84 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. | 
The revolving, alternate pole type generator will be dis- 
cussed, because it is the most modern type of machine; but 
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Fie. 42.—SYMBOLS OF THE DIMENSIONS OF THE MAGNETIC PATH. 
it should be noted that the expressions may also be applied 
to the revolving armature type alternator. 
In the following calculations the magnetic resistance of only 
one pole is dealt with. 
142. Magnetic Reluctance of the Field System.—The 
magnetomotive force of one magnet coil forces a certain 
number of lines through the rim of the wheel, the pole 
core and the pole shoes. The reluctance of the pole shoes 
is in most cases too small to take into account, so we write 
for the reluctance of the pole system: 
d e 
r, = 0.818 x [— Woh PIPE = |--- a9) 
For the definition of the various symbols see Fig. 42. 
Further “,; = the permeability of the iron in the wheel 
rim, and 
Mp = the permeability of the iron in the pole 
core; both these values vary with the 
degree of saturation, 
