ALTERNATING ‘GENERATORS AND SYNCHRONOUS MOTORS. 19 
For high tension alternators it is advisable to use open 
slots only and so far general practice approves the use 
of the open slot for all eases. 
The section of copper conductors and the choice of form 
is an important item, because upon it depends the econom- 
ical utilization of the winding space inside the slot. 
In works where standard stampings with certain slots are 
stocked, the designer is very often compelled to arrange 
the copper wires according to the slot form. It is often 
found advantageous to use two, three or more wires in 
OS 
S 
c* = 
pe 
ee 
iN a3 —_— Sar sns§ 
NI} re ee 900 ie eT 
CR 
O4 
2 es ee 
4000 =2000 3000 4000 Sv00 6000 O00 foc0ee 
THESE PRESSURE LW VOLTS. 
Fig. 9.—AVERAGE Stot Space Factor FoR Four DIFFERENT 
S1zEs oF ALTERNATORS. 
parallel, instead of a single thick wire, in order to fill the 
slot neatly. 
38. Space Factor.—Fig. 9 gives the average values of space 
factor for different voltages and sizes of machines. The 
space factor is defined as the ratio between the copper 
section inside the slot and the air section of the slot. 
39. Shape of Conductors.—For large current machines, the 
following conditions are to be taken into consideration 
in choosing the armature conductors: A conductor of 
large section is hable to produce eddy currents which 
