2 3 8 



ALTERNATING CURRENTS 



which results from the vectorial addition of the e.m.f.'s of consecutive 

 coils, becomes indistinguishable from a circular arc. Hence, in order 

 to find the voltage relations on the continuous- and alternating- 

 current sides, we may adopt the following construction. On a line 

 OP (Fig. 149) as diameter the length of OP representing, to a 

 suitable scale, the voltage between two consecutive brushes describe 



FIG. 148. Polygon Construction for 

 Resultant c.m.f. 



FIG. 149. Construction for Voltage 

 Eatio in Kotary Converter. 



the semicircle OSQP. If the distance between the points of con- 

 nection of two given slip-rings is -^th of Jhe pole-pitch, then, in order 



to find the maximum value of the alternating voltage between the 

 slip-rings, lay off from the centre E of the semicircle a line EQ such 



that the angle OEQ = -^ in circular measure, or =- in degree measure. 

 Join OQ ; then OQ gives the required maximum value of the alter- 

 nating voltage. The r.m.s. value of this voltage is given by -p=, but 



V 2 



