ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
232. 
1,000 amperes per square inch and the space factor as- 
., . sumed at .4, ealeulate the approximate necessary winding 
space on one side of the excitation coil. 
Assuming a maximum allowable winding depth of 1.75 
inches, caleulate the approximate useful pole height and 
_ fix it afterward definitely at d= 5 inches. 
Make the pole shoe height c = 1.20 inches, and collect the 
principal established dimensions of this alternator in a 
manner similar to that of the previous design in the form 
-. of a table. 
233. 
236. 
sy 
As a first approximation, calculate the air gap value by 
means of Equation 21 of the Instruction Book, assuming 
_ that about 70% of the field ampere turns are consumed in 
the air and allowing a reduction of the air gap of about 20 
per cent. on account of the effective iron section being re- 
duced by the slot openings, which consideration is entirely 
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 above. 
Caleulate 4 points of the no-load characteristic for 2,000, 
2,800, 3,300 and 3,800 volts and collect the different data 
in tabular form, similar to that given in the preceding 
design. The different path lengths which must be known 
are to be taken from a full-sized sketch, or may be 
calculated. ; : 
By means of Equation 29 of the Instruction Book, calculate 
the short-circuit constant for this alternator, determining 
first the reluctance of the armature leakage path. For this 
purpose take the projecting-out part of the armature 
winding 21, = 11 inches. 
By means of Equation 15 of the Instruction Book, calculate — 
the amount of field ampere turns per’ pole which corre- 
_ sponds to the normal short-circuit current of the armature. 
