TIIK INDUCTION MOTOR 



233 



3-Fbaie Supply 



time-degrees. Positions (3), (4) and (5) are taken at time-degrees 

 90, 135, and 180 of the two currents. Between points (1) and (5), 

 tat ing field has advanced only 90 space-degrees, whereas 

 the currents have passed through 180 time-degrees. Therefore, 

 the speed of this rotating field in revolutions per second is one- 

 half the frequency of the supply in cycles per second. 



The N- and S-poles which are produced by the stator rotate 

 in the air gap and cut the rotor or armature conductors, in- 

 ducing currents in them. These currents, reacting with these 

 stator poles, produce rotation 

 of the armature, just as in 

 Fig. 217, the induced currents 

 in the disc and the flux pro- 

 ducing them react and cause 

 the disc to rotate. 



Figure 225 shows a single- 

 layer, three-phase, four-pole, 

 lap winding adapted to a 

 machine having nine slots per 

 pole or three slots per pole 

 per phase. This winding is 



Very similar to that of Fig. FIG. 225. Single-layer, 4-pole, 3-phase, 



223 and is used in the in- induction motor winding; hip-mim,-. t,,i 

 duct ion motor shown in Fig. 226. For simplicity, but one phase, 

 shown connected, the other two phases, B and C, being 

 connected in a manner similar to A. 



Figure 226 shows four successive positions of the rotating field, 

 for corresponding values of the polyphase currents in the stator of 

 this three-phase induction motor. In (1) the current / , i> WTO, 

 so that I B and I c are opposite and equal. The position of the 

 field is shown at this instant. In (2) the currents I A and /,- 

 an- but half their maximum positive values and their positions 

 on the stator are such that their phase belts are on each side of 

 B-belt iii which the current is a maximum. The.refore. tin- 

 field is symmetrical at thi- position. 



It will be noted :d>o that the time-angle between SUCCCSSivC 



value.- of current in 1-2-3 is MO electrical-degrees, whereas the 

 field adv; t 15 space-degrees bet id (2) and also 



between (2) and (3). Between positions (1) and (1 



