212 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



the armature; and also of increasing the lag of the current in the 

 supply-circuit, thereby reducing the output-capacity of the generator, 

 increasing the voltage drop in the line, etc. In a word, this method 

 has all the faults and objections due to heavy reactive currents, in addi- 

 tion to which the commutation of the machine is much less satisfactory, 

 there being more tendency to sparking, owing to the shortened air-gap. 



This method, which was used by certain concerns, has now been 

 abandoned altogether. It is referred to here merely to show the ease 

 with which it is possible to calculate the excitation for the conditions, 

 obtaining in this case as well as in the preceding cases. This method 

 has one advantage, however, that of making the satisfactory performance 

 of the converter more independent of the form of the E.M.F. curve of 

 the generator. 



Conclusion. It has been shown, in what precedes, that the vector- 

 diagram for synchronous motors, when referred to two axes, lends itself, 

 as the result of natural simple extensions, to the study of the rotary 

 converter and enables its conditions of operation to be analyzed for 

 the most varied cases. This method of analysis serves to render more 

 intelligible the very complex problem involved in the voltage regula- 

 tion of the rotary converter, which is, perhaps, the most complicated 

 problem presented in connection with alternating-current machinery. 



The methods set forth in the preceding pages not only enable the 

 phenomena to be foreseen qualitatively, but it also enables them to be 

 calculated numerically, by combining the diagrams, or the equations 

 which are derived from them, with the data obtained from experiments 

 or tests. 



