INDUCTION MOTORS 69 



(b) Plot the distribution of magnetomotive force in the air-gap 

 at one-eighth of a period later than in (a). 



(c) Plot the distribution of the magnetomotive force in the 

 air-gap at one-quarter of a period later than in (a). 



3. A 3-phase induction motor has a stator with 2 slots per 

 pole per phase. There are 4 inductors in series per slot. The 

 coil pitch is 6 slots. The effective value of the current in each 

 phase of the stator winding is 7.07 amperes, and the current 

 in phase two lags behind the current in phase one by 120 elec- 

 trical degrees and leads the current in phase three by the same 

 amount. Place the first slot in phase one at the extreme left 

 of the paper and draw the zero lines to allow for a maximum 

 ordinate of 2 in. Use the following scales in those plots: 



Absciss . Pole pitch = 3 in. 



Ordinal es. . . .40 ampere turns = 1 in. 



(a) Plot the distribution of the magnetomotive force in the 

 air-gap due to the stator currents at the time that the current in 

 phase one is a maximum. 



(b) Plot the distribution of the magnetomotive force in the 

 air-gap at one-eighth of a period later than in (a). 



(c) Plot the distribution of the magnetomotive force in the 

 air-gap at one-quarter of a period later than in (a). 



4. A 3-phase induction motor has a stator with 4 slots per pole 

 per phase. There are 4 inductors in series per slot. The coil 

 pi teh is 12 slots. The effective value of the current in each 

 phase of the stator winding is 7.07 amperes, and the current in 

 phase two lags behind the current in phase one by 120 electrical 



's and leads the e in rnt in phase three by the same amount. 

 Place the first slot in phase one at the extreme left of the pa per 

 :nnl <lra\v the zero lines to allow for a maximum ordinate of 

 1 in. I'M- the following >rale> in these plots: 



Pole pitch .'J in. 

 in .niiprn- turns 1 in. 



(a) Plot the distribution o! the magnetomotive force in the an - 

 .hie to the stator currents at the time that the current in pha-e 

 one is a maximum. 



Plot the li-trilnition of the magnetomotive force in tin- 

 air-gap at one-eighth of a period later than in (a). 



