384 



ELECTRICAL ENGINEERING 



converter will be the same as when operated as a direct-current 

 generator when the power factor is about 85 per cent and the 

 rating of a machine as a six-phase converter will be the same as 

 when operated as a direct-current generator when the power 

 factor is about 75 per cent. 



Rotary converters should, therefore, be operated at unity power 

 factor at full load and overload. 



241. Armature Reaction. The armature reaction of a rotary 

 converter is the resultant of the armature reactions of the machine 

 as a direct-current generator and as a synchronous motor. The 

 direct-current brushes are usually placed at right angles to the 

 field poles and therefore the direct-current exerts a m.m.f. in 

 quadrature behind the field m.m.f., Fig. 366. The power com- 



FIG. 366. Direction of m.m.fs. in a direct-current generator. 



ponent of the armature current in a synchronous motor exerts 

 a m.m.f. in quadrature ahead of the field m.m.f. and it is there- 

 fore opposed to the m.m.f. of the direct current. 



If Z is the number of conductors on the armature of a bipolar 



generator and is the direct current in each conductor, the arma- 



Z I 



ture m.m.f. is the resultant of -( m.m.fs. of magnitude ^ uni- 



2. & 



