- ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 9 
15. 
16. 
1%, 
18. 
19. 
The voltage drop is specified as the alteration or decrease, 
as the case may be, of the armature pressure, when the full 
load is switched on the fully excited generator, speed and 
excitation remaining constant. 
Slots Per Pole.—To procure a practically sinusoidal 
wave form of the current, the application of six slots per 
pole will be found a good average figure. 
Temperature Rise.—The average rise of temperature 
above that of the surrounding air, of any part of the 
machine, should not exceed the following values after a 
run of six hours at full load: The armature winding, 
75°F. rise; the field coils, 65°F. rise. On all other parts 
_ of the machine, the permissible temperature rise is 75°F., 
all temperatures to be measured by means of a ther- 
mometer. 
Short Circuit Current.—The alternator should not have 
a greater short circuit current than about three times the 
normal current, when the excitation corresponds to the 
normal open circuit voltage for the normal speed. For 
the definition of short circuit current see Pars. 117 
and 118. 
Insulation Test.—The insulation of the armature coils 
should be able to withstand double the normal voltage, and 
the field coils five times the normal voltage, for five 
minutes. 
Space.—As regards mechanical features, the generator 
should take up as small a space as possible, the construc- 
tion should be rigid and must offer every facility for 
repairs and give assurance against accident. 
Effect of Altering the Design.—Supposing that the 
design of a generator is in every respect satisfactory and 
