ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. ad | 
185. 
186. 
187. 
1 88. 
189. 
190. 
191. 
192. 
Make the poleshoe height ¢ = 1 inch and collect the prin- 
cipal, established dimensions of this machine, in a manner 
similar to that shown in Par. 314 of the Instruction Book. 
A dimensioned sketch similar to Fig. 74 of the Instruction 
Book is also to be given. 
By means of Equation 21 of the Instruction Book as a 
first approximation, calculate the air gap value, assuming 
that about 70% of the normal field ampere turns are 
consumed in the air and allowing a reduction of the air gap 
of 10% on account of the effective iron section being 
reduced by the slot openings, which consideration is en- 
tirely neglected by the application of Equation 21. 
By means of Equation 26 of the Instruction Book, calculate 
the leakage factor of this alternator and see whether the 
value so obtained is in accordance with the one previously 
assumed. 
Calculate four points of the no-load characteristic for 600, 
800, 1,000 and 1,200 volts and collect the different data 
in table form similar to Table 19 of the Instruction Book. 
The different path lengths are to be taken from a full 
sized sketch, or may be calculated. 
By means of Equation 29 of the Instruction Book, caleulate 
the short-circuit constant for this alternator, determining 
first the reluctance of the armature leakage path r,’. For 
this purpose take the projecting out part of the armature 
winding 21, = 7 inches. 
By means of Equation 15 of the Instruction Book, calculate 
the ameunt of field ampere turns per pole which corre- 
sponds to the normal short circuit current of the armature. 
Plot the no-load and short circuit characteristics, applying 
the following seales: 1,000 ampere-turns = 1 inch; 250 
volts terminal pressure =1 inch; 75 amperes armature 
current = 1 inch. 
In the same. figure determine graphically the voltage drop 
