234 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



The use of fractional pitch windings and fractional-slot connec- 

 tions, will reduce some of the harmonics; but as commutation limits 

 the pitch reduction to a comparatively small range, only the higher 

 harmonics are affected. 



If the voltage ratio could be under control by a pure third har- 

 monic in the flux distribution curve, the resulting third harmonic in 

 the phase E.M.F. could be eliminated from the line voltage by con- 

 necting the transformer primaries in star. 



TWO-PART POLE 



This gives unsymmetrical distortion, and a lateral shifting of the 

 flux distribution curve; i.e., the q h 's are no longer zero, particularly 



FIG. 33. 



qi>\. Thus q\ = \/i+qt,i 2 is no longer unity, and KJ is changed by q\ 

 as well as by K g . If these changes are in the same direction, the 

 harmonics in the tap E.M.F. will be obviously less for a given dis- 

 tortion. 



In an actual machine for which the flux distribution curve is 

 shown in Fig. 33, the voltage was 



O.862 = /J )<Q fi 



I.2QS 



less than two-thirds of the ratio for a sinusoidal flux distribution 

 curve, and just about two-thirds of that for a normal undistorted 



