ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 147 
and for half load eurrent, namely, 33 am- 
eee ey Eee. a 1,300 watts; 
the excitation energy of the field coils, when 
the armature carries a cos PY =.8 lagging 
eurrent of 66 amperes, equals.......... 5,150 watts; 
and for a cos P —.8 lagging current of 33 
MON Re Nigro Goat cha VI SK «48 tenses + + 20,400 Watts; 
The total losses for cos P= .8 inductive full load are equal 
to 7,000 + 8,600 + 5,200 + 5,150 = 25,950 watts. 
265. Efficiency. 
will be 
The efficiency at full load, with eos p = .8, 
400,000 
425,95U 
On half load, the total energy loss is 20,350 watts; conse- 
quently the half load efficiency is equal to 
200,000 ~ 
220,350 91%, 
The efficiency at full load, and in particular at half load, 
is slightly better than the usual efficiency of a standard 
machine, see Table 1. The reason for this is, that in this 
particular alternator, the weight of armature copper is 
somewhat more than usual and this variable loss item 
improves the half load efficiency. 
= 94%. 
266. Total Weight of Copper.—tThe weights of material 
used in this particular machine are as follows: 
Armature copper ........... 520 Ibs. 
Bt CODDOD © a sicce cbc deen ae aia 
Total copper used .......... 1,200 > * 
‘ which is less than that of a standard speed 400 KVA. 
alternator. 
This difference is due to the comparatively small number 
of field ampere turns, which produces a higher voltage 
drop than the average value. 
