136 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
per cent. on account of the paper insulation between the 
laminations and 4 inch for a ventilating duct, making 
the overall armature length equal to 10 inches. | 
235. Height of Core Above Slots.—The height of the 
armature core above.the slots in the present machine, is 
equal to 8.45 inches and the section 8.45 X 9.5 x 0.9 = 72 
square inches. 
The magnetic density is somewhat lower than the average 
4.12 10° 
2X 2 
value indicated in Fig. 26, caleulating out at 
= 28,600 lines per square inch. 
The low value of the density and the increased height of the 
armature core above the slots, is due to the fact that the 
same stamping, which is a standard size, is used for 
generators with a smaller number of poles and a larger 
flux per pole. 
236. Calculated Iron Loss.—-The loss per lb. of iron is 1.075 
watts, taking both the hysteresis as well as the eddy 
currents into account. 
237. Calculation of Open Circuit Characteristic.—The 
calculation of the open circuit characteristic is the next 
step. After having decided that the dimensions of the . 
armature are not subject to any radical criticism, the 
caleulated no-load curve should then be compared with the 
test results, to enable the calculation of the field turns 
and the determination of the short circuit characteristic 
to be carried out. The different load conditions, with the 
corresponding regulation, may then be discussed later 
with the different losses and efficiencies. 
238. Calculated Leakage Factor.—tThe determination of 
the flux in the field system is made in the first instance 
and therefore the leakage factor has to be fixed. 
