116 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
_ 
and iron sources as regards commercial regulation, as weil 
as the most economical distribution of material. 
If a higher voltage drop than reasonable is permitted, then 
the total flux may be less than that indicated in Fig. 62. 
188. Example 25.—A 300 KVA. alternator, running at a 
speed of 100 r.p.m. and generating an E.M.F. at 50 cycles, 
should, for the normal voltage, have a total flux corre- 
ye Oe KVA. ait eh 
sponding toro = Sao NW? that is, it has to be about — 
100 x 10° lines. The number of poles being 60, a useful 
0 é 
flux per pole of - x 10° = 1.66 X 10° will be required 
if a reasonable voltage drop and an economical design is 
desirable. 
‘As another illustration, take a 400 KVA., 60 cycles, 600 
r.p.m. machine : 
. . KVA. 400 
In this case the ratio NW 6007> 0.666, and the corre- 
sponding flux value is F, X 2p=52%X10* lines; or 
2 ~ 10° j 
ali sae = : = 4.33 x 10° lines per pole. 
189. Reliable Data for Alternator Design.—The data 
of Fig. 62, together with the fundamental Equation ($3), 
offer the best and most reliable basis for a successful 
alternator design, which can be further assisted by proper 
and skilful ealeulation of the details. In Par. 165, the 
fundamental equation has been given in the form: 
This can be advantageously written in another form, by 
multiplying both sides of the equation with the number 
of phases m and with the normal current in amperes, from 
which, 
