20 
ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS, 
176. 
177. 
178. 
179. 
180. 
181. 
182. 
1835. 
184. 
a 
Assuming an average pole are ratio of = .60 and that 
about 10 per cent. of the total armature length is taken 
up by insulation paper, caleulate the overall length of 
the armature including a ventilation duct of .5 inch 
width. oe 
With reference to Fig. 26 of the Instruction Book, deter- 
mine the necessary effective armature core section and its 
height above the slot. 
Assuming a pole core density of 105,000 lines per square 
inch and an average leakage factor of © = 1.25, calculate 
the effective pole core section and the necessary pole 
width, taking into consideration that about 5 per cent. 
of the pole core length is taken up by insulation material. 
The magnetic density in the east iron rim should be about 
40,000 lines per square inch; calculate its necessary sec- 
tion accordingly. 
Determine the rim dimensions by allowing 2.75 inches 
projection on each side of the magnet pole for support 
and protection of the field coiis. 
By means of Equation 30 of the Instruction Book, eal- 
ealeulate the value of the effective back ampere turns. 
Caleulate the value of the necessary field ampere turns 
per pole corresponding to the normal open cireuit pres- 
sure, taking into consideration that, with regard to the 
specified voltage drop, the normal excitation ampere turns 
must be about 2.5 times greater than the normal effective 
back ampere turns. 
The current density in the field winding being chosen at 
1,100 amperes per square inch, and the space factor as- 
sumed at .4, calculate the approximate necessary winding 
space of an excitation coil, x 
Allowing a maximum winding depth of 1.5 inches, calculate 
the approximate useful pole height. 
