ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 41 
centage of the input, shall be nearly constant throughout 
a big range of the external load. In this case it is obvious 
that the constant losses are to be kept low and the variable 
losses may be taken somewhat higher. The required con- 
dition is obtained, without any considerable sacrifice in 
the commercial design, by increasing the current density 
in the armature conductors slightly more than usual. 
100 — SD 
“ EE 
\, 40 40 
8 nt Ay Sen esis R 
RU . 
‘ 4 
st 
N oft > a a ; 
N N 
: “Li PRET ION ZATION | SRE BPRS 
as c 40 
J a ee 22 
tt a 0 
° 209 400 600 800 000 7200 F400 1600 4800 2000 
OWTKUT IN KVA. 
Fie. 24.—Trst Curves SHowina Losses AND EFFICIENCY OF A 1,600 
KVA., 450 Revs , 45 CycLte, THREE PHASE ALTERNATOR. 
The test curves, Fig. 24, show distinctly, which losses 
belong to the respective classes. 
77. Constant Losses.—The friction and iron losses are 
strictly constant, the energy required for the excitation 
is an item which contributes to the constant as well as 
to the variable losses. On the other hand, the armature 
copper loss is a strictly variable one and its curve in 
