THE ROTARY CONVERTER. 315 



The virtual voltage of a closed circuit armature giving 

 alternating current is (see page 194.) 



60 x 10 8 v *JT 



assuming the wave form to be a sine curve, as is usually 

 approximately the case with a distributed winding. 



Hence, if we neglect the losses in the armature con- 

 ductors, the ratio of direct to virtual alternating single- 

 phase voltage is 1 : -73=-, i-e., 1 : *707. 



\/ u 



Thus, if the rotary converter is supplied with 100 volts 

 direct current, it will give out 70*7 volts alternating. 

 If supplied with 100 volts alternating, it will give out 

 141*4 volts continuous current. In either case, the 

 maximum value, of the alternating voltage is the same as 

 the voltage of the direct supply, and the virtual value is 

 the maximum value -*- y% ^ the wave form of the 

 alternating current is a sine curve. 



The ratio of direct to alternating current is the inverse 

 of the ratio of the voltages. This follows from the fact 

 that the input and output watts must be equal (except for 

 the incidental losses in the machine), and hence, if we 

 postpone the consideration of the effect of lagging or 

 leading currents, 



Volts (direct) x amperes (direct) = volts (alternating) x 

 amperes (alternating). 



But it has just been shown that 



Volts (direct) = volts (alternating) x 1*414. 

 Hence, 



Volts (alternating) x 1*414 x amperes (direct) = volts 

 (alternating) x amperes (alternating) ; 

 Or, 



Amperes (alternating) = 1*414 x amperes direct, 



i.e., the (virtual) alternating current (with sine wave form) 

 is nearly 1 times the value of the direct current supplied 

 to, or taken from the commutator. 



Polyphase Rotary Converters. A single-phase two-pole 

 converter will have two slip rings connected to conductors 

 situated at opposite points on the armature. If the 

 machine has a number of poles, the slip rings will each 

 have as many connections to the conductors as there are 

 pairs of poles. The angular pitch between two successive 



