ROTARY CONVERTERS 95 



alternating-current voltage to the direct-current voltage. As- 

 sume that the coil pitch is one and that the phase spread is 

 one-sixth. 



21. The graph representing the flux distribution in the air- 

 gap of a rotary converter is B = Bisinx B 3 sin 3x. x is the 

 angular displacement measured from the neutral point. Take 

 the third harmonic component of the flux density as 0.3 of the 

 fundamental. Assume that the armature winding is uniformly 

 distributed. Calculate the ratio of the single-phase alternating- 

 current voltage to the direct-current voltage. Assume that the 

 coil pitch and the phase spread are each unity. 



22. In problem 21 calculate the ratio of the four-phase alter- 

 nating-current voltage to the direct-current voltage. Assume 

 that the coil pitch is one and that the phase spread is one-half. 



23. In problem 21 calculate the ratio of the three-phase 

 alternating-current voltage to the direct-current voltage. As- 

 sume that the coil pitch is one and that the phase spread is 

 two-thirds. 



24. In problem 21 calculate the ratio of the six-phase alter- 

 nating-current voltage to the direct-current voltage. Assume 

 that the coil pitch is one and that the phase spread is one-third. 



25. In problem 21 calculate the ratio of the twelve-phase 

 alternating-current voltage to the direct-current voltage. As- 

 sume that the coil pitch is one and that the phase spread is one- 

 sixth. 



26. In a single-phase rotary converter, assume that the cur- 

 rents on the direct- and alternating- current sides are respectively 

 steady and sinusoidal, and neglect all of the losses in calculating 

 their relative values, (a) Calculate the ratio of the average 

 heating in a conductor at one of the alternating-current taps to 

 that in a conductor midway between the taps when the rotary 

 is operating at unit power factor, (b) Calculate this ratio 

 when the rotary is operating at 0.7 power factor. 



27. In a four-phase rotary converter assume that the run-rut- 

 on the direct- and alternating-current sides are respectively 

 steady and sinusoidal, and neglect all of the losses in calculating 

 th'ir relative values, (a) Calculate the ratio of the average 

 heating in a conductor at one of the alternating-current taps to 

 that in a conductor midway between the taps when the rotary 

 is operating at unit power factor, (b) Calculate this ratio 

 when the rotary is operating at 0.7 power factor. 



