CALCULATION OF A SINGLE-PHASE CURRENT MOTOR. 



STARTING ARRANGEMENTS. 



128. A few words may fitly be added about the methods of starting 

 single-phase motors. It has generally been found advantageous to 

 use two-thirds of the pole-pitch for the main winding, and to leave 

 the remaining third for the starting phase. The motor thus starts 

 as an imperfect two-phase current motor. An external armature re- 



cb 



a 



S 



S 



5 











MM in 



AAA/WW 



FIG. 38. 



sistance is to be recommended for large sizes, say, for an output above 

 15 horse-power. 



129. The starting phase receives generally either half the number of 

 convolutions as the main phase, or twice as many. The latter method 

 seems to be preferable. Figs. 38 and 39 show the switch used by 

 the Oerlikon Engineering Works for their single-phase motors. 



