases the theoretical limit. In practice, the 



