158 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. | 
and the two iron sections, one adjoining the pole shoe and 
the other the wheel rim, of 
64 X 2 xX 5.4 X 3.95 = 2,700 square inches, 
making a total for the 64 poles of 17,200 square inches. 
According to Equation (41) with a constant of 120, the 
temperature rise will be 
8,200 
17,200(1 +-0.0002 x 4,150) — Be 
120 x 
294. Full Load Efficiency.—For the determination of the 
efficiencies, we have now the following losses: 
The tron losse8.600. Sass ake see eee 9,700 watts. 
watts consumed in the armature winding... 8,200 ‘‘ 
excitation watts for cos Y= 08 full load... 8,200 ‘‘ 
and for the friction and ventilation losses 
we assume ........ oi. ¢ TERRE Ov bane | eee 
making a total of..............- wed tar 32,100 watts. 
The full load efficiency with a power factor of cos Pp = 0.8, 
‘ .000 
will be he 6 09 Sa. 
375,000 ++ 32,100 
295. Half Load Efficiency.—For half load, that is, when 
the armature winding carries 31.25 amperes, with a power 
factor of cos Pp — 0.8, the armature loss will be 2,050 
watts, and the excitation power 6,000 watts, while the iron 
and friction losses remain practically unaltered; conse- 
187,500 
187,500+-23, 750: 
quently the half load efficiency is equal to 
= 89 per cent. 
296. Relative Weights of Iron and Copper.—With | 
reference to the data of Table 14, it is interesting to 
compare the various weight items of low speed and 
standard alternators, of equal output. 
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