214 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
insulation between the turns of a coil or between the coils 
themselves, which short circuits the copper, and faulty 
insulation of the windings to the iron, or earth. - 
416. Terminals and Slip Rings.—If the necessary eare is 
taken, there will\be very little trouble with the terminals, 
and up to about 1,000 volts, marble terminal boards will 
be found satisfactory, while for higher voltages insulators 
of proper form and arrangement should be used. 
The slip rings seldom cause any trouble, but it is advisable 
to employ at least two sets of brushes of ample section, so 
that if one goes wrong the other should be able to carry 
the full current. 
orate 
60°} 60° 
Fie. 91.—TuHreE-PHase ArmA- Fia. 92.—THREE-PHASE ARMA- 
TURE WINDING PROPERLY TURE WINDING WRONGLY 
CONNECTED. CONNECTED. 
41%. Field Coils.—It should be noted that the field coils some- 
times heat up; this is due in most eases to too much taping 
and wrapping. 
If the field coils project out of the pole shoe strong end 
plates should be used in order to prevent the coils bending 
upward on aceount of the centrifugal forces. 
120°; 720° 
—_ ee 
418. Connection of Three Phase Armature.—In con- 
necting the different phase windings of a three phase alter- 
nator, it is necessary to see that the coils are properly 
joined up at their ends, which should be 120 degrees 
apart in the pole pitch, as an armature with the coils con- 
nected 60 degrees apart will not generate the full voltage, 
see Figs. 91 and 92, 
Printed in U.8.A., 
