320 



armature winding is a distributed one, and consequently 

 does not influence the form of the wave. The width of 

 the poles is consequently the chief factor in modifying 

 the wave form produced, and its effect is usually stated 

 in terms of the ratio of the width of pole to the pitch of 

 the poles (i.e., the distance from centre to centre of the 

 poles). 



This ratio consequently largely determines the virtual 

 value of the alternating voltage (its maximum value is 



O 



-1 



1-1 1-2 



3 -4 -5 -6 -7 -8 "9 VO 

 Amperes Excitation, Curves I. and II. 

 O 1O 2O 3O 4O 5O 6O 7O 8O 9O 1OO 11O 12O 



Direct-current Volts, Curve III. 

 FIG. 159. NO-LOAD CHARACTERISTIC OF ROTARY CONVERTER. 



determined by the direct-current voltage) and the ratio of 

 transformation of a rotary converter. The following 

 table shows the influence of the pole width upon the ratio 

 of transformation of a single-phase rotary converter. In a 

 polyphase converter the ratio of transformation is 

 altered in the same proportion by change in polar length. 



In the case for which the curve, Fig. 159, was drawn, 

 the polar arc was rather more than '75 of the pole pitch, 



