ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 51 
may be driven higher than that stated in the curves, Figs. 
26 and 27. 
91. Iron Losses of Standard Generators.—The total iron 
losses of modern standard generators are given in terms of 
the machine capacity in Fig. 28, which, when compared 
with the curve in Fig. 14, will confirm the statement, that 
the armature iron loss is about 0.8 to 1.2 watts per |b. 
Table 10 gives the usual limit values of iron losses. 
TABLE 10.—USUAL LIMITS OF IRON LOSSES FOR 
DIFFERENT SIZES OF ALTERNATORS. 
Output of Alternator. Usual Limits in Per Cent. 
10 KVA 2.30 to 4.40 
BO. #5 1.90 ** 350 
sory. 1.60 ‘* 3.00 
200 = * 120 ‘* 2.50 
800. = ** 2:15 “** 2.15 
400 a 1.10 ‘* 2.00 
500 “i 1.00 ** 1.90 
750 * 85 ** 1.75 
1,000 oe GS. 20:45 
The curves in Fig. 29. indicate the hysteresis and the eddy 
current losses in terms of the magnetic densities. The eday 
current losses are given for two gauges of sheet iron. All 
the curves are based on a frequency of 100 cycles and the 
loss may be ealeulated for any other periodicity, by re- 
membering that the hysteresis loss is directly proportional 
to the number of cycles and the eddy current loss propor- 
tional to the square of the frequency. 
92. Example 10.—For one pound of laminated iron, the 
hysteresis loss at 100 eycles and an induction of 80,000, is 
equal to 10 watts. What is the loss under the same condi- 
tions at 40 periods? 
Solution: According to Par. 91, the loss will be 
7 10 x 40 
| 100 = 4 watts. Ans. 
