TRANSMISSION OF POWER FOR SUBSTATIONS. 163 
found the following to be the most convenient and direct. 
Write in (1) }%:for C, and D, the distance between sta- 
tions, for I, ‘Then 
W 
i 
A% 
c.m, = — 
E‘ ’ 
E being as before the loss in volts, while W is watts de- 
livered and V voltage of delivery. 
Applying this formula to the example just given we 
have 
  
Pt X B0 106,060 
c.m =29 " 7N "D~ — 55 000. 
1000 
This is the area of each of the three wires. Similarly for 
the total weight we may modify (5) and multiply by 3, giv- 
ing for a close approximation the exceedingly simple form 
W 
100 — D 
  
W = 
R0 
K 
Applying this to the case in hand we have 
W — 100 50X 10,000 
1000 
= 50,000 lbs. 
These formule for alternating transmission circuits 
enable the economics of the matter to be investigated very 
rapidly. In the final design of the line it will usually be 
found, as in the case given, that the size of wire will fall be- 
tween two standard sizes. Inthis case, asarule, select the 
nearest size and figure out the final amount of copper from 
the actual weight of this wire, 
If the excitation of the motor or rotary converter 
fields is properly adjusted no account need be taken of in- 
ductive drop, since the widest departure of the power 
factor from unity will not in any practical case be great 
enough to disturb the working voltage seriously. 
The only time at which inductance is much in evi- 
dence is during the periods of starting the motors or ro- 
tary converters. For the best results the generators