200 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



it is magnetizing and negative if counted to the left. The upper sign 

 applies in the first case, and the lower sign in the second case. Under 

 those conditions the diagram can now be used for determining the 

 locus of the points C and the variations of E, when the power is con- 

 stant, if the generator E.M.F. be maintained constant as in the case 

 of synchronous motors. We have in this case, simply, 



P= tlw, 



so that, for each value of I w , and, consequently, for each position of the 

 right line DQ, the value of s, and, therefore, the position of the point 

 O, are known; and, from these points, circles of radius E can be drawn, 



whose respective intersections with the right lines DQ give the C 

 points required. It is possible, thus, to draw the " V " curves analogous 

 to those of synchronous motors, and the curves of the corresponding 

 , values of e. But these load-conditions for constant power no longer 

 present in the case of rotary converters the same practical interest 

 as in the case of synchronous motors, because the variation of e would 

 be very troublesome. 



Different Values of the Excitation, with Constant Power and 

 Constant Potential. V-Curves for Constant Potential. The pre- 

 ceding diagram (Figs. 16 and 17) also gives the immediate solution 

 of the more practical problem l which consists in determining the 

 current-values, /, corresponding to different excitations, with constant 



1 The case considered is, as yet, more of theoretical than of practical interest, 

 because it assumes that the E.M.F. is maintained absolutely constant, a condition 

 which, as will be seen later, can be realized only approximately. In the general 

 case therefore both e and E will vary. 



