. Armour engineer. curve ofthe main. 68 THE ARMOUR ENGINEER [Vol. 2, No. 1 The fall in pressure or voltage up to any point is given by d= f i dr = fl(l ) dr (3) 0 ^0 R = I(r 2R (4) 4SO 40 480 30 1 I 460 /O j \ r. \£ 450 e\ 1 v .02 .04 .06 08 I RlBsafoncs - Ohms O JOOO 2O0O 3O0O 4000 .innO O/i-fiance - /vet 7779 Armour Eno*ie&- Fig. 2. The last expression (4) is the equation of the drop curveexpressed in terms of the two variables d (fall in pressure involts) and r (resistance in ohms), and represents a parabolapassing through the origin. Fig. 2 gives this curve. The pressure at any point is gi
. Armour engineer. curve ofthe main. 68 THE ARMOUR ENGINEER [Vol. 2, No. 1 The fall in pressure or voltage up to any point is given by d= f i dr = fl(l ) dr (3) 0 ^0 R = I(r 2R (4) 4SO 40 480 30 1 I 460 /O j \ r. \£ 450 e\ 1 v .02 .04 .06 08 I RlBsafoncs - Ohms O JOOO 2O0O 3O0O 4000 .innO O/i-fiance - /vet 7779 Armour Eno*ie&- Fig. 2. The last expression (4) is the equation of the drop curveexpressed in terms of the two variables d (fall in pressure involts) and r (resistance in ohms), and represents a parabolapassing through the origin. Fig. 2 gives this curve. The pressure at any point is given by (E—d) and may beplotted with the same abscissas as (4) and with ordinates ob-tained by subtracting the values d from the constant terminalpressure, E, as shown in Fig. 2. The i2r loss in the line is given by w = f i2 drJ 0 (5) Jan. 1910] MARSH : ELECTRIC DISTRIBUTING MAINS 69 r r = 12(1 )2dr ^0 R (6) = P(r + ) R 3R2 (7) If (7) is plotted in terms of the loss w and the resistance r,Fig. 3 is .ce .m .C6 oe .//tests/artce - Ohms O fCOO ZCOO 3COO 40DO SOOO The Armour B^ttec Fig. 3. The power in the line at any point isp = (B—d)i r2 r = [E —I(r )] (1 )I 2R R (8)(9) TO THE ARMOUR ENGINEER [Vol. 2. No. 1 r 3r2 r3 = I[ E(l ) — I(r + ) ] (10) R 2R 2R2 Equation (10) plotted in terms of p and r is shown in Fig. the process of plotting equations (8) and (10), thework may be shortened by ignoring the terms involving r3, asthey are small in comparison to the others and hence theiromission will not seriously affect the correctness of the curves.
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