210 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
' THE COOLING SURFACE OF ARMATURE: 
Dx eXT+ DX x xt- SF ag +2) ae 
THE TEMPERATURE RISE ON STATIONARY ARMATURE: 
T = %5 Wart: Wes 
2 O, 
THE EFFICIENCY OF THE ALTERNATOR: 
i KVA 
t= KVA+ W.+ Wi + We tee 
PRACTICAL WORKING OF ALTERNATORS. 
405. Paralleling.—In Book 37, pages 17 to 37, the subject of 
paralleling is fully dealt with, but the following remarks 
will be of interest, as they concern the design of the 
generators. 
406. Rise in Terminal Voltage.—If an alternator is 
switched on a line possessing considerable condenser effect, 
the terminal voltage will rise considerably, due to the 
combined effects of the inductance of the generator arma- 
ture and of the capacity of the line. 
In some eases the voltage will rise to such a value that it 
becomes disastrous to the machine as well as to the line. — 
This effect generally happens with alternators which have 
a wave form differing from the sinusoidal form, as the 
harmonies of the higher periodicity come into play. 
With the view of a possible voltage rise, it is necessary to 
design the insulation with an ample factor of safety, or 
if such voltage rise is anticipated and its prevention is 
necessary, it is found desirable to design the alternator 
with a large number of slots, as well as with rounded and 
shaped poles, so as to approach the, sinusoidal wave form 
~ as closely as possible. 
