216 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



which is tangent to this circle, is farther away from the axis Ox; hence 

 ON is increased. 



Second, if the coefficient of self-induction of the transformers is 

 decreased, while the other quantities remain unchanged, the magnetiz- 

 ing current corresponding to zero-load will increase; hence ON is 

 increased. 



Third, if the magnetic leakage is decreased, then increases, and, 



<7 



consequently, the diameter of the circle also increases, causing as before 

 the point M to move farther away from Ox, and increasing ON. 



To sum up, then, the limiting load on a rotary converter can be 

 increased: i, by diminishing the frequency of the A.C. source', 2, 

 by reducing the self-induction of the transformers; 3, by reducing the 

 magnetic leakage. 



These facts have been all verified experimentally. 



II. Let us now consider the rotary converter as a transformer of 

 alternating into direct current. 



The rotary converter used in the previous experiments was operated 

 regularly at full load with the transformer connected to a suitable 

 source of alternating current supply. 



In order to regulate the voltage of the direct current produced by 

 the converter, an (A.C) induction-regulator having a high coefficient 

 of magnetic leakage was included in the primary circuit of the trans- 

 former. The rotary converter then became subject to speed oscilla- 

 tions of long period as soon as its load was increased to half the load 

 which was carried without the induction- regulator. To explain this 

 fact we shall show that every speed-increment of the rotary converter 

 causes an increase in the difference of potential at its terminals. 



Let us refer again to the converter-diagram. Let OA (Fig. 28), 

 represent the difference of A.C. potential at the terminals of the con- 

 verter; OC, the supply-voltage which, in this case, is constant; 0, 

 the phase-angle between these two E.M.F.'s; AD, the active current, 

 including the current corresponding to friction, eddy currents, etc., 

 DC, the reactive current, counted as positive on the right side of 

 the axis of currents BY, and counted as negative on the left side 

 thereof. 



Every increment of speed of the converter causes a decrease of the 

 angle 0. Consequently the diagram shows that, OC being con- 

 stant, the active current AD will decrease (to AD') and the reac- 

 tive current (DC) will increase (to D'C')- Moreover, as in the 



