86 SYNCHRONOUS MOTORS 



Lahmeyer made an interesting application of this peculiarity 

 at Bockenheim, where polyphase converters were operated like true 

 synchronous motors. By increasing their excitation, the induced 

 E.M.F. can be raised in such a way as to obtain a secondary voltage 

 of distribution which is constant at all loads. The regulation can 

 be made by hand or automatically. From this point of view rotary 

 converters present a distinct advantage over stationary transformers, 

 which introduce lags and whose secondary voltage necessarily decreases 

 with the load. 



(2) Compensation with Respect to the Generators. It is a two- 

 fold disadvantage, for the generators at the power station, to have 

 the current out of phase, first, because the total current is increased 



S5SO C 



*xr-*w s 



-^c 



1000 2OOO 



Amperes 



X 



FIG. 43- 



and, secondly, because the armature-reaction is greater. To demon- 

 strate this beyond question, let us consider a generator supplying a 

 distribution-system at constant potential U. Let J w and J d be the 

 active and reactive currents supplied to that system, / being the 

 resultant current. Let RI, X\ t Z\, respectively, be the resistance, 

 reactance and impedance of the generator and of the feeders; and 

 let them be considered constant, and as if located in a single apparatus. 



V 



Let tan Ti = -^- be the corresponding reactance-factor. Let us 



^i 

 construct a diagram (Fig. 43) starting from the distribution-voltage 



U, which is to be maintained constant at all loads. 



The necessary E.M.F. 2 will be obtained by compounding, with the 

 voltage OA = U, two vectors representing the volts absorbed by the 

 impedance under the action of the two currents J w and /^. The 



