ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 43 
Solution: Referring to curves, Fig. 24, the iron losses 
are 35 K.W. as before; the excitation loss is 4 K.W.; 
the armature copper losses are 2.9 K.W.; the friction 
and ventilation losses remain the same as before, namely, 
13 K.W. These make a half load efficiency of 
8090 
Saree pase is ~ 8885: 
that is, 93.5% of the input, will be delivered as useful 
output. Ans. 
81. Grouping of Losses.—The grouping of the different 
losses in their respective classes, expressed’ in percentage 
of the input, will be instructive and found useful, for 
the preliminary calculation of the efficiency on different 
loads. 
On Full Load: On the fully loaded generator the input 
is 1,600 + 0.96 = 1,666 K. W., and the iron loss is 2.1% 
35 
of same, because —— 1,606 ~ = 0,021. 
In the same manner, the friction and ventilation losses 
represent 0.78%; the excitation energy is 0.3% of the 
total input; and the armature current contributes 0.7% 
to the losses. 
Consequently the fully loaded generator develops 2.88, say, 
2.9% constant losses, 0.7 variable losses; and 0.3% of 
the input is utilized for the excitation. 
On Half Load: On half load the input is 800 + 0.935 
= 855 K. W. The constant losses give for the half load 
1 
input, a percentage of ei : = 5.65%, composed of 4.1% 
vu 
iron and 1.55% friction losses, which are double that 
of the corresponding figures for full load. The variable 
energy consumption in the armature copper, in percent- 
age of the half load input, is somewhat less than one half 
of the corresponding percentage on normal output. The 
excitation energy adds 0.47% to the losses. 
