224 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



which /,' will represent the reactive current transformed into direct 

 current. 



It is also possible to use a rotary converter as a partial generator, 

 by applying mechanical power to its shaft. This mechanical power 

 is added to the electric power applied to the converter from the electrical 

 source (A.C. or D.C.) supplying it. The power-output of the converter, 

 in .such a case, will be equal to the sum of the two power-inputs less the 

 conversion-losses. This case can also be discussed easily by means 

 of the preceding diagram. 



There is still another case, namely, where a rotary converter is used 

 entirely as a generator^ for generating both alternating and direct 

 currents. In such a case the machine is not operating as a rotary 

 converter at all, but as a " double-current " or " omnibus " dynamo. 

 The machine is then a particular kind of alternator and its character- 

 istics should be studied as such. The reactions due to the two kinds 

 of current no longer compensate, but add, themselves; hence" there 

 will be sparking at the brushes unless their position be shifted with 

 the load; and the heating effects will be increased instead of decreased, 

 as compared with the operation of the same machine as a rotary 

 converter. 



Phase-Converters. Instead of making a rotary converter produce 

 direct current when supplied with three-phase current, it could be 

 made to supply two-phase alternating current. The reactions occurring 

 in such a machine would be very interesting, because they would be 

 much more complicated than in the case of ordinary rotary converters. 

 In fact, the (two-phase) currents generated by the machine would 

 no longer have a definite, fixed, phase-relation with the E.M.F., as in 

 the case of the direct current, but they would have a lag which would 

 vary with the reactance in the external circuit. 



It could again be seen easily, by the same reasoning as before, that 

 since the power applied to the machine, and the power delivered by 

 it have nearly the same values, the transverse reactions due to the 

 active current must practically offset or balance each other, leaving 

 only the direct reactions due to the reactive currents. The latter can 

 be evaluated separately and we can thus obtain, for each value of the 

 power output and of the lag in the secondary circuit, the resultant 

 magnetomotive force produced by the reaction of the armature on the 

 magnetic circuit. 



