48 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
lines per square inch section of the armature core as found 
in modern commercial designs. 
TABLE 9.—UOSUAL LIMITS OF ARMATURE CORE 
DENSITIES FOR DIFFERENT FREQUENCIES. 
Frequency. Usual Limits in Lines Per Square Inch. 
25 35,000 to 58,000 
30 33,000 ‘‘ 55,000 
40 29,500 ‘* 48,500 
50 26,000 ‘* 43.500 
60 23,000 ‘* 39,000 
7 20,500 ‘* 35,500 
80 18,500 ** 32,000 
90 16,000 ‘** 29,000 
100 15,000 ‘* 27,000 
110 14,000 ‘* 25,000 
120 13,000 ‘* 24,000 
Fig. 26 gives the average values of densities in terms of the 
frequencies. This curve refers to the iron section below 
= 
ag 70 20 30 40 $0 £60 Yo 80 90 .100 #10 420 
NUYURER OF FREQUENCIES PER SECOAT. 
Fie. 26. —AVERAGE ARMATURE CORE DENSITIES FOR DIFFERENT 
FREQUENCIES. 
DENSITIES LW LINES PER SQUARE INCH 
& 
$ 
the teeth. The permissible number of magnetic lines per 
unit section of the teeth is indicated in Fig. 27. On re- 
ferring to Figs. 26 and 27 it will be noticed that the den- 
