CHAPTER IV 

 OPERATION OF SEVERAL ROTARY CONVERTERS IN PARALLEL 



THE parallel working of rotary converters is a much more difficult 

 matter than the parallel working of ordinary generators, owing to the 

 fact that the load has a tendency to distribute itself unequally, without 

 any correcting action in the case of rotary converters. 



Any increase of speed occurring in a converter causes the alternating 

 current to lead in phase with respect to the induced E.M.F. This 

 strengthens the magnetic field of the converter, and, consequently, 

 causes the induced E.M.F. to be still further increased. Therefore, 

 there is a tendency to unstable operation. To avoid the unequal 

 distributions of load in rotary converters which are connected in parallel, 

 they not only require careful attendance, but their design and con- 

 struction demand much care, because the various converters intended 

 for parallel working should, as nearly as possible, have the same 

 armature-resistance and the same magnetic reluctance in the magnetic 

 circuits of the field-magnets; in fact, the magnetic leakage and the 

 magnetization curve should be substantially the same for all the 

 machines. 



It is often necessary to give up the attempt to compound the rotary 

 converters and to use only shunt-wound rotary converters, for parallel 

 working. In any case when compound windings are used it is almost 

 always necessary to adjust these windings after the machines are in 

 position, hi order to make them run in balance at all loads. It is 

 understood, of course, that an " equalizer " connection is necessary 

 between the different machines as in the case of all other direct-current 

 compound-wound dynamos connected in parallel. 



It is more difficult still to make the converters run in balance when, 

 instead of being coupled directly, they are coupled through feeders 

 supplying current to a line which is common to all of them, as, for 

 instance, a section of trolley or of third-rail conductor, in electric 

 railway operation. In such cases it has been found necessary to 



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