210 



ARMATURE CONSTRUCTION 



TABLE XVI. 



PROPERTIES OF WINDING IN FIG. 241 CONNECTED AS TWO- AND 



THREE-PHASE. 



This matter of the applicability of a single winding to both 

 two -phase and three-phase is of considerable interest, as it 

 determines the number of slots permissible for armatures to be 

 used for both two- and three-phase with two-range windings. 



2. The condition for any two-range winding to be either two 

 or three-phase is simply that the total number of coils must be a 

 multiple of 6 (2 x 3). 



From this follow directly the numbers of slots which may 

 be used with such armatures. A single coil cannot occupy less 

 than two slots, one on each side ; and as the minimum number of 

 coils must be six, the minimum number of slots is 6 X 2 = 12. 



3. Any permissible number of slots must be a multiple of 12 

 thus 12, 24, 36, 48, 60, and 72, etc., are the possible numbers of 

 slots to be used for armatures capable of being wound with both 

 two and three-phase two-range windings. 



In such a winding the number of poles equals the number of 

 coils per phase when connected for two-phase, and twice the 

 number of coils per phase when connected for three-phase; the 

 latter winding is half-coiled and the former is not. (See also 

 p. 191 as to the conditions under which a three-phase winding 

 can be laid up in two ranges.) 



